WO2010090050A1 - 光通信システム及び光通信方法 - Google Patents
光通信システム及び光通信方法 Download PDFInfo
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- WO2010090050A1 WO2010090050A1 PCT/JP2010/050136 JP2010050136W WO2010090050A1 WO 2010090050 A1 WO2010090050 A1 WO 2010090050A1 JP 2010050136 W JP2010050136 W JP 2010050136W WO 2010090050 A1 WO2010090050 A1 WO 2010090050A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
- H04B10/25133—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion including a lumped electrical or optical dispersion compensator
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B2210/00—Indexing scheme relating to optical transmission systems
- H04B2210/25—Distortion or dispersion compensation
- H04B2210/252—Distortion or dispersion compensation after the transmission line, i.e. post-compensation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B2210/00—Indexing scheme relating to optical transmission systems
- H04B2210/25—Distortion or dispersion compensation
- H04B2210/254—Distortion or dispersion compensation before the transmission line, i.e. pre-compensation
Definitions
- the present invention relates to an optical communication system and an optical communication method for compensating for the amount of chromatic dispersion that occurs in a transmission line.
- Chromatic dispersion is a property that the group delay of light differs depending on the wavelength, and has a value of 16 to 17 ps / nm / km in a single mode fiber of 1.5 micron band.
- This wavelength dispersion spreads the optical transmission pulse, making it difficult to transmit optical signals over long distances.
- an optical signal can be transmitted only up to a distance of about 50 to 80 km. Since the transmission distance is shortened in inverse proportion to the square of the bit rate due to chromatic dispersion, the transmission distance of the optical signal when there is chromatic dispersion is 1 km or less at a higher bit rate, for example, 100 Gbps.
- a dispersion compensating device such as a dispersion compensating fiber is used in the current optical communication system.
- the dispersion compensation device has a dispersion compensation amount that is almost equal in absolute value and opposite in sign to the dispersion amount of chromatic dispersion that occurs in the transmission line.
- the transfer function of the dispersion compensation device is an inverse function of the transfer function of the transmission line.
- the dispersion amount of chromatic dispersion is simply referred to as the dispersion amount.
- the amount of dispersion generated in the transmission line is the dispersion compensation amount provided by the dispersion compensation device. Compensated. As a result, the waveform of the optical signal is restored at the output of the dispersion compensation device. This realizes long-distance transmission of an optical signal with a high bit rate even on a transmission path in which chromatic dispersion occurs.
- the route is switched by an optical switch or the like.
- the amount of dispersion also changes as the path is switched.
- a VIPA Virtually-Imaged Phase Phase
- a signal of 10 Gbps is as short as about several tens of kilometers, and cannot cope with switching of a route accompanied by a large change in distance.
- Non-Patent Document 1 discloses a technique for compensating for the amount of chromatic dispersion by processing an electrical signal in a device on the optical signal transmission side.
- the process in which waveform distortion is caused by chromatic dispersion is a linear process. Therefore, the dispersion compensation device that compensates for the amount of dispersion generated in the transmission path may be before or after the transmission path.
- a dispersion compensation device is provided in an apparatus on the transmission side of an optical signal before a transmission path.
- An example of a dispersion compensation device is a transversal filter configured as shown in FIG.
- the transversal filter 10 shown in FIG. 1 includes a plurality of delay elements 11, a plurality of multipliers 12, and an adder 13.
- Non-Patent Document 1 the amount of dispersion of an electrical signal input to a device on the optical signal transmission side is compensated by, for example, a transversal filter shown in FIG.
- a transversal filter shown in FIG. 1 an operation in which the dispersion amount is compensated by the transversal filter shown in FIG. 1 will be described.
- the electrical signal 20 input to the device on the fluorescent signal transmission side is given different delays by a plurality of delay elements 11 as shown in FIG.
- the output signal from each delay element 11 is input to the delay element 11 and the multiplier 12 in the next stage.
- the signal input to the multiplier 12 is referred to as a branch signal.
- the signal input to the delay element 11 in the next stage is further delayed by the delay element 11.
- the branch signal input to the multiplier 12 is multiplied by the tap coefficient output from the circuit coefficient control device 14.
- the signal multiplied by the tap coefficient by each multiplier 12 is input to the adder 13, and the sum is obtained by the adder 13.
- a value of half the symbol time of a signal to be transmitted is used as the delay interval of the delay given by each delay element 11.
- the tap coefficient supplied from the circuit coefficient control device 14 is a value obtained by the impulse response of the transfer function. Since the transfer function by chromatic dispersion is a complex function, this tap coefficient is a complex number. Therefore, the output after compensating for the dispersion amount also becomes a complex signal.
- an IQ converter built in the transmission side device applies the real part of the complex signal 21 to the in-phase component (cos component) of the optical signal, and the imaginary part of the complex signal to the quadrature component (sin component) of the optical signal. ).
- An IQ modulator is a device that divides an input signal into an in-phase (I) signal and a quadrature (Q) signal.
- Non-Patent Document 1 the technique disclosed in Non-Patent Document 1 described above can be applied to a device on the optical signal receiving side.
- complex signal information is lost by square detection when an optical signal is converted into an electric signal by a photodiode.
- Non-Patent Document 2 by performing coherent light reception and adopting a phase diversity reception configuration, information on the in-phase component (cos component) of the electric field of the received optical signal and a quadrature component ( sin component) information is extracted.
- a complex electric field signal of an optical electric field of the received optical signal is obtained, and the dispersion amount can be compensated by processing the complex electric field signal with a transversal filter.
- the ability to compensate for the dispersion amount is almost the same between the case where it is performed on the transmission side and the case where it is performed on the reception side within a range where deterioration due to the nonlinear effect of the system can be ignored.
- the waveform distortion caused by the change in the amount of dispersion can be detected only on the receiving side. Waveform distortion cannot be detected on the side.
- the amount of dispersion is compensated on the receiving side, since the waveform distortion state can always be confirmed on the receiving side, the receiving state can be quickly optimized by adaptive equalization.
- the number of delay elements required to compensate for the same dispersion amount and the branch signal output from the delay element are increased.
