Method and apparatus for determining maximum gain of Raman fiber amplifier
11251871 · 2022-02-15
Assignee
Inventors
- Chengpeng Fu (Hubei, CN)
- Jintao Tao (Hubei, CN)
- Menghui Le (Hubei, CN)
- Cuihong Zhang (Hubei, CN)
- Di Fang (Hubei, CN)
- Qinlian Bu (Hubei, CN)
- Chunpin Yu (Hubei, CN)
- Fei LIU (Hubei, CN)
- Peng Zhang (Hubei, CN)
Cpc classification
H01S2301/02
ELECTRICITY
International classification
H01S3/13
ELECTRICITY
H04B10/291
ELECTRICITY
H04B10/071
ELECTRICITY
Abstract
The present disclosure relates to a technical field of optical communication, and provides a method and an apparatus for determining maximum gain of Raman fiber amplifier. Wherein the method includes obtaining transmission performance parameters of a current optical fiber transmission line; respectively obtaining impact factors A.sub.1, A.sub.2, A.sub.4 according to a distance between a joint and a pump source, a fiber loss coefficient, and a fiber length included in the transmission performance parameters; calculating a joint loss value Att.sub.Aeff according to a distance between a joint and a pump source, a fiber loss coefficient, and looking up impact factor A.sub.3 according to Att.sub.Aeff; determining an actual maximum gain which may actually be achieved by the Raman fiber amplifier according to A.sub.1, A.sub.2, A.sub.3, A.sub.4. The actual maximum gain obtained in the present disclosure is the maximum gain that may be achieved over all input power ranges, and the original signal in system is kept to operate at a fixed gain, such that a gain locking effect is realized, and fluctuation of existing transmission signal power caused by signal change in transmission fiber link is avoided.
Claims
1. A method for determining a maximum gain of a Raman fiber amplifier, characterized in that a relationship between the maximum Raman gain and a 0 km joint loss Att.sub.point[i] equivalent to a joint loss at different positions of one or more types of fibers, a relationship between the maximum Raman gain and a 0 km joint loss Att.sub.coefficient[j] equivalent to a joint loss caused by a loss coefficient of the fibers, a relationship between the maximum Raman gain and a 0 km joint loss AttAeffuq equivalent to a joint loss caused by a mode field diameter of the fibers, and a relationship between the maximum Raman gain and a fiber length are pre-configured, where i is a distance from a joint to a pump source, j is the loss coefficient of the fibers, and k is the mode field diameter of the fibers, the method comprises: obtaining, by an optical time domain reflectometer (OTDR) including a control unit, a modulated signal from the control unit, an optical circulator and a photodetector, transmission performance parameters of a current optical fiber transmission line, the transmission performance parameters including a distance between the joint and the pump source, a fiber loss coefficient, and a fiber length; looking up the relationship between the maximum Raman gain and the joint loss Att.sub.point[i], the relationship between the maximum Raman gain and the joint loss Att.sub.coefficient[j], and the relationship between the maximum Raman gain and the fiber length according to the distance between the joint and the pump source, the fiber loss coefficient, and the fiber length included in the transmission performance parameters to obtain a maximum gain impact factor A.sub.1, a maximum gain impact factor A.sub.2, and a maximum gain impact factor A.sub.4, respectively; calculating a 0 km joint loss Att.sub.Aeff equivalent to a joint loss caused by the mode field diameter of the fiber in the current fiber transmission line according to the distance between the joint and the pump source and the fiber loss coefficient, and looking up the relationship between the maximum Raman gain and the joint loss Att.sub.point[k] according to the joint loss Att.sub.Aeff to obtain a maximum gain impact factor A.sub.3; determining the maximum gain G.sub.max_factual which the Raman fiber amplifier can actually achieve according to the impact factors A.sub.1, A.sub.2, A.sub.3, and A.sub.4.
2. The method for determining a maximum gain of a Raman fiber amplifier of claim 1, characterized in that calculating a 0 km joint loss Att.sub.Aeff equivalent to a joint loss caused by the mode field diameter of the fiber in the current fiber transmission line according to the distance between the joint and the pump source and the fiber loss coefficient, and looking up the relationship between the maximum Raman gain and the joint loss Att.sub.point[k] according to the joint loss Att.sub.Aeff to obtain a maximum gain impact factor A.sub.3, further comprises: obtaining a 0 km-equivalent joint loss Att.sub.point according to the distance between the joint and the pump source, and obtaining a 0 km-equivalent joint loss Att.sub.coefficient according to the fiber loss coefficient; obtaining a total joint loss Pointloss of the transmission line by using out-of-band ASE, the total joint loss Pointloss being also recorded as Att.sub.Toal; calculating a 0 km-equivalent joint loss Att.sub.Aeff caused by the mode field diameter in the current fiber transmission line according to Att.sub.Aeff=Att.sub.Toal−Att.sub.point−Att.sub.coefficient; and looking up the relationship between the maximum Raman gain and the joint loss Att.sub.Aeff[k] according to the joint loss Att.sub.Aeff to obtain the maximum gain impact factor A.sub.3.
3. The method for determining a maximum gain of a Raman fiber amplifier of claim 2, characterized in that obtaining a total joint loss Pointloss of the transmission line by using out-of-band ASE, further comprises: obtaining an out-of-band ASE power ASE.sub.out-of-band, and calculating the total joint loss Pointloss according to a formula Att.sub.total=(ASE.sub.out-of-band−k*P.sub.pump−b)/(k+1), where ASE.sub.out-of-band is detected out-of-band ASE power, P.sub.pump is pump power for calculating the joint loss, Att.sub.Toal is the total joint loss, k is a tilt of the linear relationship, and b is an intercept of the straight line.
4. The method for determining a maximum gain of a Raman fiber amplifier of claim 1, characterized in that the relationship between the maximum Raman gain and the joint loss Att.sub.point[i], the relationship between the maximum Raman gain and the joint loss Att.sub.coefficient[j], and the relationship between the maximum Raman gain and the joint loss Att.sub.Aeff[l] further comprises: calculating an actual maximum gain value according to each loss value Att.sub.point[i], and dividing the actual maximum gain value by a calibrated maximum gain value to obtain a corresponding impact factor; establishing a relationship between each loss value Att.sub.point[i] and the corresponding impact factor; calculating an actual maximum gain value according to each loss value Att.sub.coefficient[j], and dividing the actual maximum gain value by the calibrated maximum gain value to obtain a corresponding impact factor; establishing a relationship between each loss value Att.sub.coefficient[j] and the corresponding impact factor; and calculating an actual maximum gain value according to each loss value Att.sub.Aeff[l], and dividing the actual maximum gain value by the calibrated maximum gain value to obtain a corresponding impact factor; establishing a relationship between each loss value Att.sub.Aeff[l] and the corresponding impact factor.
5. The method for determining a maximum gain of a Raman fiber amplifier of claim 1, characterized in that determining the maximum gain G.sub.max_factual which the Raman fiber amplifier can actually achieve according to the impact factors A.sub.1, A.sub.2, A.sub.3, and A.sub.4, further comprises: calculating an equivalent impact factor A by a formula A=A.sub.1*A.sub.2*A.sub.3*A.sub.4 according to the impact factors A.sub.1, A.sub.2, A.sub.3 and A.sub.4; calculating the actual maximum gain value G.sub.max_factual by a formula G.sub.max_factual=G.sub.max_calibration*A, where G.sub.max_calibration is a calibrated maximum gain of the Raman fiber amplifier.
6. The method for obtaining a method for controlling automatic gain of Raman fiber amplifier of claim 5, characterized in that when the Raman fiber amplifier is a distributed Raman fiber amplifier, the calibrated maximum gain G.sub.max_calibration is obtained by the following steps: establishing a relational expression between a gain tilt and the maximum gain through collecting maximum gain values of the Raman fiber amplifier under various gain tilts in advance; looking up the relational expression between a gain tilt and the maximum gain according to the gain tilt of the current fiber transmission line to obtain the calibrated maximum gain G.sub.max_calibration.
7. The method for controlling automatic gain of Raman fiber of claim 6, characterized in that establishing a relational expression between a gain tilt and the maximum gain comprises: when Tilt<Tilt.sub.turning point,
G.sub.max_calibration=k.sub.01*Tilt+b.sub.01; when Tilt≥Tilt.sub.turning point,
G.sub.max_calibration=k.sub.02*Tilt+b.sub.02; looking up the relational expression between a gain tilt and the maximum gain according to the gain tilt of the current fiber transmission line to obtain the calibrated maximum gain G.sub.max_calibration, further comprises; calculating the calibrated maximum gain G.sub.max_calibration by substituting a Tilt setting value into a corresponding formula of the above two formulas.
8. The method for determining a maximum gain of a Raman fiber amplifier of claim 1, characterized in that the 0 km joint loss Att.sub.point[i] equivalent to a joint loss at different positions of one or more types of fibers, further comprises: the value Att.sub.point is obtained by establishing in a control unit a table of 0 km-equivalent joint loss varying with a position in the fiber and then obtaining a 0 km-equivalent joint loss value for a position in the fiber by looking up the table and interpolation.
9. The method for determining a maximum gain of a Raman fiber amplifier of claim 1, characterized in that the 0 km joint loss Att.sub.coefficient[j] equivalent to a joint loss caused by a loss coefficient of the fibers, further comprises: the value Att.sub.coefficient is obtained by establishing in a control unit a table of 0 km-equivalent joint loss varying with a calibrated loss coefficient of the fibers and then obtaining a 0 km-equivalent joint loss value for a fiber loss coefficient by looking up the table and interpolation.
