JP5321591B2 - Optical transmitter, optical receiver, and optical communication system - Google Patents

Abstract

An optical transmitter is provided with first and second Mach-Zehnder modulators which modulate optical carriers, and a phase shift section for phase-shifting an optical signal outputted from the second Mach-Zehnder modulator.  An optical signal outputted from the first Mach-Zehnder modulator and the optical signal after the phase-shift are combined.  Assuming that the bit-rate of a transmission signal is B, when the transmission signal is transmitted in a DPSK modulation scheme, the first and second Mach-Zehnder modulators are driven according to a signal the bit-rate of which is B.  On the other hand, when the transmission signal is transmitted in a DQPSK modulation scheme, the first and second Mach-Zehnder modulators are driven according to a signal the bit-rate of which is B/2.

Description

  The present invention relates to an optical transmitter, an optical receiver, and an optical communication system that transmit and receive optical signals.

  In optical communication, DPSK (Differential Phase-Shift Keying) modulation scheme and DQPSK are typical modulation schemes applied or expected to be applied to high-speed WDM (Wavelength Division Multiplexing) optical communication systems. There is a (Differential Quadrature Phase-Shift Keying) modulation method.

  As described in Non-Patent Document 1, the DPSK modulation method has high optical noise resistance, and the device configuration and control of the transmission / reception device is simpler than the DQPSK modulation method, and is suitable for downsizing and cost reduction. . The DPSK modulation method has already been adopted in a high-speed WDM optical communication system. The configuration of the DPSK modulation transmission / reception apparatus is described in Non-Patent Document 2, for example.

  On the other hand, the DQPSK modulation method is more complicated in configuration and control of the transmission / reception apparatus than the DPSK modulation method, but it is a communication method with excellent wavelength utilization efficiency, chromatic dispersion tolerance, and polarization dispersion tolerance, and these advantages are necessary. Application to next-generation optical communication systems is expected. The configuration of a DQPSK modulation transmission / reception apparatus is described in, for example, Patent Document 1 and Non-Patent Document 3.

  Next, the configuration and operation of a conventional optical transceiver using the DPSK modulation method and the DQPSK modulation method will be described with reference to FIGS.

  First, the configuration of an optical transmitter using the DPSK modulation scheme (hereinafter referred to as a DPSK optical transmitter) and an optical receiver using the DPSK modulation scheme (hereinafter referred to as a DPSK optical receiver) will be described.

  FIG. 1 is a block diagram showing a configuration of a background art DPSK optical transmitter, and FIG. 2 is a block diagram showing a configuration of a background art DPSK optical receiver. FIG. 1 and FIG. 2 show configuration examples of a background art DPSK optical transmitter and DPSK optical receiver that transmit and receive an optical signal with a bit rate B of 40 Gbps.

  As shown in FIG. 1, a background art DPSK optical transmitter 100 includes a 16: 2 multiplexer 316, a 2: 1 multiplexer 202, a laser diode 215, an LN modulator driver (LN: Lithium Niobate) 211, and an LN modulator 401. It is the composition which has.

  2, the background art DPSK optical receiver 107 includes a 1-bit delay interferometer 441, a balanced optical-electrical signal converter 442, a 1: 2 demultiplexer 247, and a 2:16 demultiplexer 248. It is the composition which has.

  The 1-bit delay interferometer 441 includes a first arm 443, a second arm 444, an optical transmission line 445, a phase shift unit 446, and a directional coupler 447. The optical transmission line 445 is provided in the first arm 443, and the phase shift unit 446 is provided in the second arm 444.

  The optical transmission line 445 delays the optical signal transmitted by the first arm 443 by a time T = τ = 1 / B = 25 ps (picosecond) with respect to the optical signal transmitted by the second arm 444. . That is, the second arm 444 is set to have an optical path length shorter than the first arm 443 by a length corresponding to 1 / B because the first arm 443 includes the optical transmission path 445.

  The phase shift unit 446 changes the phase shift amount of the optical signal transmitted by the second arm 444 in accordance with a control voltage input from the outside.

  The directional coupler 447 combines the optical signal output from the first arm 443 and the optical signal output from the second arm 443, and further separates and outputs the two signals having a phase difference of π. .

  Next, operations of the background art DPSK optical transmitter and DPSK optical receiver shown in FIGS. 1 and 2 will be described.

  The DPSK optical transmitter 100 shown in FIG. 1 receives 16 signals with a low bit rate (for example, 2.5 Gbps). These signals are input to a 16: 2 multiplexer 316. A signal is input to the 16: 2 multiplexer 316 via, for example, SFI-5IF, which is a standard interface used for 40 Gbps data transfer.

  The 16: 2 multiplexer 316 multiplexes 16 received 2.5 Gbps signals every 8 to generate two signals with a bit rate of 20 Gbps, and outputs the generated signals to the 2: 1 multiplexer 202. To do.

  The 2: 1 multiplexer 202 multiplexes two signals having a bit rate of 20 Gbps output from the 16: 2 multiplexer 316, generates a signal D having a bit rate of 40 Gbps, and outputs the signal D to the LN modulator driver 211. Note that 40 Gbps is also the bit rate of the transmission signal output from the DPSK optical transmission apparatus 100 of FIG.

  The LN modulator driver 211 amplifies the amplitude of the signal D to a necessary voltage by 0-π modulation and outputs the amplified signal to the LN modulator 401 as a drive signal.

  The laser diode 215 is a light source that generates light used as a carrier wave (hereinafter referred to as an optical carrier wave), and output light from the laser diode 215 is supplied to the LN modulator 401.

  The LN modulator 401 outputs modulated light by shifting the phase of the optical carrier wave output from the laser diode 215 to 0 or π according to the drive signal output from the LN modulator driver 211.

  A constellation 225 shown in FIG. 1 indicates the phase of a general DPSK signal (transmission signal output from the DPSK optical transmission apparatus). As indicated by constellation 225, the phase of the DPSK signal is 0 or π for each sample.

  When the DPSK optical receiver 107 shown in FIG. 2 receives an optical signal with a bit rate of 40 Gbps, the optical signal is input to the 1-bit delay interferometer 441.

  The 1-bit delay interferometer 441 branches the input optical signal and outputs it to the first arm 443 and the second arm 444. The first arm 443 includes an optical transmission line 445 that delays the optical signal by time T = τ = 1 / B = 25 ps with respect to the second arm 444. Therefore, in the directional coupler 447, the optical signal input through the second arm 444 interferes with the optical signal of one bit before input through the first arm 443. At this time, the directional coupler 447 outputs a differential optical signal having a light intensity corresponding to the phase difference between the two input optical signals. That is, the 1-bit delay interferometer 441 outputs an optical signal having a binary light intensity corresponding to the phase of the input optical signal.

  The balanced optical-electrical signal converter 442 converts the differential optical signal output from the 1-bit delay interferometer 441 into an electrical signal D.

  The 1: 2 demultiplexer 247 separates the electric signal D output from the balanced optical-electrical signal converter 442 into two signals having a bit rate of 20 Gbps.

  The 2:16 demultiplexer 248 separates the two signals output from the 1: 2 demultiplexer 247 into eight signals each having a bit rate of 2.5 Gbps.

  Next, configurations of a DQPSK modulation type optical transmission apparatus (hereinafter referred to as a DQPSK optical transmission apparatus) and a DQPSK modulation type optical reception apparatus (hereinafter referred to as a DQPSK optical reception apparatus) will be described.

  FIG. 3 is a block diagram showing a configuration of a background DQPSK optical transmitter, and FIG. 4 is a block diagram showing a configuration of a background DQPSK optical receiver. FIGS. 3 and 4 show configuration examples of a DQPSK optical transmitter and a DQPSK optical receiver according to the background art that transmit and receive an optical signal with a bit rate B of 40 Gbps.

  As shown in FIG. 3, the DQPSK optical transmission apparatus 101 of the background art includes a 16: 2 multiplexer 316, a laser diode 215, a first LN modulator driver 421, a first LN modulator driver 422, and an LN modulator 410. It is the composition which has.

  The LN modulator 410 includes a first arm 431, a second arm 432, a first Mach-Zehnder type modulator 411, a second Mach-Zehnder type modulator 412, and a phase shift unit 413. The first Mach-Zehnder type modulator 411 is provided on the first arm 431, and the second Mach-Zehnder type modulator 412 is provided on the second arm 432. The phase shift unit 413 is disposed after the two Mach-Zehnder modulators 412 of the second arm 432.

  As shown in FIG. 4, the background art DQPSK optical receiver 108 includes an optical splitter 240, a first delay interferometer 241, a second delay interferometer 242, a first balanced optical-electrical signal converter 453, The configuration includes a second balanced photoelectric signal converter 454 and a 2:16 demultiplexer 248.

  The first delay interferometer 241 includes a first arm 251, a second arm 252, an optical transmission line 256, a phase shift unit 255, and a directional coupler 253. The optical transmission path 256 is provided in the first arm 251, and the phase shift unit 255 is provided in the second arm 252.

  The second delay interferometer 242 includes a first arm 261, a second arm 262, an optical transmission line 266, a phase shift unit 265, and a directional coupler 263. The optical transmission line 266 is provided in the first arm 261, and the phase shift unit 265 is provided in the second arm 262.

  Next, operations of the DQPSK optical transmitter and the DQPSK optical receiver of the background art will be described.

  The DQPSK optical transmission apparatus 101 illustrated in FIG. 3 receives 16 signals with a low bit rate (for example, 2.5 Gbps). These signals are input to a 16: 2 multiplexer 316. A signal is input to the 16: 2 multiplexer 316 via, for example, SFI-5IF, which is a standard interface used for data transfer of 40 Gbps.