- the number (hereinafter referred to as the number of taps) increases significantly. For this reason, the scale of the circuit for compensating the dispersion amount becomes very large.
- Non-Patent Document 3 As a method for avoiding an extremely large circuit for compensating the dispersion amount, there is a method in which dispersion amount compensation is performed separately for the transmission side and the reception side. A technique for this is disclosed in Non-Patent Document 3, for example.
- Non-Patent Document 3 discloses a system that compensates for dispersion in an optical transmitter and an optical receiver by using an optical fiber. Dispersion compensation fibers in each of the optical transmitter and the optical receiver are arranged to reduce the amount of dispersion compensation in each of the optical transmitter and the optical receiver. This avoids an increase in the scale of the circuit that compensates for the dispersion amount.
- Non-Patent Document 3 since the optical transmitter does not know the dispersion compensation amount in the optical receiver, the dispersion compensation amount in the optical transmitter cannot be changed according to the change in the dispersion amount. .
- An object of the present invention is to provide an optical communication system and an optical communication method that solve the above-described problems.
- the present invention provides: An optical communication system in which an optical transmitter that modulates an electrical signal into an optical signal and transmits the optical transmitter and an optical receiver that receives the optical signal are connected by a first transmission line, The optical transmitter and the optical receiver compensate for the dispersion amount by the optical transmitter when there is almost no change in the dispersion amount of chromatic dispersion caused by the optical signal passing through the first transmission path. And reducing the absolute value of the reception-side dispersion compensation amount while keeping the total value of the transmission-side dispersion compensation amount for receiving and the reception-side dispersion compensation amount for compensating the dispersion amount by the optical receiver substantially constant .
- optical communication in an optical communication system in which an optical transmitter that modulates an electrical signal into an optical signal and transmits the optical transmitter and an optical receiver that receives the optical signal is connected by a first transmission path and a second transmission path.
- a method When there is almost no change in the amount of dispersion of chromatic dispersion caused by the optical signal passing through the first transmission path, a transmission-side dispersion compensation amount for compensating the dispersion amount by the optical transmitter;
- the receiver has a process of reducing the absolute value of the reception-side dispersion compensation amount while keeping the total value with the reception-side dispersion compensation amount for compensating the dispersion amount substantially constant.
- a transmission-side dispersion compensation amount for compensating the dispersion amount by the optical transmitter, and the optical receiver When there is almost no change in the amount of dispersion of chromatic dispersion caused by the optical signal passing through the transmission line, a transmission-side dispersion compensation amount for compensating the dispersion amount by the optical transmitter, and the optical receiver
- the absolute value of the reception-side dispersion compensation amount is reduced while keeping the total value with the reception-side dispersion compensation amount for compensating the dispersion amount substantially constant.
- the range in which the reception-side dispersion compensation amount can be changed is ensured to the maximum. Therefore, it is possible to avoid that the size of the network that can optimize the dispersion compensation amount is limited by the range of the dispersion compensation amount that can be compensated by the optical receiver without increasing the scale of the circuit that compensates the dispersion amount.
- FIG. 3 is a time chart showing a change in the amount of dispersion of chromatic dispersion that occurs in a transmission line by switching the path of the transmission line shown in FIG. 2.
- FIG. 4 is a time chart showing changes in dispersion compensation amounts in the transmission filter unit and the reception filter unit shown in FIG. 2 corresponding to changes in the dispersion amount shown in FIG. 3.
- 3 is a flowchart for explaining an operation for compensating for the amount of dispersion in the optical communication system shown in FIG. 2.
- FIG. 2 is a block diagram showing the configuration of the first embodiment of the optical communication system of the present invention.
- the optical communication system includes an optical transmitter 101 and an optical receiver 108, and the optical transmitter 101 and the optical receiver 108 transmit a first data signal.
- a transmission line 107 which is a transmission line
- a control signal transmission line 112 which is a second transmission line.
- the fluorescent transmitter 101 includes a signal source 102, a circuit coefficient control unit 103 which is a first circuit coefficient control unit, a transmission filter unit 104, a light source 105, and an optical modulation unit 106.
- the saddle signal source 102 outputs a digital data signal that is an electrical signal.
- bit rate of the digital data signal is 10 Gbps, this is an example, and the present invention is not limited to this bit rate.
- Transmission filter unit 104 is a transversal filter as shown in FIG.
- the transmission filter unit 104 linearly processes the digital data signal output from the signal source 102 by a transfer function controlled by the circuit coefficient control unit 103. Then, a signal corresponding to a variable dispersion compensation amount of ⁇ 10000 ps / nm to +10000 ps / nm is added to the digital data signal and output as a transmission signal.
- the delay interval by the delay elements (see FIG. 1) constituting the transversal filter is 50 ps, which is half of 100 ps, which is the data symbol time. This delay interval of 50 ps is an example, and can take any value other than a natural fraction of the symbol time.
- the dispersion compensation amount provided by the transmission filter unit 104 is referred to as a transmission-side dispersion compensation amount.
- the circuit coefficient control unit 103 controls a transfer function used when the transmission filter unit 104 performs linear processing on the digital data signal output from the signal source 102. Specifically, the control means that the transversal filter that constitutes the transmission filter unit 104 sets and outputs a tap coefficient that multiplies the branch signal of the signal output from each delay element (see FIG. 1). It is to be.
- the predetermined dispersion amount is compensated by setting the tap coefficient to a value corresponding to the predetermined dispersion amount to be compensated. By changing the tap coefficient, the transmission side dispersion compensation amount can be changed.
- circuit coefficient control unit 103 receives a first start instruction for starting the change of the transmission side dispersion compensation amount from the optical receiver 108 via the control signal transmission path 112, the first start instruction is received.
- the transmission side dispersion compensation amount is changed in the direction shown.
- the light source 105 outputs light having a constant intensity by a DFB (DistributedrFeedBack) laser.
- the light output from the light source 105 is not limited to the DFB laser as long as it has a quality necessary for optical communication.
- the fluorescent light modulator 106 is an IQ modulator, and divides the optical signal output from the light source 105 into an in-phase component and a quadrature component. Then, the in-phase component information included in the transmission signal output from the transmission filter unit 104 is applied to the divided in-phase component, and the quadrature component information included in the transmission signal output from the transmission filter unit 104 is divided. Apply to orthogonal component. Then, the optical signal to which the information of the in-phase component and the quadrature component is applied is transmitted to the optical receiver 108 via the transmission path 107.