10. An apparatus for determining a maximum gain of a Raman fiber amplifier, characterized in comprising: at least one processor; and a memory in communication with the at least one processor, the memory having instructions stored therein, and the instructions, when executed by the at least one processor, causing the at least one processor to perform following steps: obtaining, by an OTDR including a control unit, a modulated signal from the control unit, an optical circulator and a photodetector, transmission performance parameters of a current optical fiber transmission line, the transmission performance parameters including a distance between the joint and the pump source, a fiber loss coefficient, and a fiber length; looking up the relationship between the maximum Raman gain and the joint loss Att.sub.point[i], the relationship between the maximum Raman gain and the joint loss Att.sub.coefficient[j], and the relationship between the maximum Raman gain and the fiber length according to the distance between the joint and the pump source, the fiber loss coefficient, and the fiber length included in the transmission performance parameters to obtain a maximum gain impact factor A.sub.1, a maximum gain impact factor A.sub.2, and a maximum gain impact factor A.sub.4, respectively; calculating a 0 km joint loss Att.sub.Aeff equivalent to a joint loss caused by the mode field diameter of the fiber in the current fiber transmission line according to the distance between the joint and the pump source and the fiber loss coefficient, and looking up the relationship between the maximum Raman gain and the joint loss Att.sub.pomt[k] according to the joint loss Att.sub.Aeff to obtain a maximum gain impact factor A.sub.3; and determining the maximum gain G.sub.max_factual which the Raman fiber amplifier can actually achieve according to the impact factors A.sub.1, A.sub.2, A.sub.3, and A.sub.4, wherein a relationship between the maximum Raman gain and a 0 km joint loss Att.sub.point[i] equivalent to a joint loss at different positions of one or more types of fibers, a relationship between the maximum Raman gain and a 0 km joint loss Att.sub.coefficient[j] equivalent to a joint loss caused by a loss coefficient of the fibers, a relationship between the maximum Raman gain and a 0 km joint loss Att.sub.Aeff[k] equivalent to a joint loss caused by a mode field diameter of the fibers, and a relationship between the maximum Raman gain and a fiber length are pre-determined, where i is a distance from a joint to a pump source, j is the loss coefficient of the fibers, and k is the mode field diameter of the fibers.
11. The apparatus of claim 10, characterized in that calculating a 0 km joint loss Att.sub.Aeff equivalent to a joint loss caused by the mode field diameter of the fiber in the current fiber transmission line according to the distance between the joint and the pump source and the fiber loss coefficient, and looking up the relationship between the maximum Raman gain and the joint loss Att.sub.point[k] according to the joint loss Att.sub.Aeff to obtain a maximum gain impact factor A.sub.3, further comprises: obtaining a 0 km-equivalent joint loss Att.sub.point according to the distance between the joint and the pump source, and obtaining a 0 km-equivalent joint loss Att.sub.coefficient according to the fiber loss coefficient; obtaining a total joint loss Pointloss of the transmission line by using out-of-band ASE, the total joint loss Pointloss being also recorded as Att.sub.Toal; calculating a 0 km-equivalent joint loss Att.sub.Aeff caused by the mode field diameter in the current fiber transmission line according to Att.sub.Aeff=Att.sub.Toal−Att.sub.point−Att.sub.coefficient; and looking up the relationship between the maximum Raman gain and the joint loss Att.sub.Aeff[k] according to the joint loss Att.sub.Aeff to obtain the maximum gain impact factor A.sub.3.
12. The apparatus of claim 11, characterized in that obtaining a total joint loss Pointloss of the transmission line by using out-of-band ASE, further comprises: obtaining out-of-band ASE power ASE.sub.out-of-band, and calculating the total joint loss Pointloss according to a formula Att.sub.total=(ASE.sub.out-of-band−k*P.sub.pump−b)/(k+1), where ASE.sub.out-of-band is detected out-of-band ASE power, P.sub.pump is pump power for calculating the joint loss, Att.sub.Toal is the total joint loss, k is a tilt of the linear relationship, and b is an intercept of the straight line.
13. The apparatus of claim 10, characterized in that the relationship between the maximum Raman gain and the joint loss Att.sub.point[i], the relationship between the maximum Raman gain and the joint loss Att.sub.coefficient[j], and the relationship between the maximum Raman gain and the joint loss Att.sub.Aeff[l], further comprises: calculating an actual maximum gain value according to each loss value Att.sub.point[i], and dividing the actual maximum gain value by a calibrated maximum gain value to obtain a corresponding impact factor; establishing a relationship between each loss value Att.sub.point[i] and the corresponding impact factor; calculating an actual maximum gain value according to each loss value Att.sub.coefficient[j], and dividing the actual maximum gain value by the calibrated maximum gain value to obtain a corresponding impact factor; establishing a relationship between each loss value Att.sub.coefficient[j] and the corresponding impact factor; and calculating an actual maximum gain value according to each loss value Att.sub.Aeff[l], and dividing the actual maximum gain value by the calibrated maximum gain value to obtain a corresponding impact factor; establishing a relationship between each loss value Att.sub.Aeff[l] and the corresponding impact factor.
14. The apparatus of claim 10, characterized in that determining the maximum gain G.sub.max_factual which the Raman fiber amplifier can actually achieve according to the impact factors A.sub.1, A.sub.2, A.sub.3, and A.sub.4, further comprises: calculating an equivalent impact factor A by a formula A=A1*A2*A3*A4 according to the impact factors A.sub.1, A.sub.2, A.sub.3 and A.sub.4; calculating the actual maximum gain value G.sub.max_factual according to a formula G.sub.max_factual=G.sub.max_calibration*A, where G.sub.max_calibration calibration is a calibrated maximum gain of the Raman fiber amplifier.
15. The apparatus of claim 14, characterized in that when the Raman fiber amplifier is a distributed Raman fiber amplifier, the calibrated maximum gain G.sub.max_calibration is obtained by the following steps: establishing a relational expression between a gain tilt and the maximum gain through collecting maximum gain values of the Raman fiber amplifier under various gain tilts in advance; looking up the relational expression between a gain tilt and the maximum gain according to the gain tilt of the current fiber transmisstion line to obtain the calibrated maximum gain G.sub.max_calibration.
16. The apparatus of claim 15, characterized in that establishing a relational expression between a gain tilt and the maximum gain comprises: when Tilt<Tilt.sub.turning point,
G.sub.max_calibration=k.sub.01*Tilt+b.sub.01; when Tilt≥Tilt.sub.turning point,
G.sub.max_calibration=k.sub.02*Tilt+b.sub.02; and looking up the relational expression between a gain tilt and the maximum gain according to the gain tilt of the current fiber transmission line to obtain the calibrated maximum gain G.sub.max_calibration, further comprises: calculating the calibrated maximum gain G.sub.max_calibration by substituting a Tilt setting value into one corresponding formula of the above two formulas.
17. The apparatus of claim 10, characterized in that the 0 km joint loss Att.sub.point[i] equivalent to a joint loss at different positions of one or more types of fibers, further comprises: the value Att.sub.point is obtained by establishing in a control unit a table of 0 km-equivalent joint loss varying with a position in the fibers and then obtaining a 0 km-equivalent joint loss value for a position in the fiber by looking up the table and interpolation.
18. The apparatus of claim 10, characterized in that the 0 km joint loss Att.sub.coefficient[j] equivalent to a joint loss caused by a loss coefficient of the fibers, further comprises: the value Att.sub.coefficient is obtained by establishing in a control unit a table of 0 km-equivalent joint loss varying with a calibrated loss coefficient of the fibers and then obtaining a 0 km-equivalent joint loss value for a fiber loss coefficient by looking up the table and interpolation.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In order to more clearly illustrate embodiments of the present disclosure or technical solutions in the prior art, the drawings used in the embodiments or the prior art description will be briefly described below. Obviously, the drawings in the following description are only some embodiments of the present disclosure, for those ordinary skill in the art, other drawings may be obtained according to these drawings without paying any inventive labor.
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REFERENCE SIGNS
(23) TABLE-US-00001 1: Pump laser group 1; 2: Pump laser group 2; 3: Control unit; 4: Modulated signal of OTDR; 5: Circulator; 6: OTDR detector; 7: Pump combination WDM; 8: Pump/signal combination WDM; 9: Out-of-band/in-band split DM; 10: Coupler; 11: Out-of-band ASE detector; 12; In-band photodetector; 13: OTDR wavelength and signal wavelength combination WDM; 14: Additional laser for OTDR.
DETAILED DESCRIPTION
(24) In order to make the purpose, the technical solution and advantages of the present disclosure clearer and clearer, the present disclosure will be described in further detail below with reference to the drawings and embodiments. It should be understood that the embodiments described herein are only for the purpose of explaining the present disclosure and are not intended to limit the present disclosure.
(25) In the description of the present disclosure, the orientation or positional relationship indicated by the terms “inner”, “outer”, “longitudinal”, “transverse”, “upper”, “lower”, “top”, “bottom” and the like is based on the orientation or positional relationship shown in the drawings, only for convenience of description of the present disclosure rather than requiring the invention to be constructed and operated in a specific orientation, therefore, it should not be understood as limiting the present disclosure.
(26) In embodiments of the present disclosure, a Raman pump laser is also called as a pump source for short; in each embodiment of the present disclosure, after a first appearance of the specific distance between the joint and the pump source or the specific fiber loss coefficient of the 0 km-equivalent joint loss, the 0 km-equivalent joint loss is used as a short name in corresponding embodiments, and the above description is particularly applicable to embodiment 3 and embodiment 4. In each embodiment of the present disclosure, the 0 km-equivalent joint loss caused by the distance between the joint and the pump source is also described as the 0 km-equivalent joint loss of the fiber node for convenience of description. In the embodiments of the present disclosure, the fiber length generally refers to a transmission distance between a signal transmission and a signal reception, and in a real communication system, it is a distance between two adjacent relay stations, here, the relay may be either an electrical relay or an optical relay.
(27) Further, the technical features involved in each embodiment of the present disclosure described below may be combined with each other as long as they do not conflict with each other.
(28) In
(29) As shown in
(30) The difference between the embodiment shown in
(31) In different application environments, the amplification gain of the Raman fiber amplifier will be doubly limited by pump power itself and impact of environmental factor (including a distance between a joint and a pump source, a loss coefficient of fiber, the mode field diameter of fiber and the length of fiber), therefore, an actual maximum gain G.sub.max_factual of a Raman pump module is defined as the maximum gain that may actually be achieved in its environment (meeting requirements of signal-to-noise ratio and transmission performances, etc.) by this Raman fiber amplifier; a setting gain G.sub.setting of a Raman pump module is defined as a gain value set by a user for a Raman fiber amplifier; a control gain G.sub.operation of a Raman pump module is defined as a gain value actually set for a Raman pump module. Those skilled in the art should understand that the setting gain G.sub.setting of a Raman pump module set by a user may be larger than the actual maximum gain G.sub.max_factual of the Raman fiber amplifier, and may also be less than or equal to the actual maximum gain G.sub.max_factual of the Raman fiber amplifier; if the setting gain G.sub.setting set by the user is larger than the maximum gain G.sub.max_factual, the control gain G.sub.operation of the Raman fiber amplifier is the maximum gain g.sub.max_factual; if the setting gain G.sub.setting set by the user is less than or equal to the maximum gain G.sub.max_factual, the control gain G.sub.operation of the Raman fiber amplifier is the setting gain G.sub.setting. In addition, the corresponding maximum gain will also change in a case of different gain tilts.