  The 16: 2 multiplexer 316 multiplexes the received 16 2.5 Gbps signals every 8 to generate two signals D1 and D2 having a bit rate of 20 Gbps. Note that the bit rate of the transmission signal of the DQPSK optical transmission apparatus 101 shown in FIG. 3 is 40 Gbps. Therefore, the bit rates of the signals D1 and D2 are 20 Gbps, which is a half bit rate of the transmission signal.

  The 16: 2 multiplexer 316 outputs the generated one signal D1 to the first LN modulator driver 421, and outputs the other signal D2 to the second LN modulator driver 422.

  The first LN modulator driver 421 amplifies the amplitude of the signal D1 output from the 16: 2 multiplexer 316 to a required amplitude by 0-π modulation, and supplies the amplified signal to the first Mach-Zehnder type modulator 411 as a drive signal. Output.

  The second LN modulator driver 422 amplifies the amplitude of the signal D2 output from the 16: 2 multiplexer 316 to a necessary amplitude by 0-π modulation, and supplies the amplified signal to the second Mach-Zehnder type modulator 412 as a drive signal. Output.

  The laser diode 215 is a light source that generates an optical carrier wave used as a carrier wave, and the output light of the laser diode 215 is supplied to the LN modulator 410.

  The LN modulator 410 branches the optical carrier wave output from the laser diode 215 and outputs it to the first arm 431 and the second arm 432.

  The first Mach-Zehnder type modulator 411 included in the first arm 431 and the second Mach-Zehnder type modulator 412 included in the second arm 432 include the corresponding first LN modulator driver 421 or the second The modulated light is output by shifting the phase of the optical carrier wave output from the laser diode 215 to 0 or π in accordance with the drive signal output from the LN modulator driver 422.

  Further, in the second arm 432, the phase shift amount of the optical signal by the phase shift unit 413 is set to π / 2 according to the value of the bias A. For this reason, the optical signal output from the second Mach-Zehnder type modulator 412 is combined (combined) with the optical signal output from the first arm 431 after the phase is shifted by π / 2. The

  Reference numerals 415 and 416 in FIG. 3 denote optical signal constellations having a binary phase before being combined. That is, 415 indicates a constellation of the optical signal output from the first arm 431, and 416 indicates a constellation of the optical signal output from the second arm 432.

  Further, reference numeral 226 in FIG. 3 represents a constellation of an optical signal having a quaternary phase in which the optical signal output from the first arm 431 and the optical signal output from the second arm 432 are combined. .

  The constellation 226 indicates the phase of a general DQPSK signal, and the phase of the DQPSK signal is π / 4, 3π / 4, 5π / 4, or 7π / 4 for each sample. Since this DQPSK signal has information of 4 values = 2 bits per sample, when the bit rate B = 40 Gbps, the sample rate is 20 Gsps.

  When the DQPSK optical receiver 108 shown in FIG. 4 receives an optical signal (bit rate B = 40 Gbps, sample rate = 20 Gsps), the optical signal is input to the optical splitter 240.

  The optical splitter 240 branches the input optical signal and outputs it to the first delay interferometer 241 and the second delay interferometer 242.

  The first delay interferometer 241 branches the input optical signal and outputs it to the first arm 251 and the second arm 252. The optical transmission path 256 included in the first arm 251 is configured to change the optical signal transmitted by the first arm 251 to a time corresponding to one sample T = 2τ = 2 with respect to the optical signal transmitted by the second arm 252. Delay / B = 50 ps. That is, the second arm 252 is set to have an optical path length shorter than the first arm 251 by a length corresponding to 2 / B because the first arm 251 includes the optical transmission path 256. In the DQPSK modulation method, the sample interval is doubled compared to the DPSK modulation method, so the delay time required for interference with the signal one sample before is twice that of the DPSK modulation method.

  In the second arm 252, the phase shift amount of the optical signal transmitted by the second arm 252 is set to π / 4 by the phase shift unit 255.

  In the directional coupler 253, the optical signal whose phase is shifted by π / 4 in the second arm 252 interferes with the optical signal of 1 symbol = 50 ps output from the first arm 251. At this time, the directional coupler 253 outputs a differential optical signal having a light intensity corresponding to the phase difference between the two input optical signals. That is, the first delay interferometer 241 outputs an optical signal having a binary light intensity corresponding to the phase of the input optical signal.

  The first balanced optical-electrical signal converter 453 converts the differential optical signal output from the first delay interferometer 241 into an electrical signal D1 and outputs it.

  The second delay interferometer 242 branches the input optical signal and outputs it to the first arm 261 and the second arm 262. The optical transmission path 266 included in the first arm 261 is configured to change the optical signal transmitted by the first arm 261 to a time corresponding to one sample T = 2τ = 2 with respect to the optical signal transmitted by the second arm 262. Delay / B = 50 ps. That is, the second arm 262 is set to have an optical path length shorter than the first arm 261 by a length corresponding to 2 / B because the first arm 261 includes the optical transmission path 266.

  In the second arm 262, the phase shift amount of the optical signal transmitted from the second arm 262 by the phase shift unit 265 is set to −π / 4.

  In the directional coupler 263, the optical signal whose phase is shifted by −π / 4 in the second arm 262 interferes with the optical signal output from the first arm 261 of 1 symbol = 50 ps before. At this time, the directional coupler 263 outputs a differential optical signal having a light intensity corresponding to the phase difference between the two input optical signals. That is, the second delay interferometer 242 outputs an optical signal having a binary light intensity corresponding to the phase of the input optical signal.

  The second balanced optical-electrical signal converter 454 converts the differential optical signal output from the second delay interferometer 242 into an electrical signal D2 and outputs it.

  The 2:16 demultiplexer 248 separates the signal D1 output from the first balanced optical-electrical signal converter 453 into eight signals with a bit rate of 2.5 Gbps, and outputs the second balanced optical signal. The signal D2 output from the electric signal converter 454 is separated into eight signals with a bit rate of 2.5 Gbps and output.

  As described above, since the DPSK modulation method and the DQPSK modulation method have different advantages, it is desirable that the DPSK modulation method and the DQPSK modulation method can be switched in accordance with various conditions in an optical communication system.

  FIG. 5 is a block diagram showing a configuration of an optical communication system 1000 of the background art that can use the DPSK modulation method and the DQPSK modulation method.

As shown in FIG. 5, the optical communication system 1000 of the background art includes a DPSK optical transmission device 100, a DQPSK optical transmission device 101, an optical switch 102, an optical switch 106, a DPSK optical reception device 107, and a DQPSK optical reception device 108.
The DPSK optical transmission device 100 and the DQPSK optical transmission device 101 are connected to the DPSK optical reception device 107 and the DQPSK optical reception device 108 via the optical switch 102, the optical switch 106, and the optical network 105.

  In the optical communication system 1000 of the background art shown in FIG. 5, when the DPSK modulation method is used, the optical signal output from the DPSK optical transmitter 100 by the optical switch 102 is transmitted to the optical network 105, and the optical signal received from the optical network 105 is received. The signal is output to the DPSK optical receiver 107 by the optical switch 106.

  When the DQPSK modulation method is used, an optical signal output from the DQPSK optical transmitter 101 by the optical switch 102 is transmitted to the optical network 105, and an optical signal received from the optical network 105 is transmitted to the DQPSK optical receiver by the optical switch 106. To 108.

  As shown in FIG. 5, the optical communication system 1000 of the background art includes a DPSK transmission apparatus and a DPSK optical reception apparatus corresponding only to the DPSK modulation scheme, and a DQPSK transmission apparatus and a DQPSK optical reception apparatus corresponding only to the DQPSK modulation scheme. Furthermore, it is necessary to provide switching means such as an optical switch for switching the connection between these transmission / reception devices.

  Therefore, the optical communication system 1000 of the background art is not suitable for downsizing and cost reduction.

JP-T-2004-516743

G. Charlet, et al., “Efficient Mitigation of Fiber Impairments in an Ultra−Long Haul Transmission of 40Gbit / s Polarization−Multiplexed Data By Digital Processing in a Coherent Receiver”, Optical Fiber Communication Conference, 2007 Optical Society of America, PDP17 J.-X. Cai, et al., “Experimental Comparison of DPSK and OOK Modulation Formats over Slope-Matched Fiver Spans”, Optical Fiber Communication Conference, 2004 Optical Society of America, FMI R. A. Griffin, et al., “Optical Differential Quadrature Phase-Shift Key (oDQPSK) for High Capacity Optical Transmission”, Optical Fiber Communication Conference and Exhibit, OFC 2002, WX6, pp.367

  Accordingly, an object of the present invention is to provide an optical transmitter, an optical receiver, and an optical communication system that can use two modulation schemes, DPSK and DQPSK.

In order to achieve the above object, the optical transmission apparatus of the present invention has the bit rate of the optical signal to be transmitted as B,
A first selector that selects and outputs a first signal having a bit rate of B or a second signal having a bit rate of B / 2;
A second selector that selects and outputs a third signal having a bit rate of B, a fourth signal having a bit rate of B / 2, or a fifth signal having a constant voltage;
A light source that generates an optical carrier;
First and second Mach-Zehnder type modulators for branching the optical carrier wave, modulating the branched optical carrier wave and outputting the modulated carrier wave;
A phase shift unit that shifts the phase of the optical signal output from the second Mach-Zehnder modulator;
A first modulation driver that drives the first Mach-Zehnder modulator according to a signal output from the first selector;
A second modulation driver that drives the second Mach-Zehnder modulator according to a signal output from the second selector;
An optical signal combining unit that combines an optical signal output from the first Mach-Zehnder modulator and an optical signal output from the phase shift unit, and outputs the optical signal as the transmission signal;
A controller that controls the first selector, the second selector, the second Mach-Zehnder modulator, and the phase shift unit;
Have
The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Causing the first selector to select the first signal, causing the second selector to select the third or fifth signal,
When transmitting an optical signal modulated by the DQPSK modulation method,
The first selector is configured to select the second signal, and the second selector is configured to select the fourth signal.

