Method for realizing precise target gain control for hybrid fibre amplifier, and hybrid fibre amplifier

Abstract

A method for realizing precise gain control for a hybrid fibre amplifier, and a hybrid fibre amplifier, in which by an erbium-doped fibre amplifier firstly outputting a constant power, a comparable source signal optical power is provided for a raman fibre amplifier of a next stage. A feedback for the gain control may be formed by comparing a source signal optical power calculated after starting pumping of the Raman fibre amplifier and a source signal optical power detected after pumping stops, thereby greatly improving gain control precision of the Raman fibre amplifier. Moreover, the erbium-doped fibre amplifier parts of all the hybrid fibre amplifiers may simultaneously output a constant optical power, and the Raman amplifier parts of all the hybrid fibre amplifiers may simultaneously start calibration, so that the time for starting operation of the entire system may be improved greatly.

Claims

1. A method for realizing precise target gain control of a hybrid fibre amplifier, being characterized in comprising the following steps: Step 1: controlling an erbium-doped fibre amplifier of the hybrid fibre amplifier firstly to output light with a constant power P1 when the hybrid fibre amplifier starts pumping; Step 2: after the erbium-doped fibre amplifier outputs the constant power for a period of time t1, controlling a Raman fibre amplifier of the hybrid fibre amplifier to detect a source signal optical power S1 and an out-of-band ASE power Source_ASE1 contained in the source signal light; Step 3: reading a target gain G1 from a control unit part and a relationship between the gain and the out-of-band ASE obtained by calibration to calculate a target ASE power P.sub.G1_ASE1, and calculating a target out-of-band ASE power Target_ASE_1 compensated by the source ASE: Target_ASE_1=P.sub.G1_ASE1+Source_ASE1*G1; Step 4: controlling the Raman fibre amplifier to start pumping when it is determined that the source signal optical power S1 detected by the Raman fibre amplifier becomes stable, and reading a detection value of the out-of-band ASE power in real-time; Step 5: comparing the detection value of the out-of-band ASE power read in Step 4 with the Target_ASE_1, and stopping adjustment of the pumping power when the two values are equal to each other; Step 6: when the pumping power of the Raman fibre amplifier becomes stable, calculating a source signal optical power S2 after starting pumping, and comparing S1 with S2 to calculate a delta Gain ΔG=S2−S1; if the delta Gain meets an accuracy requirement, proceeding to Step 8 directly; and if the delta Gain does not meet the accuracy requirement, proceeding to Step 7; Step 7: compensating the delta Gain to the target gain to obtain G2=G1−ΔG; repeating Step 3 to calculate a new target out-of-band ASE power ASE3; and repeating Step 4, Step 5 and Step 6 in this order; Step 8: controlling the erbium-doped fibre amplifier to start pumping according to a preset gain requirement so as to achieve a rated control gain of the hybrid fibre amplifier when the pumping power of the Raman fibre amplifier becomes stable.

2. A hybrid fibre amplifier for realizing a precise target gain control, being characterized in comprising a Raman fibre amplifier part (1), an erbium-doped fibre amplifier part (9), and a control unit part (10); the Raman fibre amplifier part including a pump signal combiner (2), a Raman pump laser bank (11) connected to a pumping input end of the pump signal combiner (2), a first optical splitting coupler (3) connected to a signal output end of the pump signal combiner (2), a first photodetector (4) connected to a low transmission end of the first optical splitting coupler (3), an out-of-band ASE filter (5) connected to a high transmission end of the first optical coupler (3), a second photodetector (6) connected to an out-of-band light output end of the out-of-band ASE filter (5), a second optical splitting coupler (7) connected to a signal light output end of the out-of-band ASE filter (5), a third photodetector (8) connected to a low transmission end of the second optical splitting coupler (7), a high transmission end of the second optical splitting coupler (7) serving as an output end of the Raman fibre amplifier part, and the output end of the Raman fibre amplifier part being connected with an input end of the erbium-doped fibre amplifier part (9); wherein the low transmission end for the first coupler and the second coupler is tap output with low transmission, and the high transmission end for the first coupler and the second coupler is tap output with high transmission as compared to the low transmission end; the control unit part (10) being connected with the Raman pump laser bank (11), the first photodetector (4), the second photodetector (6), the third photodetector (8), and the erbium-doped fibre amplifier part (9), respectively, wherein the first photodetector of the Raman fibre amplifier is used for detecting a source signal optical power S1 and an out-of-band ASE power Source ASE1 contained in the source signal light when the Raman stops pumping.

3. The hybrid fibre amplifier for realizing a precise target gain control according to claim 2, being characterized in that: the control unit part (10) includes a pump laser output control unit (20), a signal light and out-of-band ASE detecting and storing unit (21), a gain and out-of-band ASE calculating unit (22), and an erbium-doped fibre amplifier gain control unit (23).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a structure of a hybrid fibre amplifier of the present invention.

(2) FIG. 2 is a schematic diagram illustrating configuration of hybrid fibre amplifiers used in a practical system.

(3) FIG. 3 is a schematic structural diagram of a control unit part.

(4) In the drawings: 1: Raman fibre amplifier part; 2: Pump signal combiner; 3: First optical splitting coupler; 4: First photodetector; 5: Out-of-band ASE filter; 6: Second photodetector; 7: Second optical splitting coupler; 8: Third photodetector; 9: Erbium-doped fibre amplifier part; 10: Control unit part; 11: Raman pump laser bank; 12: Erbium-doped fibre power amplifier; 13: First transmission fibre; 14: First hybrid fibre amplifier; 15: Second transmission fibre; 16: Third transmission fibre; 17: Second hybrid fibre amplifier; 18: EDFA pump laser bank; 19: Variable attenuator; 20: Pump laser bank control unit; 21: Signal light and out-of-band ASE detecting and storing unit; 22: Gain and out-of-band ASE calculating unit; 23: EDFA control unit

DETAILED DESCRIPTION

(5) In order to make purposes, technical solutions and advantages of the present invention more clear, this invention is further explained in combination with drawings and embodiments. It should be appreciated that the specific embodiments described here are only for explaining but not limiting the invention.

