BURST OPTICAL SIGNAL TRANSMISSION DEVICE AND BURST OPTICAL SIGNAL TRANSMISSION METHOD

Abstract

A burst optical signal transmission device which includes a light source for generating and outputting burst signal light, a light source driving circuit for outputting, to the light source, a driving signal for switching between an output time and a stop time of the burst signal light, based on a burst control signal, and a pre-emphasis circuit for outputting a pre-emphasis control signal for superimposing an additional signal for charging a capacitor included in the light source, onto the driving signal, at a timing in the vicinity of the beginning of the burst control signal.

Claims

1. A burst optical signal transmission device comprising: a light source for generating and outputting burst signal light; a light source driving circuit for outputting, to the light source, a driving signal for switching between an output time and a stop time of the burst signal light, based on a burst control signal; and a pre-emphasis circuit for outputting a pre-emphasis control signal for superimposing an additional signal for charging a capacitor included in the light source, onto a vicinity of a beginning of the driving signal.

2. The burst optical signal transmission device according to claim 1, wherein the vicinity of the beginning of the driving signal is a predetermined timing earlier than the beginning of the driving signal.

3. The burst optical signal transmission device according to claim 2, wherein the predetermined timing is a timing going back from the beginning of the driving signal, by a time required for charging the capacitor to a first predetermined rate.

4. The burst optical signal transmission device according to claim 3, wherein the predetermined timing is defined based on capacity of the capacitor, current to be flown into the capacitor, and voltage to be applied to the light source.

5. The burst optical signal transmission device according to claim 4, further comprising a current supplying unit for supplying, to the light source, such current as to cause charging of the capacitor to fall within a range being smaller than a second predetermined rate being lower than the first predetermined rate.

6. The burst optical signal transmission device according to claim 4, wherein the capacitor includes a bypass capacitor arranged in parallel with the light source or a parasitic capacitor underlying in the light source, or the bypass capacitor and the parasitic capacitor.

7. A burst optical signal transmission method executed by a burst optical signal transmission device for generating and outputting burst signal light using a light source, the method comprising: a pre-emphasis circuit outputting, when a light source driving circuit outputs, to the light source, a driving signal for switching between an output time and a stop time of the burst signal light, based on a burst control signal, a pre-emphasis control signal for superimposing an additional signal for charging a capacitor included in the light source, onto a vicinity of a beginning of the driving signal.

8. The burst optical signal transmission device according to claim 1, further comprising a current supplying unit for supplying, to the light source, such current as to cause charging of the capacitor to fall within a range being smaller than a second predetermined rate being lower than the first predetermined rate.

9. The burst optical signal transmission device according to claim 1, wherein the capacitor includes a bypass capacitor arranged in parallel with the light source or a parasitic capacitor underlying in the light source, or the bypass capacitor and the parasitic capacitor.

10. The burst optical signal transmission device according to claim 2, further comprising a current supplying unit for supplying, to the light source, such current as to cause charging of the capacitor to fall within a range being smaller than a second predetermined rate being lower than the first predetermined rate.

11. The burst optical signal transmission device according to claim 2, wherein the capacitor includes a bypass capacitor arranged in parallel with the light source or a parasitic capacitor underlying in the light source, or the bypass capacitor and the parasitic capacitor.

12. The burst optical signal transmission device according to claim 3, further comprising a current supplying unit for supplying, to the light source, such current as to cause charging of the capacitor to fall within a range being smaller than a second predetermined rate being lower than the first predetermined rate.

13. The burst optical signal transmission device according to claim 3, wherein the capacitor includes a bypass capacitor arranged in parallel with the light source or a parasitic capacitor underlying in the light source, or the bypass capacitor and the parasitic capacitor.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1 illustrates a configuration diagram of an external modulation type burst signal optical transmitter according to a related art.

[0035] FIG. 2 illustrates a configuration diagram of a burst control circuit in an external modulation type burst signal optical transmitter according to a first related art.

[0036] FIG. 3 illustrates a time chart in a control method for the external modulation type burst signal optical transmitter according to the first related art.

[0037] FIG. 4 illustrates a burst control circuit in an external modulation type burst signal optical transmitter according to a second related art.

[0038] FIG. 5 illustrates a time chart in a control method for the external modulation type burst signal optical transmitter according to the second related art.