Or, when the bit rate of the optical signal to be transmitted is B,
A first selector that selects and outputs a first signal having a bit rate of B or a second signal having a bit rate of B / 2;
A second selector for selecting and outputting a fourth signal having a bit rate of B / 2 or a fifth signal having a constant voltage;
A light source that generates an optical carrier;
First and second Mach-Zehnder type modulators for branching the optical carrier wave, modulating the branched optical carrier wave and outputting the modulated carrier wave;
A phase shift unit that shifts the phase of the optical signal output from the second Mach-Zehnder modulator;
A first modulation driver that drives the first Mach-Zehnder modulator according to a signal output from the first selector;
A second modulation driver that drives the second Mach-Zehnder modulator according to a signal output from the second selector;
An optical signal combining unit that combines an optical signal output from the first Mach-Zehnder modulator and an optical signal output from the phase shift unit, and outputs the optical signal as the transmission signal;
A controller that controls the first selector, the second selector, the second Mach-Zehnder modulator, and the phase shift unit;
Have
The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Causing the first selector to select the first signal, causing the second selector to select the fifth signal,
When transmitting an optical signal modulated by the DQPSK modulation method,
The first selector is configured to select the second signal, and the second selector is configured to select the fourth signal.

Or, when the bit rate of the optical signal to be transmitted is B,
A first selector that selects and outputs a first signal having a bit rate of B or a second signal having a bit rate of B / 2;
A second selector for selecting and outputting a third signal having a bit rate of B or a fourth signal having a bit rate of B / 2;
A light source that generates an optical carrier;
First and second Mach-Zehnder type modulators for branching the optical carrier wave, modulating the branched optical carrier wave and outputting the modulated carrier wave;
A phase shift unit that shifts the phase of the optical signal output from the second Mach-Zehnder modulator;
A first modulation driver that drives the first Mach-Zehnder modulator according to a signal output from the first selector;
A second modulation driver that drives the second Mach-Zehnder modulator according to a signal output from the second selector;
An optical signal combining unit that combines an optical signal output from the first Mach-Zehnder modulator and an optical signal output from the phase shift unit, and outputs the optical signal as the transmission signal;
A controller that controls the first selector, the second selector, the second Mach-Zehnder modulator, and the phase shift unit;
Have
The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Causing the first selector to select the first signal, causing the second selector to select the third signal,
When transmitting an optical signal modulated by the DQPSK modulation method,
The first selector is configured to select the second signal, and the second selector is configured to select the fourth signal.

On the other hand, the optical receiver of the present invention has a bit rate of the received optical signal as B,
An optical splitter for branching the received optical signal into two;
The first arm, the second arm shorter than the first arm by a length corresponding to 2 / B, and the second arm to which the input optical signal is further branched and input An optical signal having a binary optical intensity corresponding to the phase of the optical signal, the optical signal branched by the optical splitter. A first delay interferometer that converts to
The third arm to which the input optical signal is further branched and input, the fourth arm whose optical path length is shorter than the third arm by a length corresponding to 2 / B, and the fourth arm A second phase shift unit that shifts the phase of the transmitted optical signal, and converts the other optical signal branched by the optical splitter into an optical signal having a binary light intensity corresponding to the phase of the optical signal. A second delay interferometer to convert;
A first optical-electrical signal converter that converts an optical signal output from the first delay interferometer into an electrical signal;
A second optical-electrical signal converter that converts an optical signal output from the second delay interferometer into an electrical signal;
A control unit for controlling the first phase shift unit and the second phase shift unit;
Have
The controller is
When receiving an optical signal modulated by the DPSK modulation method,
A phase shift amount by the first phase shift unit is set to 0;
When receiving an optical signal modulated by the DQPSK modulation method, the phase shift amount by the first phase shift unit is set to + π / 4, and the phase shift amount by the second phase shift unit is set to −π / 4. It is the structure to do.

  The optical communication system of the present invention includes any one of the above-described optical transmission devices and the optical reception device.

FIG. 1 is a block diagram showing a configuration of a background art DPSK optical transmission apparatus. FIG. 2 is a block diagram showing a configuration of a background art DPSK optical receiver. FIG. 3 is a block diagram showing a configuration of a DQPSK optical transmission apparatus according to the background art. FIG. 4 is a block diagram showing a configuration of a DQPSK optical receiver according to the background art. FIG. 5 is a block diagram illustrating a configuration of an optical communication system according to the background art. FIG. 6 is a block diagram illustrating a configuration example of the optical transmission apparatus according to the first embodiment. FIG. 7 is a block diagram illustrating a configuration example of the optical receiving apparatus according to the first embodiment. FIG. 8 is a block diagram illustrating a configuration example of the optical communication system according to the first embodiment. FIG. 9 is a block diagram illustrating a configuration example of the optical transmission apparatus according to the second embodiment. FIG. 10 is a block diagram illustrating a configuration example of the optical transmission apparatus according to the second embodiment. FIG. 11 is a block diagram illustrating a configuration example of the optical receiving apparatus according to the second embodiment. FIG. 12 is a block diagram illustrating a configuration example of the optical receiving apparatus according to the second embodiment. FIG. 13 is a block diagram illustrating a configuration example of the optical transmission apparatus according to the third embodiment. FIG. 14 is a block diagram illustrating a configuration example of the optical receiving apparatus according to the third embodiment.

  Next, the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 6 is a block diagram illustrating a configuration example of the optical transmission apparatus according to the first embodiment, and FIG. 7 is a block diagram illustrating a configuration example of the optical reception apparatus according to the first embodiment. FIG. 8 is a block diagram illustrating a configuration example of the optical communication system according to the first embodiment.

  First, the configuration of the optical transmission device 1 according to the first embodiment will be described.

  The optical transmission device 1 of the present invention has a configuration capable of transmission using the DPSK modulation method and the DQPSK modulation method, respectively.

  As shown in FIG. 6, the optical transmission device 1 of the first embodiment includes a 2: 1 multiplexer 202, a first selector 207, a second selector 208, a first LN modulator driver 211, a second The configuration includes an LN modulator driver 212, a laser diode 215, a modulation unit 217, and a control unit 250.

  The optical transmission apparatus 1 according to the first embodiment receives signals D1 and D2 whose bit rate is 1/2 (= B / 2) of the bit rate B of the transmission signal. For example, when the bit rate B of the transmission signal of the optical transmission device 1 is 40 Gbps, the bit rate B / 2 of the signals D1 and D2 is 20 Gbps.

  The signal D1 is input to the 2: 1 multiplexer 202 and the first selector 207, and the signal D2 is input to the 2: 1 multiplexer 202 and the second selector 208.

  The 2: 1 multiplexer 202 multiplexes the signal D1 and the signal D2, and generates a signal D whose bit rate is the bit rate B of the transmission signal and a signal Db that is an inverted signal thereof. The 2: 1 multiplexer 202 outputs the signal D to the first selector 207 and outputs the signal Db to the second selector 208.

  The first selector 207 is a selection circuit for selecting a signal to be supplied to the first LN modulator driver 211. The first selector 207 selects either the signal D1 or the signal D according to the first control signal output from the control unit 250, and outputs the selected signal to the first LN modulator driver 211. .

  The second selector 208 is a selection circuit for selecting a signal to be supplied to the second LN modulator driver 212. To the second selector 208, the signal D2 and the signal Db are input, and the constant voltage DC is input. The second selector 208 selects one of the signals D2, Db and DC (constant voltage DC) in accordance with the second control signal output from the control unit 250, and selects the selected signal as the second LN. Output to modulator driver 212.

  The first LN modulator driver 211 amplifies the amplitude of the signal output from the first selector 207 to a necessary amplitude by 0-π modulation, and uses the modulator 217 (first Mach-Zehnder described later) as a drive signal. Type modulator 213).

  The second LN modulator driver 212 amplifies the amplitude of the signal output from the second selector 208 to a required amplitude by 0-π modulation, and uses the modulation unit 217 (second Mach-Zehnder described later) as a drive signal. Type modulator 214).

  The laser diode 215 is a light source that generates an optical carrier wave to be used as a carrier wave, and output light from the laser diode 215 is supplied to the modulation unit 217.

  The modulation unit 217 includes a first arm 231, a second arm 232, a branching unit 221, a first Mach-Zehnder modulator 213, a second Mach-Zehnder modulator 214, a phase shift unit 218, and an optical signal. A synthesizer 222 is provided.

  The first arm 231 and the second arm 232 are set to have the same optical path length.

  The branching unit 221 branches the optical carrier wave output from the laser diode 215 and outputs the optical carrier wave with equal intensity to the first arm 231 and the second arm 232.

  The first arm 231 includes a first Mach-Zehnder type modulator 213, and the second arm 232 includes a second Mach-Zehnder type modulator 214 and a phase shift unit 218, and the second Mach-Zehnder type A phase shift unit 218 is disposed after the modulator 214.