(32) It should be emphasized that the expanded description of the subsequent embodiments of the present disclosure may be applied to the distributed Raman fiber amplifier as shown in
(33) The description of each embodiment of the present disclosure may be realized based on the above architectures (e.g., the architectures shown in
(34) When the technical solutions described in the embodiments of the present disclosure are specifically described, the implementation significance of the present disclosure is described by way of example. The main purpose of the present disclosure is to be able to determine the maximum gain, which may be achieved in all input power ranges, in this way, in the aspect of transient control, the original signal of the system may be kept to operate at a fixed gain, i.e. a gain locking effect may be realized. In the prior art, since the actual maximum gain value proposed in the present disclosure may not be determined, therefore, after the power signals P1, P1, and P3 in the initial situation are adjusted and enter the maximum gain control stage in the prior art, if the signals P4˜P50 are suddenly added, at this time, for the P1-P3 signals, because P4˜P50 signal lights sharing the optical power of the pump laser with the signals P1 to P3 are generated, that is to say, when the new P4˜P50 signal lights enter the transmission optical path, the pump laser is unable to generate a higher pump light power, at this time, the result is that the signal transmission optical power of the amplified signals P1-P3 will decrease, which is sometimes fatal for the remote receiving terminals of the P1-P3 signals, and because they have been accustomed to the power intensity of P1-P3 in history, and the sudden intervention of the P4˜P50 signals will result in the decrease of P1-P3 transmission optical power, even leads to a signal loss or a signal decoding error at the receiving terminal etc. The significance of the present disclosure is to solve the above problems in the prior art.
Embodiment 1
(35) An embodiment of the present disclosure provides a method for determining a maximum gain (specifically refers to the actual maximum gain G.sub.max_factual) of a Raman fiber amplifier. Since the embodiment of the present disclosure may be applied to the apparatus architectures corresponding to
(36) In step 201, obtaining transmission performance parameters of a current optical fiber transmission line, where the transmission performance parameters include a distance between a joint and a pump source, a fiber loss coefficient, and a fiber length.
(37) The obtaining mode may be detecting joint losses, fiber loss coefficients and fiber lengths at different positions of the fiber in the OTDR mode under the control of the above control unit 3. For example, the control unit 3 may specifically adopt architectures with OTDR detection function shown in
(38) In step 202, looking up the relationship between the maximum Raman gain and the joint loss Att.sub.point[i] to obtain a maximum gain impact factor A.sub.1 according to the distance between the joint and the pump source included in the transmission performance parameters.
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(40) In step 203, looking up the relationship between the joint loss value Att.sub.coefficient[j] and the maximum Raman gain to obtain a maximum gain impact factor A.sub.2 according to the fiber loss coefficient included in the transmission performance parameters.
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(42) In step 204, looking up the relationship between the maximum Raman gain and the fiber length of transmission line to obtain a maximum gain impact factor A.sub.4 according to the fiber length included in the transmission performance parameters.
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(44) In step 205, calculating a 0 km joint loss Att.sub.Aeff equivalent to a joint loss caused by the mode field diameter in the current fiber transmission line according to the fiber loss coefficient, the distance between the joint and the pump source, and looking up the relationship between the joint loss Att.sub.point[k] and the maximum Raman gain to obtain a maximum gain impact factor A.sub.3 according to the joint loss value Att.sub.Aeff.
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(46) In step 206, determining the actual maximum gain G.sub.max_factual which may actually be achieved by the Raman fiber amplifier according to the impact factors A.sub.1, A.sub.2, A.sub.3, and A.sub.4.
(47) According to the embodiment of the present disclosure, after obtaining the distance between the joint and the pump source, and the fiber loss coefficient both affecting the actual gains of an optical Raman fiber amplifier, its loss relationship is corelated with the out-of-band ASE joint loss by a mode of equalizing a fiber loss coefficient and a distance between the joint and the pump source to be a joint loss at 0 km (since the existing out-of-band ASE detection is performed on the pump laser side, i.e. at the 0 km, therefore, it is necessary to convert the associated impact into a 0 km joint loss so as to be able to be calculated together), and the process of calculating the mode field diameter joint loss Att.sub.Aeff is realized according to the 0 km-equivalent joint loss of the distance between the joint and the pump source and the 0 km-equivalent joint loss of the fiber loss coefficient, thus the fiber mode field diameter among factors affecting the actual gains of a Raman fiber amplifier is obtained, thus possibility for solving the actual maximum gains is provided, i.e. obtaining the actual maximum gains by comprehensively considering four impacting factors of the distance between the joint and the pump source, the fiber loss coefficient, the mode field diameter of the fibers and the fiber length. The actual maximum gain is the maximum gain that may be achieved in all input power ranges, in this way, in the aspect of transient control, the original signal of the system may be kept to operate at a fixed gain, i.e. a gain locking effect may be realized, and a fluctuation of existing transmission signal power caused by signal changes in transmission fiber link is avoided.
(48) Wherein when solving the impact factors, the embodiments of the present disclosure may also obtain the impact factor for solving the maximum gain by pre-storing respective relationship parameters, and by interpolation, and temporarily by formula calculation and other methods, which enables the method proposed by the embodiments of the present disclosure may be realized by an existing architecture carrying a control unit.
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(50) Combined with the embodiment of the present disclosure, for calculating the joint loss Att.sub.Aeff according to the fiber loss coefficient, the distance between the joint and the pump source, and looking up the relationship between the joint loss Att.sub.point[k] and the maximum Raman gain to obtain a maximum gain impact factor A.sub.3 according to the joint loss Att.sub.Aeff involved in step 205, the embodiment of the present disclosure further provides a specific implementation mode, as shown in
(51) In step 2051, obtaining the 0 km-equivalent joint loss Att.sub.point[i] according to the distance between the joint and the pump source; obtaining the 0 km-equivalent joint loss Att.sub.coefficient[j] according to the fiber loss coefficient.
(52) Here, the relationship between the distance between the joint and the pump source and the 0 km-equivalent joint loss Att.sub.point[i], similarly to the relationship between the 0 km-equivalent joint loss value Att.sub.point[i] and the maximum Raman gain involved in Embodiment 1 of the present disclosure, may be obtained by calculating corresponding formula (the subsequent content will be specifically described in Embodiment 3), it may also be obtained by looking up a pre-configured calculated table and/or a curve fitted on the basis of the corresponding formula.
(53) In step 2052, obtaining a total joint loss Pointloss of the transmission line by using the out-of-band ASE, where the total joint loss Pointloss is also recorded as Att.sub.Toal.
(54) An embodiment of the present disclosure provides a preferred implementation, i.e. selecting a specified pump laser pump1, calculating out-of-band ASE detection values corresponding to each output power of pump1 in a case where the total joint loss Pointloss is 0, and solving parameters k and b in the formula 0=ASE.sub.out-of-band−k*P.sub.pump−b according to the out-of-band ASE detection values corresponding to each output power; then the total joint loss Pointloss is presented as Pointloss=(ASE.sub.out-of-band−k*P.sub.pump−b)/(k+1).
(55) The reason why to select a specified pump laser pump1 here is that the participation of a plurality of pump lasers in the solution of parameters k and b at the same time, may lead to instability of test process, thus, lead to the accuracy of the calculated parameters k and b not high. However, the total joint loss Pointloss does not vary with the number of pump lasers, therefore, specifying a pump laser pump1 to calculate the above total joint loss Pointloss may simplify the calculation process and improve the accuracy of the calculation. Of course, it is also within the protection scope of the embodiment of the present disclosure to use a plurality of pump lasers simultaneously to calculate the total joint loss based on the idea proposed by the embodiment of the present disclosure.
(56) In step 2053, calculating a 0 km-equivalent joint loss Att.sub.Aeff caused by a mode field diameter in a current fiber transmission line based on Att.sub.Aeff=Att.sub.Toal−Att.sub.point−Att.sub.coefficient.
(57) In an embodiment of the present disclosure, the Att.sub.point and Att.sub.coefficient may be obtained by looking up a table as described in the following contents. Establishment of the table is specifically described in subsequent Embodiment 3 and Embodiment 4 of the present disclosure (wherein for different types (referring specifically to different fiber attenuation coefficients) of fibers used in different positions and different regions, the fiber attenuation coefficient may individually calculated in sections, and the calculation of each segment may be completed by specifically referring to Embodiment 4, and its final presentation as the impact factor A.sub.2 may be completed by referring to the above example of A.sub.1=A.sub.1-1*A.sub.1-2* . . . *A.sub.1-u, which will not be described in detail here).
(58) In step 2054, looking up the relationship between the joint loss value Att.sub.Aeff[k] and the maximum Raman gain to obtain a maximum gain impact factor A.sub.3 according to the joint loss value Att.sub.Aeff.
(59) Through the above steps 2051-2054, a conversion mechanism among Att.sub.Toal, Att.sub.point, Att.sub.coefficient and Att.sub.Aeff is provided, thus Att.sub.Aeff which is difficult to obtain, may be obtained according to Att.sub.Toal, Att.sub.point, Att.sub.coefficient which are easy to calculate, so as to solve transmission performance parameters which affect the actual amplification gain.