[0039] FIG. 6 illustrates a configuration diagram of an external modulation type burst signal optical transmitter according to the present embodiment.

[0040] FIG. 7 illustrates a first configuration diagram of a burst control circuit in the external modulation type burst signal optical transmitter according to the present embodiment.

[0041] FIG. 8 illustrates a time chart in a control method for an external modulation type burst signal optical transmitter according to a first embodiment.

[0042] FIG. 9 illustrates a time chart in a control method for an external modulation type burst signal optical transmitter according to a second embodiment.

[0043] FIG. 10 illustrates an example of an evaluation result of a rising time of a burst optical signal according to a comparative example.

[0044] FIG. 11 illustrates an example of an evaluation result of a rising time of a burst optical signal according to an example.

[0045] FIG. 12 illustrates a second configuration diagram of a burst control circuit in the external modulation type burst signal optical transmitter according to the present embodiment.

[0046] FIG. 13 illustrates a third configuration diagram of a burst control circuit in the external modulation type burst signal optical transmitter according to the present embodiment.

DESCRIPTION OF EMBODIMENTS

[0047] Embodiments of the present invention will be described in detail below with reference to the drawings. In addition, the present invention is not limited to the following embodiments. These examples of the execution are mere exemplifications, and the present invention can be executed in a configuration in which various modifications and improvements have been made based on the knowledge of the one skilled in the art. In addition, in the specification and the drawings, constituent elements having the same signs indicate mutually same components.

First Embodiment of Invention

[0048] A control method for a 10 Gb/s level external modulator type burst optical signal transmitter according to a first embodiment of the present invention will be described in detail below based on FIGS. 6 to 8. FIG. 6 illustrates a configuration of a transceiver 1 in the 10 Gb/s level external modulator type burst signal optical transmitter being the first embodiment of the present invention. The transceiver 1 outputting burst signal light 10 includes an EML-TOSA 22, an EAM driving circuit 24, a burst-mode LD driving circuit 31, and a pre-emphasis circuit 35, and the EML-TOSA 22 includes a DFB-LD 13 and an EAM 23. Here, the transceiver 1 may function as a burst optical signal transmission device, the burst-mode LD driving circuit 31 may function as a light source driving circuit, and the DFB-LD 13 may function as a light source.

[0049] Transmission signal data 5 input from the outside is received by the EAM driving circuit 24, and output to the EAM 23 via an EAM signal line, and a burst control signal 6 is received by the burst-mode LD driving circuit 31 and the pre-emphasis circuit 35, and output to the DFB-LD 13 via a LD bias line 25. In addition, illustration is given while focusing attention only on a transmission unit of the transceiver 1 equipped in an GNU (receiver unit and other peripheral circuits are omitted).

[0050] In addition, FIG. 7 illustrates a burst control circuit in the present embodiment. The burst control circuit includes the DFB-LD 13, a bypass capacitor 14, the burst-mode LD driving circuit 31, the pre-emphasis circuit 35, an electrode #1-54, an electrode #2-55, and a ground electrode 56. As illustrated in FIG. 4, the bypass capacitor 14 has a function of removing a noise component entering bias current (Ib) 61. In FIG. 7 the bypass capacitor 14 functions as a capacitor included in a light source.

[0051] FIG. 8 illustrates a time chart in the present embodiment. In FIG. 6, the transmission unit mainly includes the EML-TOSA 22 including the EML (the DFB-LD 13 and the EAM 23), the burst-mode LD driving circuit 31, the pre-emphasis circuit 35, and the EAM driving circuit 24.

[0052] Burst signal light 10 transmitted from the transceiver 1 is generated in the following manner. The transmission signal data 5 having a signal speed of the 10 Gb/s level that has been transmitted from a higher layer (not illustrated) of the transceiver 1 includes idle signals 52 and data signals 51, and the data signals 51 are upstream signals to be transmitted by the transceiver 1 for the GNU, toward an OLT, and the transmission timing of the data signals 51 is controlled by the On/Off control of the burst control signal 6 (refer to FIG. 8). Here, the burst control signal 6 is input to the burst-mode LD driving circuit 31 and the pre-emphasis circuit 35.