- the light modulation unit 106 is a modulator called an IQ modulator (or vector modulator).
- the IQ modulator is a general modulator that is widely used in a four-phase phase shift keying (QPSK) modulation method and the like, and thus detailed description thereof is omitted here.
- the optical receiver 108 shown in FIG. 2 includes a circuit coefficient control unit 109, which is a second circuit coefficient control unit, a receiving unit 110, and a reception filter unit 111.
- Receiving section 110 receives an optical signal transmitted from optical transmitter 101 via transmission path 107 using a coherent light receiving method, and detects an in-phase component signal and a quadrature component signal. Then, the detected in-phase component signal and quadrature component signal are output to the reception filter unit 111 as reception signals.
- Reception filter unit 111 is a transversal filter as shown in FIG.
- the reception filter unit 111 linearly processes the reception signal output from the reception unit 110 by a transfer function controlled by the circuit coefficient control unit 109. Then, a signal corresponding to a variable dispersion compensation amount of ⁇ 10000 ps / nm to +10000 ps / nm is added to the received signal and output.
- the delay interval by the delay elements (see FIG. 1) constituting the transversal filter is 50 ps, which is half of the data symbol time of 100 ps. This delay interval of 50 ps is an example, and can take any value other than a natural fraction of the symbol time.
- the reception filter unit 111 detects the amount of dispersion of the reception signal output from the reception unit 110, and performs adaptive equalization so that the amount of dispersion is minimized according to an instruction from the circuit coefficient control unit 109.
- the dispersion compensation amount provided by the reception filter unit 111 is referred to as a reception-side dispersion compensation amount.
- the circuit coefficient control unit 109 controls the transfer function used when the reception filter unit 111 performs linear processing on the reception signal output from the reception unit 110, as with the circuit coefficient control unit 103. Specifically, the control means that the transversal filter that constitutes the reception filter unit 111 sets and outputs a tap coefficient that multiplies the branch signal of the signal output from each delay element (see FIG. 1). It is to be.
- the predetermined dispersion amount is compensated by setting the tap coefficient to a value corresponding to the predetermined dispersion amount to be compensated. By changing the tap coefficient, the reception-side dispersion compensation amount can be changed.
- the circuit coefficient control unit 109 monitors the amount of dispersion detected by the reception filter unit 111.
- the circuit coefficient control unit 109 minimizes the amount of change in the dispersion amount. Adaptive equalization. Further, the circuit coefficient control unit 109 transmits a first start instruction to the circuit coefficient control unit 103 via the control signal transmission path 112.
- FIG. 3 is a time chart showing changes in the amount of dispersion of chromatic dispersion that occurs in the transmission path 107 by switching the path of the transmission path 107 shown in FIG.
- FIG. 4 is a time chart showing changes in dispersion compensation amounts in the transmission filter unit 104 and the reception filter unit 111 shown in FIG. 2 corresponding to changes in the dispersion amount shown in FIG. 3, and (a) is a reception filter unit.
- 111 is a time chart showing a change in the reception-side dispersion compensation amount at 111
- (b) is a time chart showing a change in the transmission-side dispersion compensation amount in the transmission filter unit 104
- (c) is a transmission-side dispersion compensation amount and a reception-side dispersion compensation amount. It is a time chart which shows the change of the total value of.
- FIG. 5 is a flowchart for explaining the operation of compensating for the dispersion amount in the optical communication system shown in FIG.
- step S1 switching of the path is generated at time t 1 shown in FIGS. 3 and 4 (step S1).
- the amount of dispersion generated in the transmission line 107 shown in FIG. 2 increases to 10,000 ps / nm.
- Circuit coefficient control unit 109 when detecting the change in the dispersion amount, causes reception filter unit 111 to start adaptive equalization for minimizing the change amount of the dispersion amount (step S2).
- the circuit coefficient control unit 109 completes the adaptive equalization in the reception filter unit 111 when the reception side dispersion compensation amount becomes ⁇ 10000 ps / nm as shown in FIG. 4A (step S3).
- the total value of the transmission side dispersion compensation amount and the reception side dispersion compensation amount becomes stable at ⁇ 10000 ps / nm.
- the circuit coefficient control unit 109 for reducing the transmission side dispersion compensation amount (increasing the absolute value with a negative dispersion compensation amount)
- a first start instruction is transmitted to the circuit coefficient control unit 103 via the control signal transmission path 112 (step S4).
- the circuit coefficient control unit 103 decreases the transmission side dispersion compensation amount in the transmission filter unit 104 (step S5). Thereby, as shown in FIG. 4B, the transmission side dispersion compensation amount becomes ⁇ 10000 ps.
- the circuit coefficient control unit 109 decreases the absolute value of the reception side dispersion compensation amount in the reception filter unit 111 (step S6). Specifically, as shown in FIG. 4A, the dispersion compensation amount in the reception filter unit 111 is increased to ⁇ 0 ps / nm.
- the transmission-side dispersion compensation amount and the reception-side dispersion compensation amount change while the total value of the transmission-side dispersion compensation amount and the reception-side dispersion compensation amount is kept substantially constant.
- the circuit coefficient control unit 109 changes the reception-side dispersion compensation amount in the reception filter unit 111 according to the dispersion amount detected by the reception filter unit 111.
- the circuit coefficient control unit 109 determines whether or not the absolute value of the reception side dispersion compensation amount is minimized (step S7).
- step S7 when the absolute value of the reception side dispersion compensation amount is not the minimum, the operation proceeds to step S5, and the circuit coefficient control unit 103 causes the transmission filter unit 104 to reduce the transmission side dispersion compensation amount.
- the circuit coefficient control unit 109 causes the reception filter unit 111 to continue increasing the reception side dispersion compensation amount.
- the circuit coefficient control unit 109 controls a stop instruction for stopping changing the transmission side dispersion compensation amount.
- the signal is transmitted to the circuit coefficient control unit 103 via the signal transmission path 112 (step S8).