(60) Referring to
(61) obtaining an actual maximum gain according to each loss value Att.sub.point[i] (in Embodiment 3, how to implement is described in detail), and dividing the actual maximum gain by a calibrated maximum gain to obtain a corresponding impact factor; and establishing a corresponding relationship between each loss value Att.sub.point[i] and the corresponding impact factor;
(62) obtaining an actual maximum gain according to each loss value Att.sub.coefficient[j] (in Embodiment 4, how to implement is described in detail), and dividing the actual maximum gain by the calibrated maximum gain value to obtain a corresponding impact factor; and establishing a corresponding relationship between each loss value Att.sub.coefficient[j] and the corresponding impact factor;
(63) obtaining an actual maximum gain according to each loss value Att.sub.Aeff[l] (derived from Embodiment 3, Embodiment 4, and Embodiment 5 combined with the formula Att.sub.Aeff=Att.sub.Toal−Att.sub.point−Att.sub.coefficient in step 2053), dividing the actual maximum gain by the calibrated maximum gain to obtain a corresponding impact factor; and establishing a corresponding relationship between each loss value Att.sub.Aeff[l] and the corresponding impact factor.
(64)
(65) In the embodiment of the present disclosure, for determining the actual maximum gain G.sub.max_factual which may actually be achieved by the Raman fiber amplifier according to the impact factors A.sub.1, A.sub.2, A.sub.3 and A.sub.4, involved in step 206, its implementation process is described below through a specific formula derivation:
(66) calculating an equivalent impact factor A by a formula A=A.sub.1*A.sub.2*A.sub.3*A.sub.4 according to the impact factors A.sub.1, A.sub.2, A.sub.3 and A.sub.4; calculating the actual maximum gain G.sub.max_factual according to a formula G.sub.max_factual=G.sub.max_calibration*A; where G.sub.max_calibration is a calibrated maximum gain of a Raman fiber amplifier, or it may also be described as the ideal maximum gain in the current state after the Raman fiber amplifier leaves the factory without considering each above-mentioned impact factor.
(67) Combined with the embodiment of the present disclosure, if the Raman fiber amplifier is implemented by a single pump laser, the corresponding calibrated maximum gain may be calculated according to the factory-set maximum power of the pump laser, or be directly obtained according to the calibrated maximum gain which is set when the pump laser leaves the factory. However, in the specific implementation process, the distributed Raman pump lasers are mostly used under a general application environment, therefore, the embodiment of the present disclosure further provides a method for determining the calibrated maximum gain G.sub.max_calibration in the distributed Raman fiber amplifier, comprising:
(68) establishing a relational expression between a gain tilt and the maximum gain through collecting maximum gain values of the Raman fiber amplifier under various gain tilts in advance;
(69) and looking up the above established relational expression between the gain tilt and the maximum gain and obtaining the calibrated maximum gain G.sub.max_calibration through the gain tilt of the current fiber transmission line. Taking
(70) The presentation mode of relationship between the above gain tilt and the calibrated maximum gain in the embodiment of the present disclosure is usually stored in control unit 3 in the mode of a formula or an array, except for the icon mode shown in
(71) When Tilt<Tilt.sub.turning point,
G.sub.max_calibration=k.sub.01*Tilt+b.sub.01;
(72) When Tilt≥Tilt.sub.turning point,
G.sub.max_calibration=k.sub.02*Tilt+b.sub.02;
(73) Where the k.sub.01, k.sub.02, b.sub.01 and b.sub.02 are correlation coefficients, which may be calculated by calibration or fitting the curve as shown in
(74) Then looking up the above established relational expression between gain tilt and maximum gain and obtaining the calibrated maximum gain G.sub.max_calibration according to the gain tilt of the current fiber transmission line, further comprises:
(75) substituting a Tilt setting value into a corresponding formula of the above two formulas, and obtaining the calibrated maximum gain G.sub.max_calibration.
(76) The embodiment of the present disclosure also provides a implementation method for a 0 km joint loss Att.sub.point[i] equivalent to a joint loss at different positions of one or more types of fibers, including:
(77) the value Att.sub.point is obtained by establishing in a control unit a table of 0 km-equivalent joint loss varying with a position in the fibers (The table of 0 km-equivalent joint loss may be established by the method for solving the Att.sub.point introduced in Embodiment 3), and then obtaining a 0 km-equivalent joint loss value for a position in the fiber by looking up the table and interpolation.
(78) The embodiment of the present disclosure also provides a specific implementation method for 0 km-equivalent joint loss value Att.sub.coefficient[j] equivalent to a joint loss at different positions of one or more types of fibers, including:
(79) the value Att.sub.coefficient is obtained by establishing in a control unit a table of 0 km-equivalent joint loss varying with a calibrated loss coefficient of the fibers (The table of 0 km-equivalent joint loss may be established by the method for solving the Att.sub.coefficient introduced in Embodiment 4), and then obtaining a 0 km-equivalent joint loss value for a fiber loss coefficient by looking up the table and interpolation.
(80) Combined with the embodiment of the present disclosure, after obtaining the actual maximum gain G.sub.max_factual, there also is a preferred extended solution. Specifically, when a gain value is selected as the current operating gain G.sub.operation according to the G.sub.max_factual, and the scenario used by the current method is a distributed Raman pump amplifier, as shown in
(81) In step 207, calculating a gain tilt according to a first relational expression between the out-of-band ASE.sub.out-of-band and the operating gain G.sub.operation, where the first relational expression is ASE.sub.out-of-band+ΔASE=k.sub.1*G.sub.operation+k.sub.2*Tilt+b.sub.1+Att.sub.point.
(82) Wherein k.sub.1 is a tilt factor of the linear relationship between the out-of-band ASE power (dBm) and the gain (dB), K.sub.2 is a tilt factor of the linear relationship between the out-of-band ASE power (dBm) and the gain tilt (dB), and b.sub.1 is an intercept; the k.sub.1, k.sub.2 and b.sub.1 are obtained by calibration, and the correction quantity ΔASE of target ASE, specifically is: when the fiber length is ≥100 km, ΔASE=0; when the fiber length is less than 100 km, ΔASE is determined according to look-up table or interpolation or function fitting. It should be noted that the fiber length of 100 km is only a preferred critical value provided by the embodiment of the present disclosure, in an actual operation process, due to the difference of energy conversion efficiency between a pump light and a signal light caused by difference of fiber materials, its critical length may also be adjusted on the 100 km, and the adjusted technical solution of corresponding fiber length critical value based on the inventive concept of the present disclosure is also within the protection scope of the present disclosure.
(83) In step 208, calculating operating power p.sub.1 of a pump laser group 1 and operating power p.sub.2 of the pump laser group 1, according to the gain tilt calculated based on the first relational expression and the operating gain G.sub.operation, and according to a second relational expression, where the second relational expression is p.sub.1/p.sub.2=k.sub.3*G.sub.operation+k.sub.4*Tilt+b.sub.2.
(84) Where p.sub.1 is output power of the pump laser group 1, p.sub.2 is output power of the pump laser group 2, k.sub.3 is a tilt factor linearly related to the amplifier gain G (whose unit is dB), and k.sub.4 is a tilt factor linearly related to the gain Tilt (whose unit is dB), b.sub.2 is an intercept, and k.sub.3, k.sub.4 and b.sub.2 are all obtained by calibration.
(85) In step 209, adjusting an operating state of the Raman pump laser based on the calculated operating power p.sub.1 of the pump laser group 1 and the calculated operating power p.sub.2 of the pump laser group 1.
(86) Combined with the embodiment of the present disclosure, after obtaining the actual maximum gain G.sub.max_factual, there also is a preferred extended solution, specifically, when a gain value is selected as the current operating gain G.sub.operation according to the G.sub.max_factual, unlike the above method, the scenario using the current method is a single Raman pump amplifier, as shown in
(87) In step 207′, calculating a gain tilt according to a first relational expression between the out-of-band ASE.sub.out-of-band and the operating gain G.sub.operation, wherein the out-of-band ASE.sub.out-of-band is obtained by an actual detection, and the first relational expression is:
ASE.sub.out-of-band+ΔASE=k.sub.1*G.sub.operation+b.sub.1+Att.sub.point;
(88) where k.sub.1 is a tilt factor of the linear relationship between the out-of-band ASE power and the gain, k.sub.2 is a tilt factor of the linear relationship between the out-of-band ASE power and the gain tilt, and b.sub.1 is an intercept; the k.sub.1, k.sub.2 and b.sub.1 are obtained by calibration, ΔASE is a correction quantity of ASE associated with the fiber length;
(89) In step 208′, adjusting the Raman fiber amplifier according to the calculated out-of-band ASE.sub.out-of-band, so that the detected out-of-band ASE power differs from the calculated out-of-band ASE.sub.out-of-band by a preset distance.
Embodiment 2
(90) After a method for determining a maximum gain of a Raman fiber amplifier is proposed in Embodiment 1 of the present disclosure, an embodiment of the present disclosure further provides a method for controlling an automatic gain of a Raman fiber amplifier by using the maximum gain calculated in Embodiment 1, and before performing the method according to the embodiment of the present disclosure, it is necessary to firstly obtain the actual maximum gain G.sub.max_factual that may be achieved by the current amplifier, where the G.sub.max_factual may be obtained by the method described in Embodiment 1. As shown in
(91) In step 301, calculating a signal power P.sub.signal by using a linear relationship among the out-of-band ASE optical power ASE.sub.out-of-band, the in-band ASE optical power ASE.sub.in-band and the gain tilt Tilt.
(92) Wherein the execution environment of step 301 is to adjust the pump laser operation according to the setting gain G.sub.setting set by a user after the Raman fiber amplifier enters the normal operating state, and then detect the out-of-band ASE optical power ASE.sub.out-of-band.
(93) In step 302, obtaining a compensation gain ΔG of the Raman fiber amplifier according to the signal power P.sub.signal and stable signal power P.sub.INU before the Raman pump laser is turned on.
(94) Wherein the gain actually obtained by the amplifier is achieved by the obtained signal power P.sub.signal subtracting the stable signal power P.sub.INU before the Raman pump laser is turned on, G.sub.factual=P.sub.signal−P.sub.INU.
(95) The compensation gain of the Raman fiber amplifier ΔG=G.sub.operation−G.sub.factual.
(96) In step 303, performing gain control of the Raman fiber amplifier according to the compensation gain ΔG, the setting gain G.sub.setting, and the actual maximum gain G.sub.max_factual that the current amplifier may achieve.