[0053] As illustrated in FIG. 7, from the burst-mode LD driving circuit 31, according to the On/Off of the burst control signal 6, LD driver current 63 is output during On. In addition, similarly, from the pre-emphasis circuit 35, according to the On/Off of the burst control signal 6, pre-emphasis current (I.sub.pe) 64 is output during On. In addition, the pre-emphasis circuit 35 may output a pre-emphasis control signal for superimposing an additional signal for charging the capacitor, on a driving signal, as the pre-emphasis current (I.sub.pe) 64, at the vicinity of the beginning of the burst control signal 6, or at a timing earlier than the beginning.

[0054] Thus, by the pre-emphasis current (I.sub.pe) 64 being superimposed on the LD driver current (I.sub.LDD) 63, resultant current is applied as superimposed current (I.sub.LDD+pe) 65 to the DFB-LD 13 via the LD bias line 25. Output light emitted from the DFB-LD 13 is converted by the EAM 23 into a modulation signal, and transmitted by the transceiver 1 as the burst signal light 10.

[0055] Here, the pre-emphasis current (I.sub.pe) 64 output from the pre-emphasis circuit 35, which serves as the most characteristic feature of the present embodiment, is additionally applied for a time until the bypass capacitor (C.sub.bp) 14 is charged, as illustrated in FIG. 8, for supplementing a deficient amount generated by bypass capacitor current (I.sub.c) 62 flowing for the time until the bypass capacitor (C.sub.bp) 14 is charged.

[0056] Here, if a rising start time of the LD driver current 63 is denoted by t0, a rising start time of the pre-emphasis current 64 is denoted by t1, and a falling start time of the pre-emphasis current 64 is denoted by t3, in the present embodiment, t0 is set to an arbitrary value, and the values are set so that t1=t0, t3=t0 30 ps are satisfied. In other words, a time for which the pre-emphasis current flows is 30 ps. In addition, the pre-emphasis current 64 flowing when the burst control signal 6 is turned On/Off is assumed to be 30 mA/0 mA.

[0057] The time for which the pre-emphasis current 64 flows is a time until the bypass capacitor 14 is charged, and is not limited to 30 ps. The time for which the pre-emphasis current 64 flows is not limited to a time required for charging 100% of load capability C.sub.p, and an arbitrary rate can be used. For example, a first predetermined rate of the load capability C.sub.p can be an arbitrary rate being, for example, equal to or larger than 50% and equal to or smaller than 100%, and is preferably a rate being equal to or larger than 75% and equal to or smaller than 95%, in terms of the shortening of a charging time of the pre-emphasis current 64.

[0058] When forward voltage in a transitional response process of the DFB-LD 13 is denoted by V.sub.f, load capability of the bypass capacitor 14 is denoted by C.sub.p, and bypass capacitor current 62 flowing to the bypass capacitor 14 is denoted by I.sub.chg, a charging time T.sub.chg until the bypass capacitor 14 is charged can be represented by the following formula.

(Math. 1)

T.sub.chg=(V.sub.f×C.sub.p)/I.sub.chg  (1)

[0059] According to the above formula, if charging current i.sub.chg is increased, a charging time t.sub.chg becomes shorter. Thus, by increasing the charging current of the bypass capacitor 14 by injecting a pre-emphasis signal in a pulse manner, aside from the driving signal, the rising time can be speeded up.

[0060] In this manner, as illustrated in FIG. 8, a transitional response of the bias current (I.sub.b) 61 has been speeded up by the pre-emphasis current (I.sub.pe) 64 output from the pre-emphasis circuit 35, and a burst rising time of the burst signal light 10 (burst response time of the data optical signal 101) has also been improved to 50 ps.

[0061] FIGS. 10 and 11 illustrate specific evaluation results of the rising time of the burst optical signal. FIG. 10 illustrates a case in which the pre-emphasis circuit 35 does not flow the pre-emphasis current 64, and FIG. 11 illustrates a case in which the pre-emphasis circuit 35 flows the pre-emphasis current 64. The forward voltage V.sub.f in the transitional response process of the DFB-LD 13 is 0 to 2.5 V, the load capability C.sub.p of the bypass capacitor 14 is 100 pF, the bypass capacitor current I.sub.chg is 0 to 10 mA, and the pre-emphasis current 64 from the pre-emphasis circuit 35 is 20 mA. The EAM 23 has performed modulation at 10 Gbit/s.