  A drive signal output from the first LN modulator driver 211 is input to the first Mach-Zehnder type modulator 213, and a second LN modulator driver 212 is input to the second Mach-Zehnder type modulator 214. The drive signal output from is input. Note that the second Mach-Zehnder type modulator 214 receives an LN bias for adjusting the transmittance from the control unit 250.

  The phase shift unit 218 changes the phase shift amount of the optical signal transmitted by the second arm 232 according to the value of the bias A output from the control unit 250.

  The optical signal combining unit 222 combines the optical signals output from the first arm 231 and the second arm 232, and outputs the combined optical signal as a transmission signal.

  The modulation unit 217 outputs modulated light by changing the phase of the optical carrier according to the drive signals output from the first LN modulator driver 211 and the second LN modulator driver 212.

  The control unit 250 controls the selection operation of the first selector 207 and the second selector 208, the transmittance of the second Mach-Zehnder type modulator 214, and the phase shift amount of the optical signal by the phase shift unit 218.

  Next, the configuration of the optical receiver 2 according to the first embodiment will be described.

  The optical receiver 2 according to the first embodiment is configured to receive optical signals modulated by the DPSK modulation method and the DQPSK modulation method.

  As shown in FIG. 7, the optical receiver 2 of the first embodiment includes an optical splitter 240, a first delay interferometer 241, a second delay interferometer 242, and a first balanced optical-electrical signal conversion. 243, second balanced optical-electrical signal converter 244, 1: 2 demultiplexer 247, first selector 245, second selector 246, and control unit 280.

  The optical splitter 240 branches the received signal and outputs it to the first delay interferometer 241 and the second delay interferometer 242 with equal intensity.

  The first delay interferometer 241 includes a first arm 251, a second arm 252, an optical transmission line 256, a phase shift unit 255, and a directional coupler 253.

  The optical transmission path 256 included in the first arm 251 is configured to change the optical signal transmitted by the first arm 251 to a time corresponding to one sample T = 2τ = 2 with respect to the optical signal transmitted by the second arm 252. Delay / B = 50 ps. That is, the second arm 252 is set to have an optical path length shorter than the first arm 251 by a length corresponding to 2 / B because the first arm 251 includes the optical transmission path 256.

  The phase shift unit 255 changes the phase shift amount of the optical signal transmitted by the second arm 252 according to the first control voltage output from the control unit 280.

  The directional coupler 253 combines the optical signal output from the first arm 251 and the optical signal output from the second arm 252, and further separates and outputs the two signals having a phase difference of π. .

  The second delay interferometer 242 includes a first arm 261, a second arm 262, an optical transmission line 266, a phase shift unit 265, and a directional coupler 263.

  The optical transmission path 266 included in the first arm 261 is configured to change the optical signal transmitted by the first arm 261 to a time corresponding to one sample T = 2τ = 2 with respect to the optical signal transmitted by the second arm 262. Delay / B = 50 ps. That is, the second arm 262 is set to have an optical path length shorter than the first arm 261 by a length corresponding to 2 / B because the first arm 261 includes the optical transmission path 266.

  The phase shift unit 265 changes the phase shift amount of the optical signal transmitted by the second arm 262 according to the second control voltage output from the control unit 280.

  The directional coupler 263 combines the optical signal output from the first arm 261 and the optical signal output from the second arm 262, and further separates and outputs the two signals having a phase difference of π. .

  The first balanced optical-electrical signal converter 243 converts the optical signal output from the first delay interferometer 241 into an electrical signal, and the second balanced optical-electrical signal converter 244 performs the second delay. The optical signal output from the interferometer 242 is converted into an electrical signal.

  The 1: 2 demultiplexer 247 divides the signal output from the first balanced optical-electrical signal converter 243 into two signals having a half bit rate and outputs the separated signal. For example, when a transmission signal having a bit rate B is input, two signals having a bit rate B / 2 are output.

  The first selector 245 is a signal output from the 1: 2 demultiplexer 247 or a signal output from the first balanced optical-electrical signal converter 243 in accordance with the first control signal output from the control unit 280. Either one is selected and output.

  The second selector 246 is configured to output a signal output from the 1: 2 demultiplexer 247 or a signal output from the second balanced optical-electrical signal converter 244 according to the second control signal output from the control unit 280. Either one is selected and output.

  Note that the optical receiver 2 of this embodiment is designed so that the signals branched into two paths by the optical splitter 240 arrive at the first selector 245 and the second selector 246 at the same timing. To do.

  The control unit 280 controls the selection operation by the first selector 245 and the second selector 246 and the phase shift amount of the optical signal by the phase shift units 255 and 265.

  Next, the configuration of the optical communication system 3 according to the first embodiment will be described.

  The optical communication system 3 of the present embodiment has a configuration that can be used by switching between the DPSK modulation method and the DQPSK modulation method.

  As shown in FIG. 8, the optical communication system 3 of the first embodiment includes an optical transmission device 1 and an optical reception device 2, and the optical transmission device 1 and the optical reception device 2 are connected via an optical network 4. It is a configuration.

  First, the operation (transmission operation) of the optical transmission device 1 according to the first embodiment will be described with reference to FIG.

  In the optical transmission device 1 of the present embodiment, a signal D1 having a bit rate of B / 2 is input to the first selector 207 and the 2: 1 multiplexer 202, and a signal D2 having a bit rate of B / 2 is input to the second selector. Input to 208 and 2: 1 multiplexer 202.

  The 2: 1 multiplexer 202 generates a signal D equal to the bit rate B of the transmission signal and a signal Db which is an inverted signal of the signal D by bit-multiplexing the two input signals D1 and D2. The 2: 1 multiplexer 202 outputs a signal D to the first selector 207 and outputs a signal Db to the second selector 208.

  The operation up to this point is common to the DQPSK modulation method and the DPSK modulation method. The subsequent operation will be described below separately for the case of using the DQPSK modulation method and the case of using the DPSK modulation method.

  First, the transmission operation when the DQPSK modulation method is used will be described.

  In this case, the first selector 207 selects the signal D1 having a bit rate of B / 2 according to the first control signal output from the control unit 250, and uses the selected signal D1 as the first LN modulator driver 211. Output to.

  The second selector 208 selects the signal D2 having a bit rate of B / 2 according to the second control signal output from the control unit 250, and outputs the selected signal D2 to the second LN modulator 212.

  The first LN modulator driver 211 amplifies the signal D1 output from the first selector 207 to a necessary amplitude by 0-π modulation, and outputs the amplified signal to the first Mach-Zehnder type modulator 213 as a drive signal. .

  The second LN modulator driver 212 amplifies the signal D2 output from the second selector 208 to a necessary amplitude by 0-π modulation, and outputs the amplified signal to the second Mach-Zehnder modulator 214 as a drive signal. .

  The branching unit 221 of the modulation unit 217 branches the optical carrier wave output from the laser diode 215 and outputs two lights having the same intensity to the first arm 231 and the second arm 232.

  The first Mach-Zehnder type modulator 213 shifts the phase of the optical carrier wave output from the laser diode 215 to 0 or π according to the drive signal output from the first LN modulator driver 211 (0− π modulation). Similarly, the second Mach-Zehnder modulator 214 shifts the phase of the optical carrier wave output from the laser diode 215 to 0 or π according to the drive signal output from the second LN modulator driver 212. (0-π modulation). Here, in the second arm 232, the phase of the optical signal transmitted by the phase shift unit 218 is further shifted by π / 2.

  The optical signal combining unit 222 combines the optical signal transmitted by the first arm 231 and the optical signal transmitted by the second arm 232, and outputs the resultant as a transmission signal.

  Reference numeral 226 in FIG. 6 indicates a constellation of an optical signal having a quaternary phase obtained by combining the optical signal output from the first arm 231 and the optical signal output from the second arm 232, that is, the DQPSK signal. ing.

  The DQPSK signal is a 40 Gbps signal having a phase of π / 4, 3π / 4, 5π / 4, or 7π / 4 as indicated by the constellation 226, and its sample rate is 20 Gsps.

  The transmission operation when the DQPSK modulation method of the optical transmission apparatus 1 of the first embodiment is used is a 2: 1 multiplexer added before the first LN modulator driver 211 and the second LN modulator driver 212. The operation is the same as that of the DQPSK transmission apparatus 101 of the background art shown in FIG. 3 except for the operations of 202, the first selector 207, and the second selector 208.

  Next, the transmission operation when the DPSK modulation method is used will be described.

  When DPSK modulation is used, the first selector 207 selects the signal D according to the first control signal output from the control unit 250 and outputs the selected signal D to the first LN modulator driver 211.

  The second selector 208 selects the signal Db or the constant voltage DC according to the second control signal output from the control unit 250, and outputs the selected signal Db or DC to the second LN modulator driver 212.

  When the constant voltage DC is output from the second selector 208, the output amplitude of the second LN modulator driver 212 is zero. Further, the control unit 250 sets the value of the LN bias supplied to the modulation unit 214 so that the transmittance of the second Mach-Zehnder type modulator 214 becomes zero.

  In this case, since the second Mach-Zehnder type modulator 214 blocks the optical carrier wave of the laser diode 215, the phase modulated from the modulation unit 217 by the first Mach-Zehnder type modulator 213 has a binary value. Only the signal is output. That is, the optical transmission device 1 illustrated in FIG. 6 outputs a DPSK signal having a binary phase indicated by a constellation 225 as a transmission signal.