(97) The embodiment of the present disclosure provides two reference dimensions of the maximum gain and the actual gain that the current amplifier may achieve for gain control, and provides a reference angle for automatic gain control of the Raman fiber amplifier, and proposes the compensation gain ΔG, therefore, compared with a case in the prior art where a power amplification is only detected through the out-of-band ASE, it may achieve more accurate control. And compared with the equal-step adjustment method commonly adopted in the prior art, since the maximum gain value that may be finally and actually obtained, has already been calculated in the embodiment of the present disclosure, accordingly, the purpose of adjusting gain control of the Raman fiber amplifier according to the setting gain and the actual gain may be quickly achieved.
(98) In the embodiment of the present disclosure, an implementation mode is also provided for performing gain control of the Raman fiber amplifier according to the compensation gain ΔG, the setting gain G.sub.setting, and the actual maximum gain G.sub.max_factual that the current amplifier may achieve involved in step 303, including:
(99) Determining the operating gain G.sub.operation, according to a comparison between the actual maximum gain G.sub.max_factual and the setting gain G.sub.setting, if the setting gain G.sub.setting is less than the actual maximum gain G.sub.max_factual, the operating gain G.sub.operation is set to be the setting gain G.sub.setting+ΔG; if the setting gain G.sub.setting is larger than the actual maximum gain G.sub.max_factual, and ΔG is positive, the operating gain G.sub.operation is set to be the actual maximum gain G.sub.max_factual that may be actually achieved (the reason is that if the calculated ΔG is positive, it is impossible to further increase the parameter value of the actual maximum gain G.sub.max_factual), if the setting gain G.sub.setting is larger than the actual maximum gain G.sub.max_factual, and ΔG is negative, the operating gain G.sub.operation is set to be the actual maximum gain that may be actually achieved G.sub.max_factual−ΔG.
(100) Combined with the embodiment of the present disclosure, for the operating gain G.sub.operation being set to be the setting gain G.sub.setting+ΔG or the maximum gain G.sub.max_factual, a specific method is also provided in the embodiment of the present disclosure, in the distributed Raman pump amplifier, it is implemented as shown in
(101) In step 3031, calculating a gain tilt according to a first relational expression between the out-of-band ASE.sub.out-of-band and the operating gain G.sub.operation, wherein the first relational expression is ASE.sub.out-of-band+ΔASE=k.sub.1*G.sub.operation+k.sub.2*Tilt+b.sub.1+Att.sub.point.
(102) Wherein k.sub.1 is a tilt factor of the linear relationship between the out-of-band ASE power (dBm) and the gain (dB), K.sub.2 is a tilt factor of the linear relationship between the out-of-band ASE power (dBm) and the gain tilt (dB), and b.sub.1 is an intercept; the k.sub.1, k.sub.2 and b.sub.1 are obtained by calibration, and for a correction quantity ΔASE of target ASE, when the fiber length is ≥100 km, ΔASE=0; when the fiber length is <100 km, ΔASE is determined according to a look-up table or interpolation or function fitting.
(103) In step 3032, calculating operating power p.sub.1 of a pump laser group 1 and operating power p.sub.2 of the pump laser group 1 according to the gain tilt calculated based on the first relational expression and the operating gain G.sub.operation, and according to a second relational expression, wherein the second relational expression is p.sub.1/p.sub.2=k.sub.3*G.sub.operation+k.sub.4*Tilt+b.sub.2.
(104) Where p.sub.1 is output power of the pump laser group 1, p.sub.2 is output power of the pump laser group 2, k.sub.3 is a tilt factor linearly related to the amplifier gain G (whose unit is dB), and k.sub.4 is a tilt factor linearly related to the gain tilt Tilt (whose unit is dB), b.sub.2 is an intercept, and k.sub.3, k.sub.4 and b.sub.2 are all obtained by calibration.
(105) In step 3033, adjusting an operating state of a Raman pump laser based on the calculated operating power p.sub.1 of the pump laser group 1 and the calculated operating power p.sub.2 of the pump laser group 1.
(106) Combined with the embodiment of the present disclosure, for the operating gain G.sub.operation being set to be the setting gain G.sub.setting+ΔG or the maximum gain G.sub.max_factual, a specific method is also provided in the embodiment of the present disclosure, in the single Raman pump amplifier, which is implemented as shown in
(107) In step 3031′, calculating a gain tilt according to a first relational expression between an out-of-band ASE.sub.out-of-band and an operating gain G.sub.operation, wherein the out-of-band ASE.sub.out-of-band is obtained by an actual detection, and the first relational expression is:
ASE.sub.out-of-band+ΔASE=k.sub.1*G.sub.operation+b.sub.1+Att.sub.point;
(108) where k.sub.1 is a tilt factor of the linear relationship between the out-of-band ASE power and the gain, k.sub.2 is a tilt factor of the linear relationship between the out-of-band ASE power and the gain tilt, and b.sub.1 is an intercept; the k.sub.1, k.sub.2 and b.sub.1 are obtained by calibration, ΔASE is a correction quantity of ASE associated with the fiber length;
(109) In step 3032′, adjusting the Raman fiber amplifier according to the calculated out-of-band ASE.sub.out-of-band, so that the detected out-of-band ASE power differs from the calculated out-of-band ASE.sub.out-of-band by a preset distance.
(110) Wherein the preset distance may be set according to experience, and is usually set in consideration of the detection accuracy and the size of parameter value.
(111) In embodiment of the present disclosure, for calculating signal power P.sub.signal by using a linear relationship among the out-of-band ASE optical power ASE.sub.out-of-band, the in-band ASE optical power ASE.sub.in-band and the gain tilt Tilt involved in step 301, it is described in detail in the embodiment of the present disclosure, including:
(112) calculating ASE.sub.in-band according to a formula ASE.sub.in-band=k.sub.5*ASE.sub.out-of-band+k.sub.6*Tilt+(k.sub.5−1)*Att.sub.point+b.
(113) Then, calculating signal power P.sub.signal according to a formula P.sub.signal=10*log.sub.10(P.sub.total−10{circumflex over ( )}(ASE.sub.in-band/10)).
(114) where total P.sub.total is total power of the detected in-band optical signal, k.sub.5 is a proportional coefficient of the linear relationship, k.sub.6 is an impact factor on the original in-band and out-band relationship in a case of different gain tilts, and b is an intercept.
(115) According to the embodiment of the disclosure, considering that the gain control accuracy is limited in an actual adjustment process, therefore, in theory, the current gain adjustment may be stopped as long as the difference between the current control operation for adjusting gain and the actually calculated gain result meets a preset gain accuracy requirement, and on the contrary, when ΔG=G.sub.operation−G.sub.factual exceeds the gain accuracy control requirement, G.sub.operation is the calculated target gain G, and ΔG+G.sub.factual is set as a new gain G control quantity to perform iterative calculation, thereby realizing a feedback control; wherein the current actual gain G.sub.factual of the Raman fiber amplifier is obtained by the signal power P.sub.signal subtracting the stable signal power P.sub.INU before the Raman pump laser is turned on, i.e. G.sub.factual=P.sub.signal−P.sub.INU.
(116) In the embodiment of the present disclosure, a preferred implementation mode is provided for obtaining Att.sub.point, specifically, the value Att.sub.point is obtained by establishing in a control unit a table of 0 km-equivalent joint loss varying with a position in the fiber and then obtaining a 0 km-equivalent joint loss value for a position in the fiber by looking up the table and interpolation. The specific operation process may refer to relevant description in Embodiment 1, and will not be described in detail here.
Embodiment 3
(117) The embodiment of the present disclosure also provides a method for determining a 0 km-equivalent joint loss of fiber node in a Raman fiber amplifier, i.e. a 0 km joint loss equivalent according to a distance between a joint and a pump source. The determining method proposed in the embodiment of the present disclosure may be operated by a third-party computer, and the obtained data result may be imported into control unit 3 involved in the embodiments of the present disclosure, and the determining method described in the embodiment of the present disclosure may also be directly performed by the control unit 3, which is not particularly limited here. As described in
(118) In step 401, obtaining a pump transmission power relational expression, a signal transmission power relational expression and an out-of-band ASE power relational expression.
(119) Wherein the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression may be converted into a code program and stored on a third-party computer in advance, for example, the embodiment of the present disclosure provides a feasible mode to organize the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression into a format supported by a numerical solution of ordinary differential equation in Matlab and store in a memory of a third-party computer.
(120) In step 402, dividing a fiber into one or two segments according to a joint loss position set in a fiber line; wherein when the joint loss position is at the starting point of the fiber, the fiber assumes one segment; when the starting point of the fiber is different from the joint loss position by a preset distance, the fiber assumes two segments, and the joint loss position is taken as the demarcation point of two sections of fiber.
(121) The joint loss set at different positions can be generally classified into two types, one of which is that the joint loss is set at the starting point of the fiber, presenting that the above fiber is one section; and the other type of which is that the joint loss is set at a non-starting position of the fiber, at this time, according to the position setting the joint loss, the entire fiber is divided into two segments: the first segment is from the starting point of the fiber to the setting position of the joint loss, and the second segment is from the setting position of the joint loss to the end of the fiber.
(122) In step 403, if the fiber is present as a segment, respective power variables in the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression for the first segment of the fiber being weighted by a weighting value
(123)
solving the out-of-band ASE power value; and substituting the out-of-band ASE power value into a relational expression between the out-of-band ASE power and a 0 km-equivalent joint loss to obtain the 0 km-equivalent joint loss;
(124) Wherein in other embodiments, the 0 km-equivalent joint loss is also marked as Att.sub.point.
(125) In step 404, if the fiber is present as two segments, respective power variables in the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression for the first segment of the fiber being weighted by a weighting value
(126)
and respective power variables for the second segment being weighted by a weighting value that is a product of a final value of the power variables in the first segment multiplying
(127)
solving the out-of-band ASE power value according to the weighted relational expressions of the first and second segments; and substituting the out-of-band ASE power value into the relational expression between the out-of-band ASE power and the 0 km-equivalent joint loss to obtain the 0 km-equivalent joint loss.
(128) Wherein the relational expression between the out-of-band ASE power and the 0 km-equivalent joint loss is: Pointloss=(ASE.sub.out-of-band−k*P.sub.pump−b)/(k+1), k is a tilt of the linear relationship, b is an intercept of the straight line. In the embodiment of the present disclosure, it corresponds to a reuse of calculation formula for calculating the total joint loss involved in Embodiment 1, however, the difference is that the computing environment set up by the embodiment of the present disclosure is only for a method for determining the 0 km-equivalent joint loss of a fiber node (i.e. a distance between the joint and the pump source), at this time, impacts of fiber attenuation coefficients and fiber mode field diameters will be eliminated, i.e. Pointloss at this time is the 0 km-equivalent joint loss of fiber node.