[0062] While a burst optical signal rising time illustrated in FIG. 10 is 60 ns, a burst optical signal rising time illustrated in FIG. 11 is 15 ns. In this manner, by flowing the pre-emphasis current 64, an effect of improving the burst rising time by 75% can be confirmed.

[0063] In addition, in the present embodiment, a modulation speed with the 10 G/bs level is used, but in the control method in the present embodiment, a modulation speed other than 10 Gb/s (for example, 1 Gb/s, 25 Gb/s, 40 Gb/s, equal to or larger than 40 Gb/s, or the like) can be applied to the modulation speed. In addition, in the present embodiment, an EML-type external modulation integrated-type light source is used, but it is apparent that a similar effect is obtained by using an external modulation integrated-type light source having a configuration in which a semiconductor Mach-Zehnder modulator (MZM) and the DFB-LD 13 are integrated.

[0064] In addition, the light source is not limited to the DFB-LD 13, and it is apparent that a similar effect is obtained by using a wavelength-tunable laser. Furthermore, it is apparent that the present invention can also be applied to an external modulator type light source having a configuration in which the BAN 23 or an MZM-type external modulator module (semiconductor MZM or LN modulator), and a DFB-LD module are separate modules, and these modules are connected by an optical connection means such as an optical fiber.

[0065] Based on the foregoing, the DFB-LD 13 functioning as a light source may include a parasitic capacitor underlying in the DFB-LD 13 in the process of manufacturing of the DFB-LD 13, as illustrated in FIGS. 12 and 13. The light source may be a distributed feedback-semiconductor laser, a distribution Bragg reflector-semiconductor laser, or a wavelength-variable laser. In addition, according to the present invention, in some cases, the bypass capacitor 14 is implemented in a light source (FIG. 7). Alternatively, in some cases, there is a parasitic capacitor 15 underlying in the light source (FIG. 12). Alternatively, in some cases, there is the parasitic capacitor 15 underlying in the light source, and the bypass capacitor 14 is implemented (FIG. 13). According to the present invention, in these cases, by applying pre-emphasis current at the same timing as a burst control signal, or at a timing earlier than the burst control signal, the rising of the burst optical signal can be improved.

[0066] FIG. 12 illustrates an equivalent circuit in a case in which a parasitic capacitor is included in the DFB-LD 13. In the configuration illustrated in FIG. 12, instead of the bypass capacitor current (Ic) 62 flowing in the bypass capacitor 14, parasitic capacitor current 66 flows in the parasitic capacitor 15. In the case of a burst optical signal transmission device adopting the configuration illustrated in FIG. 12, in the embodiment described with reference to FIG. 7, the capacitor capacity of the parasitic capacitor 15 is read instead of the capacitor capacity of the bypass capacitor 14, and the parasitic capacitor current 66 is read instead of the bypass capacitor current (Ic) 62. The burst optical signal transmission device adopting the configuration illustrated in FIG. 12 can be thereby executed.

[0067] FIG. 13 illustrates an equivalent circuit in a case in which the bypass capacitor 14 is included, and a parasitic capacitor is further included in the DFB-LD 13. In the configuration illustrated in FIG. 13, the bypass capacitor current (Ic) 62 flows in the bypass capacitor 14, and furthermore, the parasitic capacitor current 66 flows in the parasitic capacitor 15. In the case of a burst optical signal transmission device adopting the configuration illustrated in FIG. 13, in the embodiment described with reference to FIG. 7, the combined value of capacitor capacities of the bypass capacitor 14 and the parasitic capacitor 15 is read instead of the capacitor capacity of the bypass capacitor 14, and the bypass capacitor current (Ic) 62 and the parasitic capacitor current 66 are read instead of the bypass capacitor current (Ic) 62. The burst optical signal transmission device adopting the configuration illustrated in FIG. 13 can be thereby executed.

[0068] In addition, the transceiver 1 according to the present embodiment may be applied not only to an ONU, but also to an OLT. In addition, the transceiver 1 can be used in a transmission device for arbitrary optical packet switching (OPS) that transmits a burst optical signal, and the like.