- the circuit coefficient control unit 103 When receiving the stop instruction transmitted from the circuit coefficient control unit 109, the circuit coefficient control unit 103 stops the decrease of the transmission side dispersion compensation amount in the transmission filter unit 104 (step S9).
- the circuit coefficient control unit 109 stops increasing the reception side dispersion compensation amount in the reception filter unit 111 (step S10).
- the dispersion amount of the transmission line 107 shown in FIG. 2 is increased to 20000ps / nm.
- the circuit coefficient control unit 109 adaptively equalizes the reception filter unit 111 and changes the reception-side dispersion compensation amount to ⁇ 10000 ps / nm as shown in FIG. As a result, the communication state becomes normal.
- the circuit coefficient control unit 109 transmits a first start instruction to the circuit coefficient control unit 103 so as to decrease the transmission side dispersion compensation amount in order to reduce the absolute value of the reception side dispersion compensation amount. Since the transmission filter unit 104 cannot further reduce the transmission side dispersion compensation amount, the transmission side dispersion compensation amount does not change. As a result, as shown in FIGS. 4A and 4B, the transmission side dispersion compensation amount and the reception side dispersion compensation amount are equal and stable at ⁇ 10000 ps / nm.
- the transmission side dispersion compensation amount in the transmission filter unit 104 is already ⁇ 10000 ps / nm. Therefore, the reception filter unit 111 sets the reception side dispersion compensation amount to +10000 ps / nm by adaptive equalization as shown in FIG. As a result, the communication state becomes normal.
- the circuit coefficient control unit 109 transmits a first start instruction to the circuit coefficient control unit 103 so as to increase the transmission side dispersion compensation amount in order to decrease the absolute value of the reception side dispersion compensation amount.
- the circuit coefficient control unit 103 that has received the first start instruction transmitted from the circuit coefficient control unit 109 increases the transmission-side dispersion compensation amount to ⁇ 0 ps / nm, as shown in FIG. At this time, the circuit coefficient control unit 109 decreases the absolute value of the reception-side dispersion compensation amount. Specifically, as shown in FIG. 4A, the dispersion compensation amount of the reception filter unit 111 is reduced to ⁇ 0 ps / nm. At this time, the transmission side dispersion compensation amount and the reception side dispersion compensation amount change while the total value of the transmission side dispersion compensation amount and the reception side dispersion compensation amount is kept substantially constant.
- the transmission-side dispersion compensation amount for compensating the dispersion amount by the optical transmitter 101 The absolute value of the reception-side dispersion compensation amount is reduced while keeping the total value of the reception-side dispersion compensation amount for compensating the dispersion amount by the optical receiver 108 substantially constant.
- the range in which the reception-side dispersion compensation amount can be changed is ensured to the maximum. Therefore, it is possible to avoid that the size of the network that can optimize the dispersion compensation amount is limited by the range of the dispersion compensation amount that can be compensated by the optical receiver 108 without increasing the scale of the circuit that compensates the dispersion amount. .
- the range of dispersion compensation amount is limited to ⁇ 10000 ps / nm to +10000 ps / nm which is the range of dispersion compensation amount on the receiving side.
- the dispersion of the path is increased 20000ps / nm.
- the dispersion compensation amount on the transmission side is ⁇ 0 ps / nm, an attempt is made to reduce chromatic dispersion by adaptive equalization on the reception side.
- the dispersion compensation amount on the reception side is already the limit value of ⁇ 10000 ps / nm. Since it is nm, the dispersion compensation amount cannot be increased.
- the entire optical communication system falls within the range of ⁇ 10000 to +10000 ps / nm which is the dispersion compensation amount that can be compensated on the reception side.
- the amount of dispersion compensation is limited.
- adaptive equalization in the optical receiver 108 is used to change the reception-side dispersion compensation amount in response to the change in dispersion amount due to the switching of the transmission path 107.
- the configuration of the optical communication system can be simplified.
- the dispersion amount of the transmission path 107 has already changed, and the communication quality is likely to deteriorate with respect to fluctuations in other deterioration factors such as polarization dispersion fluctuations.
- a control start frame for instructing a change in the reception side dispersion compensation amount is embedded in the transmission signal and transmitted to the optical receiver.
- a change in the dispersion amount of the transmission path 107 is dealt with.
- FIG. 6 is a block diagram showing the configuration of the second embodiment of the optical communication system of the present invention.
- the optical communication system of this embodiment is provided with a control start frame insertion unit 207 in the optical transmitter 201 as compared with the optical communication system of the first embodiment shown in FIG. The difference is that 208 includes a control start frame detection unit 212.
- the control start frame insertion unit 207 inserts a control start frame into the digital data signal output from the signal source 202 when the circuit coefficient control unit 203 changes the transmission side dispersion compensation amount. Then, a digital data signal in which the control start frame is inserted and insertion information indicating that the control start frame has been inserted are output.
- Circuit coefficient control unit 203 changes the transmission-side dispersion compensation amount in transmission filter unit 204 when a predetermined time has elapsed since the insertion information output from control start frame insertion unit 207 was received.
- control start frame detection unit 212 When the control start frame detection unit 212 detects the control start frame in the reception signal output from the reception filter unit 211, the control start frame detection unit 212 outputs detection information for notifying that the control start frame has been detected to the circuit coefficient control unit 209. To do.
- Circuit coefficient control unit 209 changes the reception-side dispersion compensation amount in reception filter unit 211 when a predetermined time has elapsed since the detection information output from control start frame detection unit 212 was received.
- the dispersion amount of the transmission path 107 is completely compensated by using the control start frame to change the transmission side dispersion compensation amount and the reception side dispersion compensation amount synchronously, the above-described first As described in the embodiment, an operation is performed in which the reception-side dispersion compensation amount and the transmission-side dispersion compensation amount are changed synchronously so that the absolute value of the reception-side dispersion compensation amount decreases.
- the optical transmitter 201 transmits a control start frame for instructing to change the reception side dispersion compensation amount to the optical receiver 208. Therefore, the dispersion amount of the transmission path 107 can be compensated promptly and at a more accurate timing.
- the circuit coefficient control unit 203 receives the insertion information from the control start frame insertion unit 207, and changes the transmission-side dispersion compensation amount when a predetermined time elapses after the insertion information is received.