  On the other hand, when the inverted signal Db is output from the second selector 208, the second Mach-Zehnder modulator 214 outputs a signal obtained by modulating the optical carrier wave by 0-π. This signal is a signal whose phase is inverted with respect to the signal that is 0-π modulated by the first Mach-Zehnder type modulator 213. In addition, the phase shift amount of the optical signal by the phase shift unit 218 is set to π according to the value of the bias A output from the control unit 250.

  In this case, a binary DPSK signal having the same phase is output from the first arm 231 and the second arm 232, and an optical signal obtained by combining (adding) these signals is output from the optical signal combining unit 222. . That is, a DPSK signal having twice the strength of the background art optical transmitter shown in FIG. 1 is output.

  A constellation 225 illustrated in FIG. 6 indicates the phase of the DPSK signal (transmission signal output from the optical transmission device 1) output from the optical transmission device 1 according to the first embodiment. As indicated by constellation 225, the phase of the DPSK signal is 0 or π for each sample.

  Next, the reception operation of the optical receiver 2 according to the first embodiment will be described with reference to FIG.

  First, the reception operation when the DQPSK modulation method is used will be described.

  When the optical receiver 2 of this embodiment receives a DQPSK signal (optical signal), the optical signal is input to the optical splitter 240.

  The optical splitter 240 branches the received optical signal and outputs it to the first delay interferometer 241 and the second delay interferometer 242.

  The first delay interferometer 241 branches the input optical signal and outputs it to the first arm 251 and the second arm 252.

  The optical transmission path 256 provided in the first arm 251 transmits the optical signal transmitted by the first arm 251 to the optical signal transmitted by the second arm 252 at a time T = 2τ = 2 / B = 50 ps. Just delay.

  The phase shift unit 255 provided in the second arm 252 sets the phase shift amount of the optical signal transmitted by the second arm 252 to π / 4 according to the first control voltage output from the control unit 280.

  The directional coupler 253 combines the optical signal output from the first arm 252 and the optical signal output from the second arm 252, and further separates and outputs the two signals having a phase difference of π. . At this time, in the directional coupler 253, an optical signal output from the second arm 252 is shifted in phase by π / 4, the bit rate is B / 2 sps, and the phase is quaternary. One symbol = 50 ps before the optical signal output from the arm 251 interferes. As a result, the directional coupler 253 outputs a differential optical signal having a binary light intensity corresponding to the phase difference between these two optical signals. That is, the first delay interferometer 241 outputs an optical signal having a binary light intensity corresponding to the phase of the input optical signal.

  The first balanced optical-electrical signal converter 243 converts the differential optical signal output from the first delay interferometer 241 into an electrical signal and outputs it to the 1: 2 demultiplexer 247 and the first selector 245. To do.

  The 1: 2 demultiplexer 247 separates the signal output from the first balanced optical-electrical signal converter 243 for each bit, and generates two signals with a bit rate of B / 2, one of which is the first 1 is output to the selector 245 and the other is output to the second selector 246.

  The first selector 245 includes a first balanced optical-electrical signal converter out of the signal output from the first balanced optical-electrical signal converter 243 and the signal output from the 1: 2 demultiplexer 247. A signal with a bit rate of B / 2 output from 243 is selected and output as a signal D3.

  The second delay interferometer 242 branches the input optical signal and outputs it to the first arm 261 and the second arm 262.

  The optical transmission path 266 included in the first arm 261 is configured to transmit the optical signal transmitted by the first arm 261 to the optical signal transmitted by the second arm 262 at a time T = 2τ = 2 / B = 50 ps. Just delay.

  The phase shift unit 265 included in the second arm 262 sets the phase shift amount of the optical signal transmitted by the second arm 262 to −π / 4 according to the second control voltage output from the control unit 280.

  The directional coupler 263 combines the optical signal output from the first arm 262 and the optical signal output from the second arm 262, and further separates and outputs the two signals having a phase difference of π. . At this time, in the directional coupler 263, the optical signal output from the second arm 262 is shifted in phase by −π / 4, the bit rate is B / 2 sps, and the phase is quaternary. 1 symbol = 50 ps before the optical signal output from the arm 261 interferes. As a result, the directional coupler 263 outputs a differential optical signal with a bit rate of B / 2 having a binary light intensity corresponding to the phase difference between the two input optical signals. That is, the second delay interferometer 242 outputs an optical signal having a binary light intensity corresponding to the phase of the input optical signal.

  The second balanced optical-electrical signal converter 244 converts the differential optical signal output from the second delay interferometer 242 into an electrical signal and outputs it to the second selector 246.

  The second selector 246 includes a second balanced optical-electrical signal converter out of the signal output from the second balanced optical-electrical signal converter 244 and the signal output from the 1: 2 demultiplexer 247. A signal with a bit rate of B / 2 output from 244 is selected and output as signal D4.

  The reception operation in the case of using the DQPSK modulation method of the optical receiver 2 of the first embodiment is that the output signal of the first balanced optical-electrical signal converter 243 is branched and the 1: 2 demultiplexer. The operation is the same as that of the DQPSK receiving apparatus of the background art shown in FIG. 4 except for the operation by the first selector 207 and the second selector 208.

  Next, the reception operation when using the DPSK modulation method will be described.

  When the optical receiver 2 of the present embodiment receives a DPSK signal (optical signal), the optical signal is input to the optical splitter 240 as in the case of receiving a DQPSK signal.

  The optical splitter 240 branches the received optical signal and outputs it to the first delay interferometer 241 and the second delay interferometer 242.

  The first delay interferometer 241 branches the input optical signal and outputs it to the first arm 251 and the second arm 252.

  The optical transmission path 256 provided in the first arm 251 transmits the optical signal transmitted by the first arm 251 to the optical signal transmitted by the second arm 252 at a time T = 2τ = 2 / B = 50 ps. Just delay.

  The phase shift unit 255 provided in the second arm 252 sets the phase shift amount of the optical signal transmitted by the second arm 252 to 0 according to the first control voltage output from the control unit 280.

  Note that when the DPSK modulation method is used, an optical signal is also input to the second delay interferometer 242, but its output is not selected by the second selector 246. That is, when the DPSK modulation method is used, the optical receiver 2 does not use the second delay interferometer 242.

  When the DPSK modulation method is used, the sample rate of the received DPSK signal is the same as the bit rate B of the received signal.

  The directional coupler 253 combines the optical signal output from the first arm 252 and the optical signal output from the second arm 252, and further separates and outputs the two signals having a phase difference of π. . At this time, in the directional coupler 253, an optical signal having a bit rate of B and a phase of four values output from the second arm 252 and one symbol output from the first arm 251 = 50 ps before. Interfere with other optical signals. As a result, the directional coupler 253 outputs a differential optical signal with a bit rate of B having a binary light intensity corresponding to the phase difference between the two input optical signals.

  The first balanced optical-electrical signal converter 243 converts the differential optical signal output from the first delay interferometer 241 into an electrical signal and outputs it to the 1: 2 demultiplexer 247 and the first selector 245. To do.

  The 1: 2 demultiplexer 247 separates the signal output from the first balanced optical-electrical signal converter 243 for each bit, and generates two signals with a bit rate of B / 2, one of which is the first 1 is output to the selector 245 and the other is output to the second selector 246.

  The first selector 245 is a signal output from the 1: 2 demultiplexer 247 out of the signal output from the first balanced photoelectric signal converter 243 and the signal output from the 1: 2 demultiplexer 247. Is output as a signal D3. The second selector 246 selects the signal output from the 1: 2 demultiplexer 247 and outputs it as the signal D4.

  Next, the operation of the entire optical communication system 3 according to the first embodiment will be described with reference to FIG.

  In the optical communication system 3 of the present embodiment, the optical transmission device 1 transmits a signal to the optical reception device 2 via the optical network 4, and the optical reception device 2 transmits from the optical communication device 1 via the optical network 4. Receive the received signal.

  When a DPSK signal is transmitted from the optical transmitter 1, the optical receiver 2 according to the present embodiment receives the optical signal by a receiving operation corresponding to the above-described DPSK modulation method. When a DQPSK signal is transmitted from the optical transmission device 1, the optical signal is received by a reception operation corresponding to the above-described DQPSK modulation method.

  According to the first embodiment, it is possible to realize the optical transmission device 1 capable of transmitting optical signals of two modulation schemes, namely the DPSK modulation scheme and the DQPSK modulation scheme.

  In addition, the optical transmission device 1 of the present embodiment uses a DPSK modulation method and a DQPSK modulation method, a laser diode 215 that is a light source, a first Mach-Zehnder modulator 213, and a second Mach-Zehnder modulator 214. The first LN modulator driver 211 and the second LN modulator driver 212 can be shared.

  Therefore, it is possible to realize an optical transmission apparatus that can transmit optical signals of two modulation schemes, DPSK modulation scheme and DQPSK modulation scheme, at a small size and at low cost. That is, space saving and cost reduction can be achieved compared to the configuration of the background art that requires separate optical transmitters for the DPSK modulation method and the DQPSK modulation method.

  In addition, according to the first embodiment, it is possible to realize the optical receiver 2 that can receive optical signals of two modulation schemes of the DPSK modulation scheme and the DQPSK modulation scheme.

  Also, the optical receiver 2 of the present embodiment uses the DPSK modulation method and the DQPSK modulation method, the first delay interferometer 241, the second delay interferometer 242, and the first balanced optical-electrical signal converter 243. The second balanced opto-electric signal converter 244 and the 1: 2 demultiplexer 247 can be shared.

  Therefore, the optical receiver 2 capable of receiving optical signals of two modulation schemes, the DPSK modulation scheme and the DQPSK modulation scheme, can be realized in a small size and at a low cost. That is, space saving and cost reduction can be achieved as compared with the configuration of the background art that requires separate optical receivers for the DPSK modulation method and the DQPSK modulation method.