Second Embodiment of Invention

[0069] A control method for a 10 Gb/s level external modulator type burst optical signal transmitter being a second embodiment of the present invention will be described in detail below based on FIGS. 6 to 7, and 9. FIG. 6 illustrates a configuration of the 10 Gb/s level external modulator type burst signal optical transmitter being the second embodiment of the present invention, and illustration is given while focusing attention only on a transmission unit of a transceiver 1 equipped in an GNU (receiver unit and other peripheral circuits are omitted).

[0070] In addition, FIG. 7 illustrates a burst control circuit in the present embodiment, and FIG. 9 illustrates a time chart in the present embodiment. In FIG. 6, the transmission unit mainly includes the EML-TOSA 22 including the EML (the DFB-LD 13 and the EAM 23), the burst-mode LD driving circuit 31, the pre-emphasis circuit 35, and the EAM driving circuit 24.

[0071] Burst signal light 10 transmitted from the transceiver 1 is generated in the following manner. Transmission signal data 5 having a signal speed of the 10 Gb/s level that has been transmitted from a higher layer (not illustrated) of the transceiver 1 includes idle signals 52 and data signals 51, and the data signals 51 are upstream signals to be transmitted by the transceiver 1 for the ONU, toward an OLT, and the transmission timing of the data signals 51 is controlled by the On/Off control of the burst control signal 6 (refer to FIG. 9). Here, the burst control signal 6 is input to the burst-mode LD driving circuit 31 and the pre-emphasis circuit 35.

[0072] As illustrated in FIG. 7, from the burst-mode LD driving circuit 31, according to the On/Off of the burst control signal 6, LD driver current (I.sub.LDD) 63 is output during On. In addition, similarly, from the pre-emphasis circuit 35, according to the On/Off of the burst control signal 6, pre-emphasis current (I.sub.pe) 64 is output during On.

[0073] Thus, by the pre-emphasis current (I.sub.pe) 64 being superimposed on the LD driver current (I.sub.LDD) 63, resultant current is applied as superimposed current (I.sub.LDD+pe) 65 to the DFB-LD 13 via the LD bias line 25. Output light emitted from the DFB-LD 13 is converted by the EAM 23 into a modulation signal, and transmitted by the transceiver 1 as the burst signal light.

[0074] Here, the pre-emphasis current (I.sub.pe) 64 output from the pre-emphasis circuit 35, which serves as a characteristic feature of the present embodiment, is additionally applied for a time until the bypass capacitor (C.sub.bp) 14 is charged, as illustrated in FIG. 9, for supplementing a deficient amount generated by bypass capacitor current (I.sub.c) 62 flowing for the time until the bypass capacitor (C.sub.bp) 14 is charged.

[0075] Here, if a rising start time of the LD driver current 63 is denoted by t0, a rising start time of the pre-emphasis current 64 is denoted by t1, and a falling start time of the pre-emphasis current 64 is denoted by t3, in the present embodiment, t0 is set to an arbitrary value, and the values are set so that t1=t0−15 ps, t3=t0+15 ps are satisfied. In other words, the time for which the pre-emphasis current (I.sub.pe) 64 flows is 30 ps, which is similar to the first embodiment, and the most characteristic feature of the present embodiment lies in that the rising start time t1 of the pre-emphasis current 64 is set to be earlier than the rising start time t0 of the LD driver current 63 (t1<t0). By providing an offset time between the t0 and the t1 in this manner, a burst response of the bias current (Ib) 61 has been significantly improved, and a burst rising time of the burst signal light 10 (burst response time of the data optical signal 101) has been improved to 20 ps.

[0076] The offset time provided for the pre-emphasis current 64 is a predetermined timing earlier than the beginning of the driving signal, and is not limited to 15 ps. For example, the charging time T.sub.chg of the bypass capacitor 14 can be represented by Formula (1). Thus, the predetermined timing is defined based on the load capability C.sub.p of the bypass capacitor 14, the charging current I.sub.chg to the bypass capacitor 14, and the forward voltage V.sub.f of the DFB-LD 13. The time for which the pre-emphasis current 64 flows is not limited to a time required for charging 100% of load capability C.sub.p, and an arbitrary rate can be used.