- the circuit coefficient control unit 203 instructs the control start frame insertion unit 207 to insert a control start frame, and when a predetermined time has elapsed since the instruction is given, the transmission side dispersion compensation amount is set It may be changed.
- the timing for changing the transmission-side dispersion compensation amount and the reception-side dispersion compensation amount is controlled by using the control start frame between the optical transmitter and the optical receiver.
- the control start frame since the control start frame is inserted into the transmission signal, the bit rate of the transmission path 107 changes, and there is a possibility that the existing transmission rate component cannot be used.
- the optical transmitter uses the control signal transmission path 112 to instruct the optical receiver to start changing the reception-side dispersion compensation amount.
- FIG. 7 is a block diagram showing the configuration of the third embodiment of the optical communication system of the present invention.
- the circuit coefficient control unit 303 When changing the transmission-side dispersion compensation amount, the circuit coefficient control unit 303 sends a second start instruction for instructing the start of change of the reception-side dispersion compensation amount via the control signal transmission path 112. To 309. Then, when a predetermined time has elapsed since the transmission of the second start instruction, the transmission-side dispersion compensation amount in the transmission filter unit 304 is changed.
- the circuit coefficient control unit 309 that has received the second start instruction transmitted from the circuit coefficient control unit 303 receives reception side dispersion compensation in the reception filter unit 311 when a predetermined time has elapsed after receiving the second start instruction. Change the amount.
- the dispersion amount of the transmission path 107 is compensated by using the second start instruction to change the transmission side dispersion compensation amount and the reception side dispersion compensation amount in synchronization with each other, as described above.
- an operation is performed in which the reception-side dispersion compensation amount and the transmission-side dispersion compensation amount are changed synchronously so that the absolute value of the reception-side dispersion compensation amount decreases.
- the optical transmitter 201 instructs the optical receiver 208 to change the reception-side dispersion compensation amount by using the control signal transmission path 112. Therefore, the dispersion amount of the transmission path 107 can be compensated promptly and with more accurate timing without changing the bit rate of the transmission path 107.
- the timing at which the transmission-side dispersion compensation amount in the transmission filter section 304 is changed, and the reception filter section 311 There may be a deviation from the timing of changing the reception-side dispersion compensation amount.
- signal quality degradation may be reduced by, for example, performing changes in the transmission side dispersion compensation amount and reception side dispersion compensation amount in small increments. Must be kept to a minimum.
- the change in the reception-side dispersion compensation amount in the reception filter and the change in the transmission-side dispersion compensation amount in the transmission filter are simultaneously performed.
- both the transmission filter unit and the reception filter unit need to perform filter processing on the in-phase component and the quadrature component of signals input to them, the set amount of each tap coefficient becomes enormous.
- even a small change in dispersion compensation amount due to the filter processing is accompanied by a large change in filter coefficient, it is difficult to stably change the dispersion compensation amount unless high-precision control is performed.
- the tap filter is updated by dividing the transmission filter unit and the reception filter unit into two, and dividing the dispersion compensation amount to be compensated in the transmission filter unit and the reception filter unit into two. Reduce the amount to do.
- the transversal filter that constitutes the transmission filter unit and the reception filter unit performs inverse function processing of the transfer function of the transmission path 107.
- the value of the impulse response coefficient obtained by the inverse Fourier transform of the inverse function may be multiplied as the tap coefficient value in the multiplier of the output of each delay element.
- K is a constant depending on the wavelength of the optical signal, and is approximately 62500 at the wavelength of 1500 nm.
- FIG. 8 is a diagram illustrating an example of coefficient values of real and imaginary parts of an impulse response in each tap when the bit rate is 10 Gbps and the delay interval of the transversal filter is 50 ps.
- the vertical axis indicates the coefficient values of the real part and the imaginary part of the impulse response at each tap, which are indicated as tap coefficient values in the figure.
- the coefficient value of the real part is almost 0 after the 12th tap from the center.
- the coefficient value of the real part is almost 0 after the 14th tap from the center.
- the coefficient value of the real part has a value larger than 0 even after the 20th tap from the center.
- the transmission filter unit and the reception filter unit are each divided into two, and in one transmission filter unit and the reception filter unit, 2K calculated by changing the value of n in the above equation (1). / dispersion amount of a constant multiple of B 2 the steps compensated.
- a small dispersion amount other than a dispersion amount that is a constant multiple of 2K / B 2 calculated by changing the value of n in the above equation (1) is fixed. Compensate. Thereby, the amount of updating the tap coefficient can be reduced.
- FIG. 9 is a block diagram showing the configuration of the fourth embodiment of the optical communication system of the present invention.
- the optical communication system according to the present embodiment is different from the optical communication systems according to the first to third embodiments shown in FIG. 2, FIG. 6 and FIG.
- a transmission filter unit 404-1 as a first transmission filter unit and a transmission filter unit 404-2 as a second transmission filter unit
- a circuit coefficient setting unit 407 is provided.
- the reception filter unit is divided into a reception filter unit 411-1 that is a first reception filter unit and a reception filter unit 411-2 that is a second reception filter unit, Further, the circuit coefficient setting unit 412 is provided.
- Circuit coefficient setting section 407 outputs tap coefficients used when transmission filter sections 404-1 and 404-2 perform compensation to circuit coefficient control section 403 and transmission filter section 404-2.
- the transmission filter unit 404-1 performs first transmission side dispersion for stepwise compensating for a dispersion amount that is a constant multiple of 2K / B 2 calculated by changing the value of n in the above equation (1).
- a signal corresponding to the compensation amount is added to the digital data signal output from the signal source 402. Then, the digital data signal to which the first transmission side dispersion compensation amount is added is output to the transmission filter unit 404-2 as the first transmission side compensated signal.
- the transmission filter unit 404-2 is configured to fixedly compensate for a minute dispersion amount other than a dispersion amount that is a constant multiple of 2K / B 2 calculated by changing the value of n in the above equation (1).
- a signal corresponding to the second transmission-side dispersion compensation amount is added to the first transmission-side compensated signal output from the transmission filter unit 404-1.