(Second Embodiment)
FIG. 9 and FIG. 10 are block diagrams illustrating a configuration example of the optical transmission apparatus according to the second embodiment. FIG. 9 is a diagram for explaining the operation of the DQPSK modulation method, and FIG. 10 is a diagram for explaining the operation of the DPSK modulation method.

  FIG. 11 and FIG. 12 are block diagrams showing an example of the configuration of the optical receiver according to the second embodiment. FIG. 11 is a diagram for explaining the operation of the DQPSK modulation method, and FIG. 12 is a diagram for explaining the operation of the DPSK modulation method.

  Note that the configuration and operation of the optical communication system according to the second embodiment are the same as those of the optical communication system according to the first embodiment, and a description thereof will be omitted here.

  In the second embodiment, for example, a case where the transmission signal and the reception signal have a bit rate B = 40 Gbps and τ = 1 / B = 25 ps will be described as an example.

  First, the configuration of the optical transmission device 5 according to the second embodiment will be described.

  As shown in FIGS. 9 and 10, the optical transmission device 5 according to the second embodiment includes a 16: 2 multiplexer 316, a 2: 1 multiplexer 302, a first selector 307, a second selector 308, and a first selector 307. The configuration includes an LN modulator driver 311, a second LN modulator driver 312, a laser diode 315, a modulation unit 317, and a control unit 350.

  The 16: 2 multiplexer 316 multiplexes 16 electric signals having a bit rate of 2.5 Gbps input from the outside every eight, and generates two signals D1 and D2 having a bit rate of 20 Gbps.

  The 16: 2 multiplexer 316 outputs the signal D1 to the first selector 307 and the 2: 1 multiplexer 302, and outputs the signal D2 to the second selector 308 and the 2: 1 multiplexer 302.

  The 2: 1 multiplexer 302 multiplexes the two signals D1 and D2 output from the 16: 2 multiplexer to generate a signal D having a bit rate of 40 Gbps, and outputs the generated signal D to the first selector 307.

  The first selector 307 selects either the signal D output from the 2: 1 multiplexer 302 or the signal D1 output from the 16: 2 multiplexer 316 according to the first control signal output from the control unit 350. Then, the selected signal is output to the first LN modulator driver 311.

  The second selector 308 selects either the signal D2 output from the 16: 2 multiplexer 316 or the constant voltage DC according to the second control signal output from the control unit 350, and selects the selected signal as the second signal. To the LN modulator driver 312.

  The first LN modulator driver 311 amplifies the signal output from the first selector 307 to a necessary amplitude by 0-π modulation, and uses a modulator 317 (first Mach-Zehnder type modulation described later) as a drive signal. Output to the device 313).

  The second LN modulator driver 312 amplifies the signal output from the second selector 308 to a necessary amplitude by 0-π modulation, and uses a modulator 317 (second Mach-Zehnder type modulation described later) as a drive signal. Output to the device 314).

  The laser diode 315 is a light source that generates an optical carrier wave used as a carrier wave, and the output light of the laser diode 215 is supplied to the modulation unit 317.

  The modulation unit 317 includes a first arm 331, a second arm 332, a branching unit 321, a first Mach-Zehnder type modulator 313, a second Mach-Zehnder type modulator 314, a phase shift unit 318, and an optical signal. A synthesis unit 322 is provided.

  The first arm 331 and the second arm 332 are set to have the same optical path length.

  The branching unit 321 branches the optical carrier wave output from the laser diode 315 and outputs the optical carrier wave with the same intensity to the first arm 331 and the second arm 332.

  The first arm 331 includes a first Mach-Zehnder type modulator 313, and the second arm 332 includes a second Mach-Zehnder type modulator 314 and a phase shift unit 318, and the second Mach-Zehnder type A phase shift unit 318 is disposed after the modulator 214.

  The first Mach-Zehnder type modulator 313 receives the drive signal output from the first LN modulator driver 311, and the second Mach-Zehnder type modulator 314 receives the second LN modulator driver 312. The drive signal output from is input. The second Mach-Zehnder modulator 314 receives an LN bias from the control unit 250 for adjusting the transmittance.

  The phase shift unit 318 changes the phase shift amount of the optical signal transmitted by the second arm 332 according to the value of the bias A output from the control unit 350.

  The optical signal combining unit 322 combines the optical signals output from the first arm 331 and the second arm 332, and outputs the combined optical signal as a transmission signal.

  The modulation unit 317 outputs modulated light by changing the phase of the optical carrier according to the drive signals output from the first LN modulator driver 311 and the second LN modulator driver 312.

  The control unit 350 controls the selection operation of the first selector 307 and the second selector 308, the transmittance of the second Mach-Zehnder type modulator 314, and the phase shift amount of the optical signal by the phase shift unit 318.

  Next, the configuration of the optical receiver 6 according to the second embodiment will be described.

  As shown in FIGS. 11 and 12, the optical receiver 6 of the second embodiment adds a 2:16 demultiplexer 248 to the optical receiver 2 (FIG. 7) of the first embodiment described above. This is the configuration.

  The 2:16 demultiplexer 248 receives the output signal of the first selector 245 and the output signal of the second selector 246, and separates the two input signals into eight 2.5 Gbps signals. Output. That is, the 2:16 demultiplexer 248 outputs a total of 16 2.5 Gbps signals. Other configurations of the optical receiver 6 are the same as those of the optical receiver 2 of the first embodiment.

  Next, an operation when the optical transmission apparatus 5 according to the second embodiment uses the DQPSK modulation method will be described with reference to FIG.

  When transmitting a DQPSK signal from the optical transmission apparatus 5 of the second embodiment, the first selector 307 selects the signal D1, and the second selector 308 selects the signal D2.

  The first LN modulator driver 311 amplifies the signal D1 to a necessary amplitude by 0-π modulation. The second LN modulator driver 312 amplifies the signal D2 to a necessary amplitude by 0-π modulation.

  In general, in the Mach-Zehnder type modulator, the voltage Vπ required to shift the phase of the optical signal by π in one modulator is about 3.5V to 6V. By supplying a voltage having an amplitude, that is, about 7 Vpp to 12 Vpp, 0-π modulation is possible, and a DQPSK signal having a binary phase can be generated.

  The phase shift unit 318 included in the second arm 332 sets the phase shift amount of the optical signal transmitted by the second arm 332 to π / 2 according to the second control voltage output from the control unit 350.

  The optical signal combining unit 322 combines the optical signals output from the first arm 331 and the second arm 332, and outputs the combined optical signal as a transmission signal.

  As a result, a DQPSK signal having a sample rate of 20 Gsps, a bit rate of 40 Gbps, and a quaternary phase as shown by a constellation 226 in FIG. 9 is generated, and the optical transmission device 5 outputs the DQPSK signal as a transmission signal.

  A differential drive type may be used for the Mach-Zehnder type modulator. In that case, the first Mach-Zehnder type modulator 313 and the second Mach-Zehnder type modulator 314 may be supplied with a differential signal having an amplitude of 2Vπ as a drive signal.

  Next, the operation when the DPSK modulation method of the optical transmission apparatus 5 according to the second embodiment is used will be described with reference to FIG.

  When transmitting a DPSK signal from the optical transmission device 5 of the second embodiment, the first selector 307 selects the signal D output from the 2: 1 multiplexer 302 and having a bit rate of 40 Gbps, The selector 308 selects the constant voltage DC.

  The first LN modulator driver 311 amplifies the signal D to the required amplitude 2Vπ by 0-π modulation.

  When the constant voltage DC is output from the second selector 308, the output amplitude of the second LN modulator driver 312 is zero. In addition, the control unit 350 sets the value of the LN bias supplied to the modulation unit 317 so that the transmittance of the second Mach-Zehnder type modulator 314 becomes zero.

  In this case, since the second Mach-Zehnder type modulator 314 blocks the optical carrier wave of the laser diode 315, the phase modulated by the first Mach-Zehnder type modulator 313 and having a binary phase is modulated from the modulation unit 317. Only the signal is output. That is, the optical transmission device 5 illustrated in FIG. 10 outputs a DPSK signal having a binary phase indicated by a constellation 225 as a transmission signal.

  Next, the operation when the optical receiver 6 of the second embodiment uses the DQPSK modulation method will be described with reference to FIG.

  When the optical receiver 6 receives a DQPSK signal with a bit rate = 40 Gbps, the sample rate is 20 Gsps and the symbol interval is 50 ps. The DQPSK signal (optical signal) received by the optical receiver 6 is input to the optical splitter 240.

  The optical splitter 240 branches the received optical signal and outputs it to the first delay interferometer 241 and the second delay interferometer 242.

  The first delay interferometer 241 branches the input optical signal and outputs it to the first arm 251 and the second arm 252.

  The optical transmission path 256 provided in the first arm 251 transmits the optical signal transmitted by the first arm 251 to the optical signal transmitted by the second arm 252 at a time T = 2τ = 2 / B = 50 ps. Just delay. That is, the second arm 252 is set to have an optical path length shorter than the first arm 251 by a length corresponding to 2 / B because the first arm 251 includes the optical transmission path 256.

  The phase shift unit 255 provided in the second arm 252 sets the phase shift amount of the optical signal transmitted by the second arm 252 to π / 4 according to the first control voltage output from the control unit 280.