Third Embodiment of Invention

[0077] A burst optical signal transmission device according to the present embodiment further includes a current supplying unit (not illustrated) for further shortening a charging time t.sub.chg. The current supplying unit (not illustrated) may be included in a burst-mode LD driving circuit 31 or a pre-emphasis circuit 35.

[0078] The current supplying unit (not illustrated) supplies, to a DFB-LD 13, such arbitrary current as to fall within a range being smaller than a second predetermined rate being lower than the first predetermined rate of the load capability C.sub.p that has been described in the first embodiment of the present invention. For example, the second predetermined rate of the load capability C.sub.p is an arbitrary rate being, for example, equal to or larger than 0% and smaller than 50%.

[0079] The current to be supplied by the current supplying unit (not illustrated) is preferably current with such an extent that the DFB-LD 13 does not emit light. Thus, the second predetermined rate is preferably smaller than the rate of the load capability C.sub.p charged in the bypass capacitor 14 when threshold current of the DFB-LD 13 is supplied to the DFB-LD 13.

[0080] In addition, in the present embodiment, a modulation speed with the 10 G/bs level is used, but in the control method in the present embodiment, a modulation speed other than 10 Gb/s (for example, 1 Gb/s, 25 Gb/s, 40 Gb/s, equal to or larger than 40 Gb/s, or the like) can be applied to the modulation speed. In addition, in the present embodiment, an EML-type external modulation integrated-type light source is used, but it is apparent that a similar effect is obtained by using an external modulation integrated-type light source having a configuration in which a semiconductor Mach-Zehnder modulator (MZM) and the DFB-LD 13 are integrated.

[0081] In addition, the light source is not limited to the DFB-LD 13, and it is apparent that a similar effect is obtained by using a wavelength-variable laser. Furthermore, it is apparent that the present invention can also be applied to an external modulator type light source having a configuration in which the ETON 23 or an MZM-type external modulator module (semiconductor MZM or LN modulator), and a DFB-LD module are separate modules, and these modules are connected by an optical connection means such as an optical fiber. Based on the foregoing, the light source may include an external modulator, and the external modulator may be an electro absorption semiconductor modulator, a semiconductor Mach-Zehnder modulator, or a lithium niobate modulator.

[0082] As the light source, the present invention can be applied to an arbitrary light source such as a solid-state laser, in addition to a DFB laser and a surface-emitting laser.

[0083] As described above, by using the technique of the present invention, an external modulator type burst optical signal transmission device with a fast burst rising time that can perform, even in the C-band, long-distance transmission of 20 km or more that has less distortion of an optical signal waveform caused by wavelength dispersion, and does not cause a transmission error even at a burst signal transmission start, and a control method for the same can be realized.

[0084] In addition, the value of the pre-emphasis current (Ipe) 64 is an arbitrary value. In addition, in the present embodiment, a light source using a current signal as a driving signal has been described, but the present invention can also be applied to a light source using a voltage signal as a driving signal. In this case, pre-emphasis voltage is used instead of pre-emphasis current.

INDUSTRIAL APPLICABILITY

[0085] The present invention can be applied to a communication information business.

REFERENCE SIGNS LIST

[0086] 1: transceiver [0087] 5: transmission signal data [0088] 6: burst control signal [0089] 10: burst signal light [0090] 13: DFB-LD [0091] 14: bypass capacitor (Cbp) [0092] 15: parasitic capacitor [0093] 22: EML-TOSA [0094] 23: EAM [0095] 24: EAM driving circuit [0096] 25: LD bias line [0097] 27: EAM signal line [0098] 31: burst-mode LD driving circuit [0099] 35: pre-emphasis circuit [0100] 37: electrode [0101] 38: ground electrode [0102] 51: data signal [0103] 52: idle signal [0104] 54: electrode #1 [0105] 55: electrode #2 [0106] 56: ground electrode [0107] 61: bias current (Ib) [0108] 62: bypass capacitor current (I.sub.c) [0109] 63: LD driver current (I.sub.LDD) [0110] 64, 66: pre-emphasis current (I.sub.pe) [0111] 65: superimposed current (I.sub.LDD+pe) [0112] 72: EAM bias voltage (V.sub.b) [0113] 73: EAM modulation voltage amplitude (V.sub.pp) [0114] 74: pre-emphasis current control signal [0115] 101: data optical signal