- the first transmission side compensated signal to which the second transmission side dispersion compensation amount is added is output to the optical modulation unit 406 as a transmission signal.
- the transmission filter unit 404-2 only compensates for a small amount of dispersion, so the circuit scale is small.
- the circuit coefficient setting unit 412 outputs the tap coefficients used when the reception filter units 411-1 and 411-2 perform compensation to the circuit coefficient control unit 409 and the reception filter unit 411-2.
- the reception filter unit 411-1 includes a first reception-side dispersion for compensating stepwise for a dispersion amount that is a constant multiple of 2K / B 2 calculated by changing the value of n in the above equation (1).
- a signal corresponding to the compensation amount is added to the reception signal output from the reception unit 410.
- the reception signal to which the first reception-side dispersion compensation amount is added is output to the reception filter unit 411-2 as the first reception-side compensated signal.
- the reception filter unit 411-2 fixedly compensates for a minute dispersion amount other than a dispersion amount that is a constant multiple of 2K / B 2 calculated by changing the value of n in the above equation (1).
- a signal corresponding to the second reception-side dispersion compensation amount is added to the first reception-side compensated signal output from the reception filter unit 411-1 and output. Since the reception filter unit 411-2 only compensates for a small amount of dispersion, the circuit scale is small.
- the transmission filter unit and the reception filter unit are each divided into two, and the transmission filter unit 404-1 and the reception filter unit 411-1 compensate for a dispersion amount that is a constant multiple of a predetermined dispersion amount.
- the transmission filter unit 404-2 and the reception filter unit 411-2 fixedly compensate for a dispersion amount other than a constant multiple of the predetermined dispersion amount. Therefore, the amount of updating the tap coefficient can be reduced.
- FIG. 10 is a diagram illustrating another example of the coefficient values of the real part and the imaginary part of the impulse response in each tap when the delay rate of the transversal filter is 50 ps with respect to the bit rate of 10 Gbps.
- N 5
- the vertical axis indicates the values of the coefficients of the real part and the imaginary part of the impulse response at each tap, which are indicated as tap coefficient values in the figure.
- the coefficient value of the imaginary part is almost 0 after the 11th tap from the center.
- the coefficient value of the imaginary part is almost 0 after the 13th tap from the center.
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Abstract
Description
電気信号を光信号に変調して送信する光送信機と、前記光信号を受信する光受信機とが第1の伝送路によって接続された光通信システムであって、
前記光送信機及び前記光受信機は、前記光信号が前記第1の伝送路を通ることによって発生する波長分散の分散量の変化がほぼ無くなると、前記光送信機によって前記分散量を補償するための送信側分散補償量と、前記光受信機によって前記分散量を補償するための受信側分散補償量との合計値をほぼ一定に保ちながら、前記受信側分散補償量の絶対値を減少させる。
前記光信号が前記第1の伝送路を通ることによって発生する波長分散の分散量の変化がほぼ無くなると、前記光送信機によって前記分散量を補償するための送信側分散補償量と、前記光受信機によって前記分散量を補償するための受信側分散補償量との合計値をほぼ一定に保ちながら、前記受信側分散補償量の絶対値を減少させる処理を有する。
図2は、本発明の光通信システムの第1の実施形態の構成を示すブロック図である。