(129) Wherein solving the relational expression between the out-of-band ASE power and the 0 km-equivalent joint loss further comprises:
(130) selecting a specified pump laser pump1, calculating out-of-band ASE detection values corresponding to each output power of the pump1 when the joint loss Pointloss is 0, and solving corresponding parameters k and b in a formula 0=ASE.sub.out-of-band−k*P.sub.pump−b according to the out-of-band ASE detection values corresponding to each output power; then presenting the joint loss Pointloss as Pointloss=(ASE.sub.out-of-band−k*P.sub.pump−b)/(k+1).
(131) The embodiment of the present disclosure provides an implementation method for calculating a 0 km-equivalent joint loss when a joint loss is set at a specific position. Through the method provided by the embodiment of the disclosure, a curve diagram as shown in
(132) In the embodiment of the present disclosure, the pump transmission power relational expression further comprises:
(133) a first pump light transmission power relational expression:
(134)
where α.sub.0 is a transmission loss of a wavelength corresponding to the pump P.sub.0,
(135)
is a Raman gain coefficient from the pump P.sub.0 to the pump P.sub.k (or from the pump P.sub.0 to the signal P.sub.k),
(136) a second pump light transmission power relational expression:
(137)
where α.sub.i is a transmission loss of a wavelength corresponding to the pump
(138)
is a gain coefficient between the pump P.sub.i and the pump
(139)
is gain coefficient between the pump P.sub.i and the pump or signal P.sub.k (or the pump P.sub.i and the signal P.sub.k);
(140) weighting the power variables in the pump transmission power relational expression by a weighting value
(141)
comprising replacing the variables P.sub.0(Z) and P.sub.i(Z) at a right side of the first and second pump light transmission power relational expressions by
(142)
respectively. The transformed formula are as follows:
(143)
(144) In the embodiment of the present disclosure, the signal transmission power relational expression further comprises:
(145)
where α.sub.n is an attenuation coefficient of the n-th signal wavelength
(146)
is a gain coefficient between the j-th pump and the n-th signal, P.sub.n is power of the n-th signal, P.sub.j(z) is power of the j-th signal or pump with a wavelength less than the n-th signal wavelength;
(147) weighting the power variables in the signal transmission power relational expression by a weighting value
(148)
comprising replacing the variable P.sub.n(z) at a right side of the signal transmission power relational expression by
(149)
The transformed formula is as follows:
(150)
(151) In the embodiment of the present disclosure, the out-of-band ASE power relational expression further comprises:
(152)
where P.sub.ASE(z) is the out-of-band ASE power of the frequency v varying with the distance z, α.sub.ASE is an attenuation coefficient of the out-of-band ASE at a certain frequency,
(153)
is a gain coefficient from the i-th pump to the out-of-band ASE of the frequency v, h is the Planck's constant, v is the frequency of the out-of-band ASE, K is the Boltzmann constant, T is the ambient temperature, Δv is the frequency shift from the pump light frequency to the out-of-band ASE, P.sub.i(z) is the power value of the i-th pump;
(154)
(155) weighting the power variables in the out-of-band ASE power relational expression by a weighting value
(156)
comprising replacing the variable P.sub.n(Z) at a right side of the out-of-band ASE power relational expression by
(157)
The transformed formula is as follows:
(158)
(159) In the embodiment of the present disclosure, the 0 km-equivalent joint loss of joints set at different positions may be solved through steps 401-404; however, it can be found from the related description of Embodiment 1 and the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression, that impact of the fiber length and the fiber attenuation coefficient are simultaneously involved in each relational expression, therefore, in order to improve accuracy of calculation results of the embodiment of the present disclosure, preferably, the fiber attenuation coefficient in the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression is set as a calibration value (for example: α.sub.0 is set as 0.25 dB/km, α.sub.i is set as 0.25 dB/km, α.sub.n is set as 0.2 dB/km, and α.sub.ase is set as 0.2 dB/km); the fiber length is set to be larger than 100 km.
(160) In the embodiment of the present disclosure, the solving the 0 km-equivalent joint loss further comprises: in the above formulas (I), (II), (III) and (IV), formulas (I) and (II) take power change of each pump laser on the transmission line as the subject of solution, which reflects relational expressions that optical power of each pump laser is affected by other pump lasers and signal optical power on the transmission line; and formula (III) takes power change of signal light on the transmission line as the subject of solution, which reflects a relational expression that signal optical power is affected by other pump lasers and signal optical power on the transmission line; the final formula (IV) takes the out-of-band ASE power as the subject of solution, which reflects the result that the out-of-band ASE is affected by optical power of each pump laser, and which directly relates to formulas (I) and (II), however, formula (III) also affects parameter factor of signal optical power in formulas (I) and (II), therefore, in the embodiment of the present disclosure, the out-of-band ASE power is solved based on the correlated relationship between the above formulas (I), (II), (III), and (IV). Thus, the out-of-band ASE power may be substituted into the relational expression between the out-of-band ASE power and the 0 km-equivalent joint loss, specifically, Pointloss=(ASE.sub.out-of-band−k*P.sub.pump−b)/(k+1), where k is a tilt of the linear relationship, b is an intercept of the straight line. In a case where there is only one variable Pointloss, the 0 km-equivalent joint loss is solved.
(161) In the embodiment of the present disclosure, one of the effective means for solving the above obtained pump transmission power relational expression, signal transmission power relational expression and out-of-band ASE power relational expression to obtain the 0 km-equivalent joint loss (i.e. how to solve the out-of-band ASE power according to the above formulas (I), (II), (III), (IV)) is completed by Matlab, specifically, the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression are reformed into a format supported by a numerical solution of ordinary differential equation in Matlab;
(162) The initial power and/or the termination power of each frequency light is established based on the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression. That is, each boundary value is established, for a backward pump, the initial value of pump power is the value of terminal end of fiber (Z=L), i.e. the setting power of each pump laser; the initial value of signal light and ASE is the value of starting end of fiber (Z=0). During calculation, both of the attenuation coefficient and the optical power are all linear mW values; a numerical solution of a differential equation is calculated by the fourth-order Runge-Kutta algorithm or a boundary values method for solving differential equation in Matlab. In the specific calculation process, the number of pump light power variable and signal light power variable in the above formulas will usually be set according to the number of Raman pump lasers and signal light set in the specific environment, further, when calculating with Matlab, a set of initial values whose number is equal to the number of variables need to be substituted as the input parameter value of fourth-order Runge-Kutta algorithm, thus it further relies on the ordinary differential equation numerical solution of the above formulas, i.e. proposed initial signal optical power and initial Raman pump laser power.
Embodiment 4
(163) The embodiment of the present disclosure provides a method for determining a 0 km-equivalent joint loss of fiber attenuation coefficient in a Raman fiber amplifier. The determining method proposed in the embodiment of the present disclosure may be operated by a third-party computer, and the obtained data result may be imported into control unit 3 involved in each embodiment of the present disclosure, and the determining method described in the embodiment of the present disclosure may also be directly performed by the control unit 3, which is not particularly limited here. As described in
(164) In step 501, obtaining a pump transmission power relational expression, a signal transmission power relational expression, and an out-of-band ASE power relational expression.
(165) In step 502, weighting each power variable in the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression by a weighting value
(166)
respectively;
(167) In step 503, adjusting a fiber attenuation coefficient in the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression m times according to a preset step (e.g., increase or decrease 0.01 dB/km, 0.02 dB/km, 0.03 dB/km relative to the calibration fiber loss α.sub.v for a total of m times, where m is a natural number), and solving out-of-band ASE power value from the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression every time the fiber attenuation coefficient is adjusted; substituting the out-of-band ASE power value into a relational expression between the out-of-band ASE power and a 0 km-equivalent joint loss to obtain the 0 km-equivalent joint loss; and further calculating 0 km-equivalent joint loss for the other m−1 times of adjustments, thereby obtaining m pairs of fiber attenuation coefficient and corresponding 0 km-equivalent joint loss.
(168) The relational expression between the out-of-band ASE power and the 0 km-equivalent joint loss is as follows: Pointloss=(ASE.sub.out-of-band−k*P.sub.pump−b)/(k+1), where k is a tilt of the linear relationship, b is an intercept of the straight line. For description of reusing this formula, similar to the description in Embodiment 3, the difference is that what is equivalent to Pointloss at this time is a 0 km-equivalent joint loss caused by the fiber attenuation coefficient.
(169) The embodiment of the present disclosure provides a method for calculating a 0 km-equivalent joint loss caused by different fiber attenuation coefficients. Based on the method provided by the embodiment of the disclosure, after setting sufficient joint loss positions and obtaining corresponding 0 km-equivalent joint loss under each set joint loss coefficient, a curve diagram as shown in
(170) For obtaining the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression involved in the embodiment of the present disclosure may refer to relevant description in Embodiment 4, and will not be described in detail here.
(171) In the embodiment of the present disclosure, results of 0 km-equivalent joint loss caused by different fiber attenuation coefficients may be solved through steps 501-503; however, it may be found from the related description of Embodiment 1 and the above form of the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression, that impact of fiber length and joint loss caused by distance between the joint and the pump source are simultaneously involved in each relational expression, therefore, in order to improve accuracy of calculation result of the embodiment of the present disclosure, preferably, the fiber joint loss in the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression is set to 0; the fiber length is set to be larger than 100 km.
(172) Wherein the fiber joint loss in the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression setting as 0, is specifically represented that the above formulas (I), (II), (III), and (IV) are transformed again as follows when Pointloss is 0:
(173)
(174) Then, the power value of the out-of-band ASE corresponding to respective fiber attenuation coefficient may be solved by formulas (I′), (II′), (III′), and (IV′) with reference to the solving method similar to the solution of Matlab software in Embodiment 3, and substituted into Pointloss=(ASE.sub.out-of-band−k*P.sub.pump−b)/(k+1), and the 0 km-equivalent joint loss is solved.