  The directional coupler 253 combines the optical signal output from the first arm 252 and the optical signal output from the second arm 252, and further separates and outputs the two signals having a phase difference of π. . At this time, in the directional coupler 253, an optical signal output from the second arm 252 is shifted in phase by π / 4, the bit rate is B / 2 sps, and the phase is quaternary. One symbol = 50 ps before the optical signal output from the arm 251 interferes. As a result, the directional coupler 253 outputs a differential optical signal with a bit rate of B / 2 having a binary light intensity corresponding to the phase difference between the two input optical signals.

  For example, a balanced PD (Photo Detector) is used for the first balanced photoelectric signal converter 243. The first balanced optical-electrical signal converter 243 converts the differential optical signal output from the first delay interferometer 241 into an electrical signal and outputs it to the 1: 2 demultiplexer 247 and the first selector 245. To do.

  The 1: 2 demultiplexer 247 separates the signal output from the first balanced optical-electrical signal converter 243 for each bit, and generates two signals with a bit rate of B / 2, one of which is the first 1 is output to the selector 245 and the other is output to the second selector 246.

  The first selector 245 includes a first balanced optical-electrical signal converter out of the signal output from the first balanced optical-electrical signal converter 243 and the signal output from the 1: 2 demultiplexer 247. A signal with a bit rate of B / 2 output from 243 is selected and output to the 2:16 demultiplexer 248.

  On the other hand, the second delay interferometer 242 branches the input optical signal and outputs it to the first arm 261 and the second arm 262.

  The optical transmission path 266 included in the first arm 261 is configured to transmit the optical signal transmitted by the first arm 261 to the optical signal transmitted by the second arm 262 at a time T = 2τ = 2 / B = 50 ps. Just delay.

  The phase shift unit 265 included in the second arm 262 sets the phase shift amount of the optical signal transmitted by the second arm 262 to −π / 4 according to the second control voltage output from the control unit 280.

  The directional coupler 263 combines the optical signal output from the first arm 262 and the optical signal output from the second arm 262, and further separates and outputs the two signals having a phase difference of π. . At this time, in the directional coupler 263, the optical signal output from the second arm 262 is shifted in phase by −π / 4, the bit rate is B / 2 sps, and the phase is quaternary. 1 symbol = 50 ps before the optical signal output from the arm 261 interferes. As a result, the directional coupler 263 outputs a differential optical signal with a bit rate of B / 2 having a binary light intensity corresponding to the phase difference between the two input optical signals.

  The second balanced optical-electrical signal converter 244 converts the differential optical signal output from the second delay interferometer 242 into an electrical signal and outputs it to the second selector 246.

  The second selector 246 includes a second balanced optical-electrical signal converter out of the signal output from the second balanced optical-electrical signal converter 244 and the signal output from the 1: 2 demultiplexer 247. A signal having a bit rate of B / 2 output from 244 is selected and output to the 2:16 demultiplexer 248.

  The 2:16 demultiplexer 248 separates the 20 Gbps signals output from the first selector 245 and the second selector 246 into eight signals of 2.5 Gbps, respectively, and outputs the signals.

  Next, the operation when the optical receiver 6 of the second embodiment uses the DPSK modulation method will be described with reference to FIG.

  When the optical receiver 6 receives a DPSK signal with a bit rate = 40 Gbps, the DPSK signal is a binary signal, so that 1 symbol interval = 1 bit interval = 25 ps. The DPSK signal (optical signal) received by the optical receiver 6 is input to the optical splitter 240 in the same manner as the DQPSK signal.

  The optical splitter 240 branches the received optical signal and outputs it to the first delay interferometer 241 and the second delay interferometer 242.

  The first delay interferometer 241 branches the input optical signal and outputs it to the first arm 251 and the second arm 252.

  The optical transmission path 256 provided in the first arm 251 transmits the optical signal transmitted by the first arm 251 to the optical signal transmitted by the second arm 252 at a time T = 2τ = 2 / B = 50 ps. Just delay.

  The phase shift unit 255 provided in the second arm 252 sets the phase shift amount of the optical signal transmitted by the second arm 252 to 0 according to the first control voltage output from the control unit 280.

  Note that when the DPSK modulation method is used, an optical signal is also input to the second delay interferometer 242, but its output is not selected by the second selector 246. That is, when the DPSK modulation method is used, the optical receiver 6 does not use the second delay interferometer 242.

  When the DPSK modulation method is used, the sample rate of the received DPSK signal is the same as the bit rate B of the received signal.

  The directional coupler 253 combines the optical signal output from the first arm 252 and the optical signal output from the second arm 252, and further separates and outputs the two signals having a phase difference of π. . At this time, in the directional coupler 253, an optical signal having a bit rate of B and a phase of four values output from the second arm 252 and one symbol output from the first arm 251 = 50 ps before. Interfere with other optical signals. As a result, the directional coupler 253 outputs a differential optical signal with a bit rate of B having a binary light intensity corresponding to the phase difference between the two input optical signals.

  The first balanced optical-electrical signal converter 243 converts the differential optical signal output from the first delay interferometer 241 into an electrical signal and outputs it to the 1: 2 demultiplexer 247 and the first selector 245. To do.

  The 1: 2 demultiplexer 247 separates the signal output from the first balanced optical-electrical signal converter 243 for each bit, and generates two signals with a bit rate of B / 2, one of which is the first 1 is output to the selector 245 and the other is output to the second selector 246.

  The first selector 245 is a signal output from the 1: 2 demultiplexer 247 out of the signal output from the first balanced photoelectric signal converter 243 and the signal output from the 1: 2 demultiplexer 247. Is output to the 2:16 demultiplexer 248. The second selector 246 selects the signal output from the 1: 2 demultiplexer 247 and outputs the selected signal to the 2:16 demultiplexer 248.

  The 2:16 demultiplexer 248 separates the two signals output from the 1: 2 demultiplexer 247 into eight 2.5 Gbps signals, respectively, and outputs a total of 16 2.5 Gbps signals.

  Also in the optical transmission device 5, the optical reception device 6, and the optical communication system of the second embodiment, the same effects as the optical transmission device 1, the optical reception device 2, and the optical communication system 3 of the first embodiment are obtained. It is done.

(Third embodiment)
FIG. 13 is a block diagram illustrating a configuration example of the optical transmission apparatus according to the third embodiment, and FIG. 14 is a block diagram illustrating a configuration example of the optical reception apparatus according to the third embodiment. Since the configuration and operation of the optical communication system are the same as those of the optical communication system according to the first embodiment, description thereof is omitted.

  As illustrated in FIG. 13, the optical transmission device 7 according to the third embodiment outputs the signal Db output from the 2: 1 multiplexer 302 to the second selector 308. This is different from the transmission device 5 (FIGS. 9 and 10). Other configurations of the optical transmission device 7 are the same as those of the optical transmission device 5 of the second embodiment.

  As shown in FIG. 14, the optical receiver 8 of the third embodiment includes an output signal of the first balanced optical-electrical signal converter 243 and a second balanced optical-electrical signal converter 244. This is different from the optical receiver 6 (FIGS. 11 and 12) of the second embodiment in that a difference signal from the output signal is input to a 1: 2 demultiplexer 247.

  In other words, the optical receiver 8 of the third embodiment outputs the difference between the output signal of the first balanced optical-electric signal converter 243 and the output signal of the second balanced optical-electric signal converter 244. The difference detector 360 is provided.

  For example, the difference detector 360 subtracts the difference signal obtained by subtracting the output value of the second balanced optical-electrical signal converter 244 from the output value of the first balanced optical-electrical signal converter 243 from the 1: 2 demultiplexer 247. Output to. Other configurations and operations of the optical receiver 8 are the same as those of the optical receiver 6 of the second embodiment.

  The optical transmission device 7 and the optical reception device 8 of the third embodiment have the same transmission operation and reception operation when using the DQPSK modulation method as those of the second embodiment described above, and use the DPSK modulation method. Only the operation is different from that of the second embodiment. Hereinafter, only the operation when the DPSK modulation method is used will be described, and the description of the operation when the DQPSK modulation method is used will be omitted.

  In the present embodiment, the case where the bit rate B of the transmission signal and the reception signal is 40 Gbps and τ = 1 / B = 25 ps will be described as an example.

  First, the operation when the optical transmitter 7 of the third embodiment transmits a DPSK signal will be described with reference to FIG.

  When the DPSK signal is transmitted, the signal D output from the 2: 1 multiplexer 302 is input to the first selector 307 and the signal Db is input to the second selector 308.

  The first selector 307 selects the signal D according to the first control signal output from the control unit 350 and outputs the selected signal D to the first LN modulator driver 311.

  The second selector 308 selects the signal Db according to the second control signal output from the control unit 350, and outputs the selected signal Db to the second LN modulator driver 312.

  The first LN modulator driver 311 amplifies the amplitude of the signal D to 2Vπ and outputs the amplified signal to the first Mach-Zehnder type modulator 313 as a drive signal. This causes the first Mach-Zehnder type modulator 313 to perform 0-π modulation.

  The second LN modulator driver 312 amplifies the amplitude of the signal Db to 2Vπ and outputs the amplified signal to the Mach-Zehnder type modulator 314 as a drive signal. This causes the second Mach-Zehnder modulator 314 to perform 0-π modulation.

  Here, since the first Mach-Zehnder type modulator 313 and the second Mach-Zehnder type modulator 314 are driven with signals inverted from each other, the phase of the modulated optical signal is shifted by π. It becomes.

  However, in this embodiment, the phase shift amount of the optical signal is set to π by the phase shift unit 318 provided in the second arm 332 of the modulation unit 317. As a result, the optical signal output from the second Mach-Zehnder type modulator 314 is in phase with the optical signal output from the first Mach-Zehnder type modulator 313.