上述した第1の実施形態では、伝送路107の経路の切り替えによる分散量の変化に対応して受信側分散補償量を変化させるために、光受信機108における適応等化を利用した。これにより、第1の実施形態では光通信システムの構成をシンプルな構成にすることができた。しかし、適応等化が開始される時点では、伝送路107の分散量が既に変化しており、偏波分散変動等の他の劣化要因の変動に対して通信品質が劣化しやすい状況となる。
上述した第2の実施形態では、光送信機と光受信機との間で制御開始フレームを利用することにより、送信側分散補償量及び受信側分散補償量を変化させるタイミングを制御した。この場合、送信信号に制御開始フレームを挿入するため、伝送路107のビットレートが変化してしまい、既存の伝送速度のコンポーネントを用いることができなくなる可能性がある。
上述した第1~第3の実施形態では、受信フィルタにおける受信側分散補償量の変化と、送信フィルタにおける送信側分散補償量の変化とを同時に行っている。この場合、送信フィルタ部と受信フィルタ部を構成するトランスバーサルフィルタのフィルタ係数を同時に変更する必要がある。しかし、送信フィルタ部及び受信フィルタ部のいずれにおいても、それらに入力される信号の同相成分及び直交成分に対するフィルタ処理が必要なため、それぞれのタップ係数の設定量が膨大となる。特に、フィルタ処理による微小な分散補償量の変化に対しても、大きなフィルタ係数の変化が伴う場合、精度の高い制御を行わないと安定して分散補償量を変化させることが難しい。
Claims (18)
- 電気信号を光信号に変調して送信する光送信機と、前記光信号を受信する光受信機とが第1の伝送路によって接続された光通信システムであって、
前記光送信機及び前記光受信機は、前記光信号が前記第1の伝送路を通ることによって発生する波長分散の分散量の変化がほぼ無くなると、前記光送信機によって前記分散量を補償するための送信側分散補償量と、前記光受信機によって前記分散量を補償するための受信側分散補償量との合計値をほぼ一定に保ちながら、前記受信側分散補償量の絶対値を減少させる光通信システム。 - 請求項1に記載の光通信システムにおいて、
前記光送信機と前記光受信機との間を接続する第2の伝送路を有し、
前記光送信機は、
前記送信側分散補償量に相当する信号を前記電気信号に付与して送信信号として出力する送信フィルタ部と、
前記送信側分散補償量を変化させる第1の回路係数制御部と、
前記送信フィルタ部から出力された前記送信信号を変調して前記光信号として前記光受信機へ送信する光変調部と、を有し、
前記光受信機は、
前記光変調部から送信された前記光信号を受信し、該受信した前記光信号を電気信号に変換した受信信号を出力する受信部と、
前記受信部から出力された前記受信信号の前記分散量を検出し、該検出された前記分散量に応じ、前記受信側分散補償量に相当する信号を前記受信信号に付与して出力する受信フィルタ部と、
前記受信フィルタ部が検出する前記分散量を監視し、前記受信側分散補償量を変化させる第2の回路係数制御部と、を有し、
前記第2の回路係数制御部は、前記分散量の変化がほぼ無くなると、前記受信側分散補償量の絶対値を減少させる方向に前記送信側分散補償量を変化させるための第1の開始指示を前記第2の伝送路を介して前記第1の回路係数制御部へ送信し、前記受信側分散補償量と前記送信側分散補償量との合計値をほぼ一定に保ちながら、前記受信側分散補償量の絶対値を減少させる方向に前記受信側分散補償量を変化させ、
前記第1の回路係数制御部は、前記第2の回路係数制御部から送信された前記第1の開始指示を受信すると、該第1の開始指示が示す方向に前記送信側分散補償量を変化させる光通信システム。 - 請求項2に記載の光通信システムにおいて、
前記第2の回路係数制御部は、前記受信側分散補償量の絶対値が最小となったことを検知すると、前記送信側分散補償量を変化させるのを停止させるための停止指示を前記第2の伝送路を介して前記第1の回路係数制御部へ送信するとともに、前記受信側分散補償量を変化させるのを停止し、
前記第1の回路係数制御部は、前記第2の回路係数制御部から送信された前記停止指示を受信すると、前記送信側分散補償量を変化させるのを停止する光通信システム。 - 請求項2または請求項3に記載の光通信システムにおいて、
前記第2の回路係数制御部は、前記受信フィルタ部が検出する前記分散量の変化を検知すると、該変化の変化量が最小となるように前記受信側分散補償量を変化させる光通信システム。 - 請求項2または請求項3に記載の光通信システムにおいて、
前記光送信機は、前記送信側分散補償量の変化を開始する際、前記受信側分散補償量の変化を開始させるための制御開始フレームを前記電気信号に挿入し、該制御開始フレームを挿入した前記電気信号と、前記制御開始フレームを挿入したことを示す挿入情報を出力する制御開始フレーム挿入部を有し、
前記光受信機は、前記受信部から出力された受信信号から前記制御開始フレームを検出し、該制御開始フレームを検出したことを示す検出情報を出力する制御開始フレーム検出部を有し、
前記第1の回路係数制御部は、前記制御開始フレーム挿入部から出力された前記挿入情報を受け付けてから所定の時間が経過すると、前記送信側分散補償量を変化させ、
前記第2の回路係数制御部は、前記制御開始フレーム検出部から出力された前記検出情報を受け付けてから所定の時間が経過すると、前記受信側分散補償量を変化させる光通信システム。 - 請求項2または請求項3に記載の光通信システムにおいて、
前記光送信機は、前記受信側分散補償量の変化を開始させるための制御開始フレームを前記電気信号に挿入して出力する制御開始フレーム挿入部を有し、
前記光受信機は、前記受信部から出力された受信信号から前記制御開始フレームを検出し、該制御開始フレームを検出したことを示す検出情報を出力する制御開始フレーム検出部を有し、
前記第1の回路係数制御部は、前記送信側分散補償量の変化を開始する際、前記制御開始フレーム挿入部に対し、前記制御開始フレームを前記電気信号に挿入する指示をし、該指示をしてから所定の時間が経過すると、前記送信側分散補償量を変化させ、
前記第2の回路係数制御部は、前記制御開始フレーム検出部から出力された前記検出情報を受け付けてから所定の時間が経過すると、前記受信側分散補償量を変化させる光通信システム。 - 請求項2または請求項3に記載の光通信システムにおいて、
前記第1の回路係数制御部は、前記送信側分散補償量の変化を開始する際、前記受信側分散補償量の変化を開始させるための第2の開始指示を前記第2の伝送路を介して前記第2の回路係数制御部へ送信し、前記第2の開始指示を送信してから所定の時間が経過すると、前記送信側分散補償量を変化させ、
前記第2の回路係数制御部は、前記第1の回路係数制御部から送信された前記第2の開始指示を受信してから所定の時間が経過すると、前記受信側分散補償量を変化させる光通信システム。 - 請求項2乃至7のいずれか1項に記載の光通信システムにおいて、
前記送信フィルタ部は、
所定の分散量の定数倍の前記分散量を補償するための第1の送信側分散補償量に相当する信号を前記電気信号に付与して第1の送信側補償済信号として出力する第1の送信フィルタ部と、
前記所定の分散量の定数倍以外の前記分散量を補償するための第2の送信側分散補償量に相当する信号を前記第1の送信フィルタ部から出力された前記第1の送信側補償済信号に付与して前記送信信号として出力する第2の送信フィルタ部と、に分割され、
前記受信フィルタ部は、
所定の分散量の定数倍の前記分散量を補償するための第1の受信側分散補償量に相当する信号を前記受信信号に付与して第1の受信側補償済信号として出力する第1の受信フィルタ部と、