(175) In the implementation process of the embodiment of the present disclosure, the reason why the weighting value
(176)
is introduced in the above step 502 is to explain the presentation form of the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression when calculating the 0 km-equivalent joint loss from the level of principle; and it is known from the above transformed formulas (I′), (II′), (III′), and (IV′) that after the joint loss impact factor caused by the distance between the joint and the pump source is strictly peeled off, the above weighting value
(177)
actually does not work, therefore, combined with the embodiment of the present disclosure, there is also a preferred implementation mode, i.e. omitting the weighting operation in step 502, that is to say, implementing the method described in the embodiment of the present disclosure through step 501 and step 503, at this time, it may not be necessary to perform the operation of setting the fiber joint loss in the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression in the above preferred solution to 0.
Embodiment 5
(178) The embodiment of the present disclosure provides a method for determining a maximum gain impact factor corresponding to a fiber length in a Raman fiber amplifier, which may be used to support the determination of the relationship between a fiber length and a gain impact factor involved in other related embodiments of the present disclosure. As shown in
(179) In step 601, obtaining a pump transmission power relational expression, a signal transmission power relational expression and an out-of-band ASE power relational expression, and a plurality of fiber lengths for relational expressions corresponding to the impact factor to be solved; selecting each fiber length and configuring it into the respective relational expression to solve the impact factor as follows:
(180) In step 602, setting an initial pump value in the above relational expressions to 0 and an initial power of the signal light to P1, and obtaining the signal power P.sub.(L-pump off) at the fiber end according to the above relational expressions.
(181) The power directly solved from the above relational expressions is a linear unit mW, and the signal power P.sub.(L-pump off) is obtained by conversion from mW to dBm, so as to subsequently perform formula on impact factors.
(182) In that case of providing the initial pump value, the initial signal value and the initial ASE value, the initial power of forward ASE is 0.
(183) In step 603, setting the initial value of the pump power to a preset value P2, and obtaining the signal power P.sub.(L-pump on) at the fiber end and the out-of-band ASE power P.sub.ASE from the above relational expressions.
(184) The power directly solved according to the above relational expression is a linear unit mW, and the signal power P.sub.(L-pump on) at the fiber end and the out-of-band ASE power P.sub.ASE is obtained by a conversion from mW to dBm, so as to subsequently perform the formula calculation for solving impact factors.
(185) In step 604, the impact factor A4 caused by the fiber length being (P.sub.(L-pump on)−P.sub.(L-pump off)−IL)/P.sub.max_calibration where the inherent insertion loss of the amplifier is IL, P.sub.max_calibration is the calibrated maximum gain of the Raman fiber amplifier, and P.sub.(L-pump on), P.sub.(L-pump off) and P.sub.max_calibration are in dBm.
(186) The embodiment of the present disclosure provides an implementation method for calculating a maximum gain impact factor under different fiber lengths. Depending on the method provided by the embodiment of the disclosure, a curve diagram as shown in
(187) In the implementation process of the embodiment of the present disclosure, in order to avoid the impact of fiber attenuation coefficient (i.e. the 0 km-equivalent joint loss of fiber attenuation coefficient) on the relationship between the fiber length and the impact factor—the subject concerned in the embodiment of the present disclosure, preferably, the fiber attenuation coefficient in the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression is set to a calibration value. For example: α.sub.0 is set to 0.25 dB/km, α.sub.i is set to 0.25 dB/km, α.sub.n is set to 0.2 dB/km, and α.sub.ase is set to 0.2 dB/km. It should be emphasized that the weighting value
(188)
is not introduced into each relational expression in the embodiment of the present disclosure, therefore, there is no impact of the 0 km-equivalent joint loss caused by the distance between the joint and the pump source on the calculation process.
(189) The embodiment of the present disclosure also provides an effective means for solving a signal power and an out-of-band ASE power from the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression, specifically:
(190) reforming the pump transmission power relational expression, the signal transmission power relational expression and the out-of-band ASE power relational expression into a format supported by a numerical method of ordinary differential equation in Matlab;
(191) calculating a numerical solution of the differential equation by the fourth-order Runge-Kutta algorithm or a boundary value method in Matlab.
(192) Further, the embodiment of the present disclosure also provides the above pump transmission power relational expression, signal transmission power relational expression and out-of-band ASE power relationship.
(193) For example, the pump transmission power relational expression further comprises:
(194) a first pump light transmission power relational expression:
(195)
(196) where α.sub.0 is a transmission loss of a wavelength corresponding to the pump
(197)
is a Raman gain coefficient from the pump P.sub.0 to the pump or signal P.sub.k.
(198) a second pump light transmission power relational expression:
(199)
where α.sub.i is a transmission loss of a wavelength corresponding to the pump
(200)
is a gain coefficient between the pump P.sub.i and the pump
(201)
is a gain coefficient between the pump P.sub.i and the pump or signal P.sub.k.
(202) For example, the signal transmission power relational expression further comprises:
(203)
where α.sub.n is an attenuation coefficient of the n-th signal wavelength
(204)
is a gain coefficient between the j-th pump and the n-th signal, P.sub.n is power of the n-th signal, P.sub.j(z) is power of the j-th signal or pump with a wavelength less than the n-th signal wavelength.
(205) For example, the out-of-band ASE power relational expression further comprises:
(206)
where P.sub.ASE(z) is the out-of-band ASE power of the frequency v varying with the distance z, α.sub.ASE is an attenuation coefficient of the out-of-band ASE at a certain frequency,
(207)
is a gain coefficient from the i-th pump to the out-of-band ASE of the frequency v, h is the Planck's constant, v is the frequency of the out-of-band ASE, K is the Boltzmann constant, T is the ambient temperature, Δv is a frequency shift from the pump light frequency to the out-of-band ASE, P.sub.i(z) is the power value of the i-th pump.
(208) In the embodiment of the present disclosure, a determining method is also provided for the calibrated maximum gain G.sub.max_calibration involved in step 604, and further comprises:
(209) establishing a relational expression between a gain tilt and a maximum gain through collecting maximum gain values of a Raman fiber amplifier under respective gain tilt in advance;
(210) and looking up the above established relational expression between the gain tilt and the maximum gain by a gain tilt of a current fiber transmission line to obtain a calibrated maximum gain G.sub.max_calibration.
(211) wherein the establishing a relational expression between a gain tilt and a maximum gain comprises:
(212) when Tilt<Tilt.sub.turning point,
G.sub.max_calibration=k.sub.01*Tilt+b.sub.01;
(213) when Tilt≥Tilt.sub.turning point,
G.sub.max_calibration=k.sub.02*Tilt+b.sub.02;
(214) and looking up the above established relational expression between the gain tilt and the maximum gain by a gain tilt of a current fiber transmission line to obtain a calibrated maximum gain G.sub.max_calibration, further comprises:
(215) substituting a Tilt setting value into corresponding one of the above two formulas to obtain the calibrated maximum gain G.sub.max_calibration.
Embodiment 6
(216) The embodiment of the present disclosure will describe how to implement the method proposed in Embodiment 1 and Embodiment 2 of the present disclosure in specific application scenario combined with the related module units in
(217) Specifically, as shown in
(218) Step 1: electrifying a Raman pump module, during the electrification of the Raman pump module, a certain pump laser in the pump laser group 1 or the pump laser group 2 being operating as an OTDR light source, or driving an additional laser 14 to operate, modulated signals 4 generated by control unit 3 having different pulse widths, control unit 3, modulated signals 4, optical circulator 5 and photodetector 6 constituting OTDR. Checking whether signal power is larger than a LOS threshold, when it is larger than the LOS threshold, recording stable signal power P.sub.INU without opening the Raman pump laser. OTDR being turned on to check the transmission performance of a fiber line, and OTDR firstly testing three parameters of a fiber transmission loss, a joint loss and a transmission fiber length of a transmission fiber, and data being stored in control unit 3 after the test is completed. Control unit 3 equivalizing a joint loss Pointloss at different positions of fiber to a 0 km-equivalent joint loss Pointloss, recording as Att.sub.point, specifically, establishing, in control unit 3, a table of a 0 km-equivalent joint loss varying a position in the fiber, and obtaining the 0 km-equivalent joint loss for a positions in the fiber by looking up the table and interpolation, as shown in
(219) Step 2: turning off the pump laser tested as OTDR in step 1, and recording the stable unamplified signal power P.sub.INU without opening the Raman pump laser, turning on the pump laser to a low power level condition to enable detector 11 to detect out-of-band ASE optical power and prevent a fiber end face from being damaged by excessive pump power, at the same time, obtaining a total joint loss Pointloss of the transmission line by using the out-of-band ASE, the total joint loss Pointloss being recorded as Att.sub.Toal; the above low pump power condition referring to the used pump power being not large, for example, tens of mW, or about 100 mW, and the reason for selecting low pump power being mainly safety consideration, i.e. when the pump power is too large, it is easy to burn the end face of fiber or cause other dangerous situation. firstly setting pump to a low power condition during opening process, under this pump power, generating out-of-band ASE power and recording it as P.sub.ASE-real and its unit being dBm, recording the low pump power used to calculate joint loss as P.sub.pump and its unit being dBm, and the total joint loss being recorded as Att.sub.Toal, then:
Att.sub.Toal=(P.sub.ASE-real−b−k*P.sub.pump)/(k+1),
where P.sub.pump is power of a pump laser, k is a tilt of the linear relationship, b is an intercept of the straight line.
(220) Step 3: control unit 3 calculating a joint loss Pointloss caused by mode field diameter or effective area factor and recording as Att.sub.Aeff by control unit 3; and
Att.sub.Aeff=Att.sub.Toal−Att.sub.point−Att.sub.coefficient (1)
(221) Step 4: determining an actual maximum gain that may be achieved by the Raman pump module by combining with the 0 km joint loss Att.sub.point equivalent to a joint loss at different positions, the 0 km-equivalent joint loss value Att.sub.coefficient of fiber loss system, the 0 km-equivalent joint loss value Att.sub.Aeff of the fiber mode field and the transmission fiber length. That is, determining the maximum gain G.sub.max_factual that may be achieved by the Raman fiber amplifier according to the actual condition of different application environments.