(6) The hybrid fibre amplifier provided in the present invention integrates a Raman fibre amplifier and an erbium-doped fibre amplifier, and by overall control of them, an accurate expected effect of the hybrid fibre amplifier is achieved.

(7) FIG. 1 illustrates a hybrid fibre amplifier for realizing precise gain control according to the present invention. FIG. 2 illustrates an application scenario of the hybrid fibre amplifier of the present invention.

(8) As shown in FIG. 1, the hybrid fibre amplifier includes a pump signal combiner (2), a pumping input end of the pump signal combiner is connected to a Raman pump laser bank (11), and a signal output end of the pump signal combiner (2) is connected to a common end of a first optical splitting coupler (3). A small end of the first optical splitting coupler (3) is connected to a first photodetector (4), and a large end of the first optical splitting coupler (3) is connected to a common end of an out-of-band ASE filter (5). An out-of-band light output end of the out-of-band ASE filter (5) is connected to a second photodetector (6), and a signal light output end of the out-of-band ASE filter (5) is connected to a common end of a second optical splitting coupler (7). A small end of the second optical splitting coupler (7) is connected to a third photodetector (8), and a large end of the second optical splitting coupler (7) serves as an output end of the Raman fibre amplifier part and is connected with the input end of the erbium-doped fibre amplifier part (9). The control unit part (10) is connected with the Raman pump laser group (11), the first photodetector (4), the second photodetector (6), the third photodetector (8), and the erbium-doped fibre amplifier parts (9), respectively.

(9) The erbium-doped fibre amplifier part (9) includes a pump laser bank (18) and a variable attenuator (19).

(10) As shown in FIG. 2, the depicted application scenario of the hybrid fibre amplifier includes an erbium-doped fibre power amplifier (12) and a plurality of hybrid fibre amplifiers sequentially connected, the hybrid fibre amplifiers are connected with each other by transmission fibres. The erbium-doped fibre amplifier part (9) of a previous hybrid fibre amplifier is connected with the Raman fibre amplifier part (1) of a next hybrid fibre amplifier by a transmission fibre. The erbium-doped fibre power amplifier (12) is connected to the first hybrid fibre amplifier (14) by a first transmission fibre (13), the first hybrid fibre amplifier (14) is connected to a second hybrid fibre amplifier (17) by a second transmission fibre (15), the second hybrid fibre amplifier (17) is connected to a third hybrid fibre amplifier by a third transmission fibre (16), and so on.

(11) As shown in FIG. 3, the control unit part (10) includes a pump laser output control unit (20), a signal light and out-of-band ASE detecting and storing unit (21), a gain and out-of-band ASE calculating unit (22), and an erbium-doped fibre amplifier gain control unit (23).

(12) The present invention provides a method for precisely controlling a target gain of the hybrid fibre amplifier comprising the following steps:

(13) Step 1: The control unit controls the EDFA part to output a constant output power, e.g. 6 dBm, when receiving a pumping start command; the output light is transmitted to the Raman fibre amplifier of the next stage through a transmission fibre, and at the same time, the Raman fibre amplifier in the present stage receives a constant optical power from the EDFA part in a hybrid fibre amplifier of a previous stage.

(14) Step 2: The first photodector of the Raman fibre amplifier detects a source signal optical power S1 and an out-of-band ASE power Source_ASE1 contained in the source signal light when the Raman stops pumping after a period of time t1.

(15) Step 3: A target gain G1 and a relationship between the gain and the out-of-band ASE are read to calculate a object ASE power G1_ASE1 and to calculate an object out-of-band ASE power Object_ASE_1 compensated by the source ASE, i.e., Object_ASE_1=G1_ASE1+Source_ASE1*G1.

(16) Step 4: When it is determined that the source signal optical power S1 detected by the Raman fibre amplifier becomes stable, the Raman fibre amplifier is controlled to start pumping, and a detection value of the out-of-band ASE power is read in real-time.

(17) Step 5: The detection value of the out-of-band ASE power read in Step 4 is compared with the Object_ASE_1, and when the two values are equal to each other, adjustment of pumping power stops.

(18) Step 6: When the pumping power of the Raman fibre amplifier becomes stable, the source signal optical power after starting pumping is calculated as S2 and compared with S1 to calculate a delta Gain, i.e., ΔG=S2−S1.

(19) Step 7: The target Gain G1 is compensated with the delta Gain to obtain G2, i.e., G2=G1−ΔG. Step 3 may be repeated to calculate a new object out-of-band ASE power ASE3. Then, Step 4 and Step 5 may be repeated.

(20) Usually when Step 5 is completed, pumping adjustment may stop and the gain controlled by the Raman fibre amplifier is relatively accurate. If a system error is relatively large or the system requires for a relatively high accuracy, Step 3 to Step 6 may be repeated after Step 7 is completed until the delta Gain meets the accuracy requirement of the system.

(21) Step 8: When the power of the Raman fibre amplifier becomes stable, the erbium-doped fibre amplifier is controlled to start pumping according to a preset gain requirement so as to achieve a rated control gain of the hybrid fibre amplifier.