前記所定の分散量の定数倍以外の前記分散量を補償するための第2の受信側分散補償量に相当する信号を前記第1の受信フィルタ部から出力された前記第1の受信側補償済信号に付与して出力する第2の受信フィルタ部と、に分割された光通信システム。 - 請求項2乃至7のいずれか1項に記載の光通信システムにおいて、
前記送信フィルタ部は、
所定の値以上の前記分散量を補償するための第1の送信側分散補償量に相当する信号を前記電気信号に付与して第1の送信側補償済信号として出力する第1の送信フィルタ部と、
前記所定の値よりも小さな値の前記分散量を補償するための第2の送信側分散補償量に相当する信号を前記第1の送信フィルタ部から出力された前記第1の送信側補償済信号に付与して前記送信信号として出力する第2の送信フィルタ部と、に分割され、
前記受信フィルタ部は、
所定の値以上の前記分散量を補償するための第1の受信側分散補償量に相当する信号を前記受信信号に付与して第1の受信側補償済信号として出力する第1の受信フィルタ部と、
前記所定の値よりも小さな値の前記分散量を補償するための第2の受信側分散補償量に相当する信号を前記第1の受信フィルタ部から出力された前記第1の受信側補償済信号に付与して出力する第2の受信フィルタ部と、に分割された光通信システム。 - 電気信号を光信号に変調して送信する光送信機と、前記光信号を受信する光受信機とが第1の伝送路及び第2の伝送路によって接続された光通信システムにおける光通信方法であって、
前記光信号が前記第1の伝送路を通ることによって発生する波長分散の分散量の変化がほぼ無くなると、前記光送信機によって前記分散量を補償するための送信側分散補償量と、前記光受信機によって前記分散量を補償するための受信側分散補償量との合計値をほぼ一定に保ちながら、前記受信側分散補償量の絶対値を減少させる処理を有する光通信方法。 - 請求項10に記載の光通信方法において、
前記光送信機が、
前記送信側分散補償量に相当する信号を前記電気信号に付与して送信信号とする送信側補償処理と、
前記送信信号を変調して前記光信号として前記光受信機へ送信する処理と、
前記光受信機が、
前記光信号を受信し、該受信した前記光信号を電気信号に変換して受信信号とする処理と、
前記受信信号の前記分散量を検出する処理と、
前記検出された前記分散量に応じ、前記受信側分散補償量に相当する信号を前記受信信号に付与する受信側補償処理と、
前記分散量の変化がほぼ無くなると、前記受信側分散補償量の絶対値を減少させる方向に前記送信側分散補償量を変化させるための第1の開始指示を前記第2の伝送路を介して前記光送信機へ送信し、前記受信側分散補償量と前記送信側分散補償量との合計値をほぼ一定に保ちながら、前記受信側分散補償量の絶対値を減少させる方向に前記受信側分散補償量を変化させる処理と、
前記光送信機が、前記第1の開始指示を受信すると、該第1の開始指示が示す方向に前記送信側分散補償量を変化させる処理と、を有する光通信方法。 - 請求項11に記載の光通信方法において、
前記光受信機が、前記受信側分散補償量の絶対値が最小となったことを検知すると、前記送信側分散補償量を変化させるのを停止させるための停止指示を前記第2の伝送路を介して前記光送信機へ送信するとともに、前記受信側分散補償量を変化させるのを停止する処理と、
前記光送信機が、前記光受信機から送信された前記停止指示を受信すると、前記送信側分散補償量及を変化させるのを停止する処理と、をさらに有する光通信方法。 - 請求項11または請求項12に記載の光通信方法において、
前記光受信機が、前記分散量の変化を検知すると、該変化の変化量が最小となるように前記受信側分散補償量を変化させる処理をさらに有する光通信方法。 - 請求項11または請求項12に記載の光通信方法において、
前記光送信機が、
前記送信側分散補償量の変化を開始する際、前記受信側分散補償量の変化を開始させるための制御開始フレームを前記電気信号に挿入し、前記制御開始フレームを挿入したことを示す挿入情報を出力する処理と、
前記挿入情報を受け付けてから所定の時間が経過すると、前記送信側分散補償量を変化させる処理と、
前記光受信機が、
前記受信信号から前記制御開始フレームを検出し、該制御開始フレームを検出したことを示す検出情報を出力する処理と、
前記検出情報を受け付けてから所定の時間が経過すると、前記受信側分散補償量を変化させる処理と、をさらに有する光通信方法。 - 請求項11または請求項12に記載の光通信方法において、
前記光送信機が、
前記送信側分散補償量の変化を開始する際、前記受信側分散補償量の変化を開始させるための制御開始フレームを前記電気信号に挿入させる指示をする処理と、
前記指示に応じて前記制御開始フレームを前記電気信号へ挿入する処理と、
前記指示をしてから所定の時間が経過すると、前記送信側分散補償量の変化を開始させる処理と、
前記光受信機が、
前記受信信号から前記制御開始フレームを検出し、該制御開始フレームを検出したことを示す検出情報を出力する処理と、
前記検出情報を受け付けてから所定の時間が経過すると、前記受信側分散補償量の変化を開始させる処理と、をさらに有する光通信方法。 - 請求項11または請求項12に記載の光通信方法において、
前記光送信機が、
前記送信側分散補償量の変化を開始する際、前記受信側分散補償量の変化の開始を指示するための第2の開始指示を前記第2の伝送路を介して前記光受信機へ送信する処理と、
前記第2の開始指示を送信してから所定の時間が経過すると、前記送信側分散補償量を変化させる処理と、
前記光受信機が、前記第2の開始指示を受信してから所定の時間が経過すると、前記受信側分散補償量を変化させる処理と、をさらに有する光通信方法。 - 請求項11乃至16のいずれか1項に記載の光通信方法において、
前記送信側補償処理は、
所定の分散量の定数倍の前記分散量を補償するための第1の送信側分散補償量に相当する信号を前記電気信号に付与して第1の送信側補償済信号とする第1の送信側補償処理と、
前記所定の分散量の定数倍以外の前記分散量を補償するための第2の送信側分散補償量に相当する信号を前記第1の送信側補償済信号に付与して前記送信信号とする第2の送信側補償処理と、を含み、
前記受信側補償処理は、
所定の分散量の定数倍の前記分散量を補償するための第1の受信側分散補償量に相当する信号を前記受信信号に付与して第1の受信側補償済信号とする第1の受信側補償処理と、
前記所定の分散量の定数倍以外の前記分散量を補償するための第2の受信側分散補償量に相当する信号を前記第1の受信側補償済信号に付与する第2の受信側補償処理と、を含む光通信方法。 - 請求項11乃至16のいずれか1項に記載の光通信方法において、
前記送信側補償処理は、
所定の値以上の前記分散量を補償するための第1の送信側分散補償量に相当する信号を前記電気信号に付与して第1の送信側補償済信号とする第1の送信側補償処理と、
前記所定の値よりも小さな値の前記分散量を補償するための第2の送信側分散補償量に相当する信号を前記第1の送信側補償済信号に付与して前記送信信号とする第2の送信側補償処理と、を含み、
前記受信側補償処理は、
所定の値以上の前記分散量を補償するための第1の受信側分散補償量に相当する信号を前記受信信号に付与して第1の受信側補償済信号とする第1の受信側補償処理と、
前記所定の値よりも小さな値の前記分散量を補償するための第2の受信側分散補償量に相当する信号を前記第1の受信側補償済信号に付与する第2の受信側補償処理と、を含む光通信方法。
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