(222) Specifically, different types of joint loss, such as an equivalent joint loss Att.sub.point introduced by nodes at different positions of fiber, an equivalent joint loss Att.sub.coefficient introduced by the fiber loss coefficient, and an equivalent joint loss Att.sub.aeff introduced by the fiber effective area, have different impact factors on the maximum gain, and establishing in control unit 3 a table of reduced ratio data or functional relationship between an equivalent joint loss Att.sub.point equivalent to a joint loss at different positions of the fiber, an equivalent joint loss Att.sub.coefficient introduced by the fiber loss coefficient, and an equivalent joint loss Att.sub.aeff introduced by the effective fiber area and the maximum gain that can actually be achieved is implemented by looking up table or interpolation or function fitting during the control process. Wherein the 0 km-equivalent joint loss Att.sub.point of the fiber joint loss and the 0 km-equivalent joint loss Att.sub.coefficientt of the fiber loss coefficient may be larger than 0, or may be less than 0 or equal to 0, while the 0 km-equivalent joint loss Att.sub.Aeff of mode field diameter is negative, therefore, the impact of ratio of the actual maximum Raman gain to the calibrated maximum Raman gain at different equivalent joint loss is shown in
(223)
(224) Before calculating the actual maximum gain G.sub.max_factual that may be actually achieved, it is usually necessary to determine the calibrated maximum gain G.sub.max_calibration of a current fiber transmission line according to a ratio relationship between the gain tilt Tilt and the calibrated maximum gain; and to determine the actual maximum gain G.sub.max_factual that may be actually achieved by the Raman fiber amplifier, according to the calibrated maximum gain G.sub.max_calibration, and the impact of the distance between the joint and the pump source, the fiber loss coefficient, the fiber mode field diameter and the fiber length on the calibrated maximum gain G.sub.max_calibration.
(225) In a case where there is no influence of different types of joint loss (including a fiber loss coefficient, a distance between a joint and a pump source and a fiber mode field diameter) and a fiber length, the maximum gain of a Raman fiber amplifier under different gain tilts is shown in
(226) Therefore, G.sub.max_calibration corresponds to two different groups of straight lines before and after the turning point,
(227) when Tilt<Tilt.sub.turning point,
G.sub.max=k.sub.01*Tilt+b.sub.01; (2)
(228) When Tilt≥Tilt.sub.turning point,
G.sub.max=k.sub.02*Tilt+b.sub.02; (3)
(229) where Tilt represents a gain tilt; k.sub.01 and k.sub.02 respectively represent tilts to be calibrated, and b.sub.01 and b.sub.02 respectively represent intercepts to be calibrated.
(230) Considering impact of different types of equivalent joint loss and fiber lengths on the maximum gain, assuming that impact factors of the joint loss Att.sub.point, the equivalent joint loss Att.sub.coefficient of fiber loss coefficient, the equivalent joint loss Att.sub.Aeff of effective fiber area and a fiber length x on the maximum gain are respectively A.sub.1, A.sub.2, A.sub.3, A.sub.4, the overall impact on the maximum gain is:
A=A.sub.1*A.sub.2*A.sub.3*A.sub.4 (4)
(231) and the maximum gain that may actually be achieved is:
G.sub.max_factual=G.sub.max_calibration*A (5)
(232) where G.sub.max_calibration is the calibrated maximum of the Raman fiber amplifier, G.sub.max_factual is the maximum gain that may actually be achieved under various impact of loss and attenuation in actual application environment.
(233) Step 5: If the setting gain G.sub.setting is larger than the actual maximum G.sub.max_factual that may actually be achieved, substituting the maximum gain G.sub.max_factual (that may be actually achieved) into formula (6) and formula (7), and performing the actual maximum gain G.sub.max_factual that may be actually achieved. Wherein calculating G.sub.max_factual as a specific value of parameter G in Formula (6) and Formula (7). Otherwise, proceeding to step 9.
(234) Specifically, the linear relationship among the out-of-band ASE, the gain and the gain tilt:
ASE.sub.out-of-band+ΔASE=k.sub.1*G+k.sub.2*Tilt+b.sub.1+Att.sub.point (6)
(235) where ASE.sub.out-of-band is optical power of the out-of-band ASE, i.e. P.sub.out-of-band ASE, k.sub.1 is a tilt factor of the linear relationship between the out-of-band ASE optical power (its unit is dBm) and the amplifier gain G (its unit is dB), k.sub.2 is a tilt factor of the linear relationship between the out-of-band ASE optical power (its unit is dBm) and the gain tilt Tilt (its unit is dB), b1 is an intercept; the k.sub.1, k.sub.2 and b.sub.1 are all obtained by calibration, and ΔASE is a correction term.
(236) The Output power ratio relationship of Raman pump laser group:
p.sub.1/p.sub.2=k.sub.3*G+k.sub.4*Tilt+b.sub.2 (7)
(237) p.sub.1 is the output power of Raman pump laser group 1, p.sub.2 is the output power of Raman pump laser group 2, k.sub.3 is a tilt factor linearly related to the amplifier gain G (its unit is dB), and k.sub.4 is a tilt factor linearly related to the gain tilt Tilt (its unit is dB), b.sub.2 is an intercept, and k.sub.3, k.sub.4 and b.sub.2 are all obtained by calibration.
(238) G in the above formula (6) and formula (7) is the target gain, i.e. the setting gain G.sub.setting that may actually be achieved.
(239) Step 6: calculating signal power P.sub.signal by using the linear relationship among the out-of-band ASE.sub.out-of-band, the in-band ASE.sub.in-band and the gain tilt. Specifically, the in-band ASE.sub.in-band power is calculated by the following formula (8).
ASE.sub.in-band=k.sub.5*ASE.sub.out-of-band+k.sub.6Tilt+(k.sub.5−1)*Att.sub.point+b (8)
(240) where ASE.sub.in-band is the ASE optical power within an operating bandwidth and its unit is dBm, ASE.sub.out-of-band is the ASE optical power outside the operating bandwidth and its unit is dBm, and k.sub.5 is a ratio coefficient of the linear relationship between the out-of-band ASE.sub.out-of-band and the in-band ASE.sub.in-band, k.sub.6 is an impact factor on a relationship between the original in-band ASE.sub.in-band and the out-band ASE.sub.out-of-band under different gain tilts, and b is an intercept.
(241) Step 7: Detecting total power P.sub.total by PD detector 12, where the total power P.sub.total detected by PD detector 12 includes two portions, one portion is the signal power P.sub.signal, the other portion is the in-band ASE.sub.in-band power whose unit is in mW, and obtaining the signal power P.sub.signal, its unit is in dBm, by subtracting the calculated ASE.sub.in-band from the total power P.sub.total. The specific calculation formula is as follows:
P.sub.signal=10*log.sub.10(P.sub.total−10{circumflex over ( )}(ASE.sub.in-band/10)) (9)
(242) obtaining a current actual gain G.sub.factual of the Raman fiber amplifier by subtracting the stable signal power P.sub.INU before the Raman pump laser is turned on from the obtained signal power P.sub.signal.
G.sub.factual=P.sub.signal−P.sub.INU (10)
(243) Adjusting control parameter of the Raman pump module by Control unit 3 to raise its gain to G.sub.factual so as to complete gain control of the Raman fiber amplifier.
(244) Recording the gain value G obtained by formula (6) and formula (7) as G.sub.operation, and calculating a gain error by control unit 3.
ΔG=G.sub.operation−G.sub.factual (11)
(245) If ΔG exceeds the gain control accuracy requirement, substituting ΔG+G.sub.factual into formula (6) and formula (7) in step 5 as a new gain G control quantity to perform iterative calculation and implement feedback control, thereby achieving control accuracy requirement.
(246) Step 8: if the setting gain G.sub.setting is less than the maximum gain G.sub.max_factual (that may be actually achieved), substituting the setting gain G.sub.setting into formula (6) and formula (7) and obtaining the following two formulas:
ASE.sub.out-of-band+ΔASE=k.sub.1*G.sub.setting+k.sub.2*Tilt+b.sub.1+Att.sub.point
p.sub.1/p.sub.2=k.sub.3*G.sub.setting+k.sub.4*Tilt+b.sub.2
(247) Step 9: calculating the signal power P.sub.signal with the linear relationship among the out-of-band ASE.sub.out-of-band, the in-band ASE.sub.in-band and the gain tilt. Specifically, the in-band ASE.sub.in-band power is calculated by the formula (8).
(248) Step 10: detecting the total power P.sub.total by PD detector 12, obtaining the signal power P.sub.signal, its unit is in dBm, by subtracting the calculated ASE.sub.in-band from the total power P.sub.total (The specific calculation formula is shown as formula (9)), and calculating the current actual gain G.sub.factual of the Raman fiber amplifier (The specific calculation formula is shown as formula (10)), where the total power P.sub.total detected by PD detector 12 includes two portions, one portion is the signal power P.sub.signal, the other portion is the in-band ASE.sub.in-band power whose unit is in mW.
(249) Adjusting control parameters of the Raman pump module by control unit 3 to raise its gain to G.sub.factual so as to complete gain control of the Raman fiber amplifier.
(250) Recording the gain value G obtained by formula (6) and formula (7) as G.sub.operation, and calculating a gain error by control unit 3.
ΔG=G.sub.operation−G.sub.factual (11)
(251) If ΔG exceeds the gain control accuracy requirement, substituting ΔG+G.sub.factual as a new gain G control quantity into formula (6) and formula (7) in step 5 to perform iterative calculation and implement feedback control, thereby achieving the control accuracy requirement.
(252) It should be noted that the contents such as information interaction and execution process and the like between the modules and units of the above apparatus and the system are based on the same concept as the processing method of the embodiments of the present disclosure, and the specific contents may be referred to the description in the method embodiment of the present disclosure and will not be repeated here.
(253) Those skilled in the art may understand that all or part of the various methods of the embodiments of the present disclosure may be completed by a program to instruct related hardware, and the program may be stored in a computer readable storage medium, and the storage medium may include read only memory (ROM, Read Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and so on.
(254) What is described above is only a preferred embodiment of the present disclosure, and is not intended to limit the present disclosure, and any modifications, equivalent substitutions and improvements made within the spirit and principles of the present disclosure should be included within the scope of protection of the present disclosure.