  Therefore, the optical signal (DPSK signal) output from the optical signal combining unit 322 of the modulation unit 317 is the light output from the optical transmission device 5 of the second embodiment, as indicated by the constellation 330 in FIG. It is twice as strong as the signal.

  In the optical transmission device 5 according to the second embodiment, when the DPSK modulation method is used, the transmittance of the second Mach-Zehnder modulator 314 included in the modulation unit 317 is set to 0. The optical signal input to the Zehnder type modulator 314 is wasted.

  In the optical transmission device 7 of the third embodiment, the output signal of the light source (laser diode 315) can be used without waste even when operating in the DPSK modulation method. A transmission signal having twice the intensity can be obtained.

  Next, the operation when the optical receiver 8 of the third embodiment receives a DPSK signal will be described with reference to FIG.

  When a DPSK signal having a bit rate of 40 Gbps is received by the optical receiver 8 of the present embodiment, since the symbol rate is equal to the bit rate, the first delay interferometer 241 and the second delay interferometer 242 each have 50 ps = Interfering with the signal 2 bits before.

  In the first delay interferometer 241 of this embodiment, the phase shift amount of the optical signal by the phase shift unit 255 is set to 0, and in the second delay interferometer 242, the phase shift amount of the optical signal by the phase shift unit 265 is set. Is set to π. As a result, the first delay interferometer 241 and the second delay interferometer 242 output signals whose logics are inverted at the same speed (40 Gbps) as the bit rate. A difference signal between the two signals is supplied to the 1: 2 demultiplexer 247. In the present embodiment, an example in which the difference detector 360 is used is shown, but a configuration without the difference detector 360 is also possible. In that case, the differential input type 1: 2 demultiplexer 247 is used, and the first delay interferometer 241 and the second delay interferometer 242 output the positive and negative inputs of the 1: 2 demultiplexer 247, respectively. The signals may be supplied at the same timing.

  The operations of the first selector 245, the second selector 246, and the 2:16 demultiplexer 248 are the same as those in the second embodiment described above.

  In the optical receiver 6 according to the second embodiment, the optical signal input to the second delay interferometer 242 is not used during operation using the DPSK modulation method, and thus the optical receiver 6 is input to the second delay interferometer 242. The optical signal component is wasted. In the optical receiver 8 of the third embodiment, the received signal can be used without waste even when operating in the DPSK modulation method.

  According to the optical transmission device 7, the optical reception device 8, and the optical communication system of the third embodiment, the same effects as those of the optical transmission device 5, the optical reception device 6, and the optical communication system of the second embodiment are obtained. At the same time, a DPSK signal twice as strong as that of the optical transmitter 5 of the second embodiment is obtained from the optical transmitter 7. Further, in the reception operation using the DPSK modulation method by the optical receiver 8, the optical signal input to the second delay interferometer 242 is also used, so that the received signal can be used without waste.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  This application claims the priority on the basis of Japanese Patent Application No. 2008-250363 for which it applied on September 29, 2008, and takes in those the indications of all here.

Claims (10)

When the bit rate of the optical signal to be transmitted is B,
A first selector that selects and outputs a first signal having a bit rate of B or a second signal having a bit rate of B / 2;
A second selector that selects and outputs a third signal having a bit rate of B, a fourth signal having a bit rate of B / 2, or a fifth signal having a constant voltage;
A light source that generates an optical carrier;
First and second Mach-Zehnder type modulators for branching the optical carrier wave, modulating the branched optical carrier wave and outputting the modulated carrier wave;
A phase shift unit that shifts the phase of the optical signal output from the second Mach-Zehnder modulator;
A first modulation driver that drives the first Mach-Zehnder modulator according to a signal output from the first selector;
A second modulation driver that drives the second Mach-Zehnder modulator according to a signal output from the second selector;
An optical signal combining unit that combines an optical signal output from the first Mach-Zehnder modulator and an optical signal output from the phase shift unit, and outputs the optical signal as the transmission signal;
A controller that controls the first selector, the second selector, the second Mach-Zehnder modulator, and the phase shift unit;
Have
The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Causing the first selector to select the first signal, causing the second selector to select the third or fifth signal,
When transmitting an optical signal modulated by the DQPSK modulation method,
An optical transmission apparatus that causes the first selector to select the second signal and causes the second selector to select the fourth signal. The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Causing the second selector to select the third signal, setting the phase shift amount by the phase shift unit to π,
When transmitting an optical signal modulated by the DQPSK modulation method,
The optical transmission device according to claim 1, wherein a phase shift amount by the phase shift unit is set to π / 2. The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Causing the second selector to select the fifth signal;
2. The optical transmission device according to claim 1, wherein a required bias voltage is supplied to the second Mach-Zehnder type modulator so that an optical signal transmittance of the second Mach-Zehnder type modulator becomes zero. When the bit rate of the optical signal to be transmitted is B,
A first selector that selects and outputs a first signal having a bit rate of B or a second signal having a bit rate of B / 2;
A second selector for selecting and outputting a fourth signal having a bit rate of B / 2 or a fifth signal having a constant voltage;
A light source that generates an optical carrier;
First and second Mach-Zehnder type modulators for branching the optical carrier wave, modulating the branched optical carrier wave and outputting the modulated carrier wave;
A phase shift unit that shifts the phase of the optical signal output from the second Mach-Zehnder modulator;
A first modulation driver that drives the first Mach-Zehnder modulator according to a signal output from the first selector;
A second modulation driver that drives the second Mach-Zehnder modulator according to a signal output from the second selector;
An optical signal combining unit that combines an optical signal output from the first Mach-Zehnder modulator and an optical signal output from the phase shift unit, and outputs the optical signal as the transmission signal;
A controller that controls the first selector, the second selector, the second Mach-Zehnder modulator, and the phase shift unit;
Have
The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Causing the first selector to select the first signal, causing the second selector to select the fifth signal,
When transmitting an optical signal modulated by the DQPSK modulation method,
An optical transmission apparatus that causes the first selector to select the second signal and causes the second selector to select the fourth signal. The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Supplying a required bias voltage to the second Mach-Zehnder type modulator so that the optical signal transmittance of the second Mach-Zehnder type modulator becomes 0;
When transmitting an optical signal modulated by the DQPSK modulation method,
The optical transmission device according to claim 4, wherein a phase shift amount by the phase shift unit is set to π / 2. When the bit rate of the optical signal to be transmitted is B,
A first selector that selects and outputs a first signal having a bit rate of B or a second signal having a bit rate of B / 2;
A second selector for selecting and outputting a third signal having a bit rate of B or a fourth signal having a bit rate of B / 2;
A light source that generates an optical carrier;
First and second Mach-Zehnder type modulators for branching the optical carrier wave, modulating the branched optical carrier wave and outputting the modulated carrier wave;
A phase shift unit that shifts the phase of the optical signal output from the second Mach-Zehnder modulator;
A first modulation driver that drives the first Mach-Zehnder modulator according to a signal output from the first selector;
A second modulation driver that drives the second Mach-Zehnder modulator according to a signal output from the second selector;
An optical signal combining unit that combines an optical signal output from the first Mach-Zehnder modulator and an optical signal output from the phase shift unit, and outputs the optical signal as the transmission signal;
A controller that controls the first selector, the second selector, the second Mach-Zehnder modulator, and the phase shift unit;
Have
The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Causing the first selector to select the first signal, causing the second selector to select the third signal,
When transmitting an optical signal modulated by the DQPSK modulation method,
An optical transmission apparatus that causes the first selector to select the second signal and causes the second selector to select the fourth signal. The controller is
When transmitting an optical signal modulated by the DPSK modulation method,
Set the phase shift amount by the phase shift unit to π,
When transmitting an optical signal modulated by the DQPSK modulation method,
The optical transmission device according to claim 6, wherein a phase shift amount by the phase shift unit is set to π / 2.   A 2: 1 multiplexer for multiplexing the second signal and the fourth signal to generate the first signal and generating the third signal that is an inverted signal of the first signal; The optical transmission device according to claim 1, comprising: an optical transmission device according to claim 1; When the bit rate of the received optical signal is B,
An optical splitter for branching the received optical signal into two;
The first arm, the second arm shorter than the first arm by a length corresponding to 2 / B, and the second arm to which the input optical signal is further branched and input An optical signal having a binary optical intensity corresponding to the phase of the optical signal, the optical signal branched by the optical splitter. A first delay interferometer that converts to
The third arm to which the input optical signal is further branched and input, the fourth arm whose optical path length is shorter than the third arm by a length corresponding to 2 / B, and the fourth arm A second phase shift unit that shifts the phase of the transmitted optical signal, and converts the other optical signal branched by the optical splitter into an optical signal having a binary light intensity corresponding to the phase of the optical signal. A second delay interferometer to convert;
A first optical-electrical signal converter that converts an optical signal output from the first delay interferometer into an electrical signal;
A second optical-electrical signal converter that converts an optical signal output from the second delay interferometer into an electrical signal;
A control unit for controlling the first phase shift unit and the second phase shift unit;
Have
The controller is
When receiving an optical signal modulated by the DPSK modulation method,
A phase shift amount by the first phase shift unit is set to 0;
When receiving an optical signal modulated by the DQPSK modulation method,
An optical receiver that sets a phase shift amount by the first phase shift unit to + π / 4 and sets a phase shift amount by the second phase shift unit to −π / 4. An optical transmitter according to any one of claims 1 to 3 ,
An optical receiver according to claim 9 ,
An optical communication system.

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