JP2015162723A - Optical transmitter, optical receiver, optical transmission method, and optical reception method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmitter capable of transmitting a plurality of signal beams with a single unit and to provide an optical receiver.SOLUTION: The optical transmitter includes: frequency converting means for converting frequency bands of a plurality of electric signals to frequency bands that are not mutually overlapped for each electric signal and outputting converted electric signals; multiplexing means for frequency division multiplexing the converted electric signals and outputting the frequency division multiplexed electric signals; and an optical modulator for modulating an optical carrier wave with the frequency division multiplexed electric signals and outputting signal beams.

Description

  The present invention relates to an optical transmitter, an optical receiver, an optical transmission method, and an optical reception method, and in particular, an optical transmitter, an optical receiver, an optical transmission method, and an optical device that are used in an optical transmission system employing a digital coherent transmission method. It relates to the receiving method.

  With the recent increase in demand for data communication services, the introduction of a large-capacity optical fiber transmission system that employs a digital coherent transmission method and that multiplexes wavelengths with high density is in progress. In addition, a polarization multiplexing optical transmission system in which signal light is multiplexed by polarized waves with orthogonal carrier waves has been developed.

  For example, Patent Document 1 describes a configuration of a coherent optical receiver having a chromatic dispersion compensation function. Patent Document 2 describes a configuration example of a polarization multiplexed optical transmission system.

JP2013-081066A (paragraph [0022]-[0036]) JP 2012-119759 A ([0024]-[0025] paragraphs)

  An optical transmitter used in a general wavelength multiplexing transmission system modulates and outputs an optical carrier wave having a single wavelength. Then, the optical multiplexers combine the signal lights having different wavelengths output from the plurality of optical transmitters, and send them to the transmission line as wavelength multiplexed signal light. Further, in a general wavelength multiplexing transmission system, signal light is separated for each wavelength by an optical demultiplexer that separates signal light including light of different wavelengths for each wavelength. The separated signal light is received by different optical receivers for each wavelength.

However, in such a wavelength division multiplexing transmission system, one optical transmitter and an optical receiver are required for each wavelength, so that the efficiency of accommodating the wavelength of the signal light per optical transmitter and optical receiver is low. However, there is a problem that it is difficult to reduce the size and price of the optical transmission system. In addition, since an optical multiplexer and an optical demultiplexer are necessary for multiplexing and demultiplexing wavelengths, there is a problem that the transmission distance may be limited due to the loss of the optical multiplexer and the optical demultiplexer. Patent Documents 1 and 2 do not present a technique for solving these problems caused by low accommodation efficiency of the number of wavelengths per optical transmitter or optical receiver.
(Object of invention)
An object of the present invention is to provide an optical transmitter, an optical receiver, an optical transmission method, and an optical reception method capable of transmitting a plurality of signal lights by one unit.

  The optical transmitter of the present invention converts frequency bands of a plurality of electrical signals into frequency bands that do not overlap each other for each electrical signal, and outputs the converted electrical signal, and the converted A multiplexing means for frequency-multiplexing the electrical signal and outputting the frequency-multiplexed electrical signal; and an optical modulator for modulating an optical carrier wave by the frequency-multiplexed electrical signal and outputting signal light. Prepare.

  The optical receiver of the present invention receives a signal light that is wavelength-multiplexed with optical carriers having different wavelengths that are phase-modulated by different electrical signals, and mixes the signal light with local light to detect the detected signal. Detection means for outputting, and frequency conversion means for extracting and outputting a received signal for each frequency band in which each of the electrical signals is included from the detected signal.

  The optical transmission method of the present invention converts a frequency band of a plurality of electrical signals into a frequency band that does not overlap each other for each electrical signal, outputs the converted electrical signal, and converts the converted electrical signal Frequency-multiplexed, the frequency-multiplexed electrical signal is output, an optical carrier is modulated by the frequency-multiplexed electrical signal, and signal light is output.

  In the optical receiving method of the present invention, an electric signal detected by mixing signal light with local light, which is inputted with signal light that is wavelength-multiplexed with optical carriers having different wavelengths and phase-modulated by different electric signals, respectively. The received signal is extracted for each frequency band including each of the transmission signals from the detected electrical signal and output.

  The optical transmitter, the optical receiver, the optical transmission method, and the optical reception method of the present invention are advantageous in that the optical transmitter and the optical receiver can be reduced in size and price, and the transmission distance of the optical transmission system can be increased. Play.

It is a block diagram which shows the structure of the optical transmitter of 1st Embodiment. It is a figure which shows the spectrum of the signal in an optical transmitter. It is a figure which shows the example of the wavelength spectrum and polarization of signal light. It is a block diagram which shows the structure of the optical receiver of 2nd Embodiment. It is a figure which shows the example of the wavelength spectrum and polarization of signal light. It is a figure which shows the frequency spectrum of the signal in an optical receiver. It is a block diagram which shows the structure of the optical receiver of 3rd Embodiment. It is a block diagram which shows the structure of the fixed equalization circuit of 3rd Embodiment. It is a figure which shows the frequency spectrum of the signal in each part of an optical receiver. It is a block diagram which shows the structure of the optical transmission system of 4th Embodiment. It is a block diagram which shows the structure of the optical transmitter of 5th Embodiment. It is a block diagram which shows the structure of the optical receiver of 6th Embodiment.

  In the following embodiments, an optical transmitter and an optical receiver that are mainly used in an optical transmission system using a digital coherent reception method will be described. In each embodiment, an optical transmitter capable of wavelength-multiplexing and transmitting two signal lights by one unit, or an optical receiver capable of receiving wavelength-multiplexed signal light by one unit will be described.

(First embodiment)
FIG. 1 is a block diagram illustrating a configuration of an optical transmitter 11 according to the first embodiment of this invention. The optical transmitter 11 includes encoding circuits 32 and 33, frequency conversion circuits 52 and 53, multiplexing circuits 71a to 71d, DA (digital to analog) conversion circuits 81a to 81d, a polarization multiplexing modulator 51, and a local light source 110. . The optical transmitter 11 may further include a CPU (central processing unit) 95 and a memory 96. The memory 96 is a semiconductor nonvolatile memory, for example, and stores a program for operating the CPU 95.

  The transmission signals 22 and 23 are both electrical signals having a transmission rate of 100 Gbps. The transmission signal 22 is converted by the encoding circuit 32 into four-lane modulated signals 42a to 42d corresponding to a polarization multiplexing QPSK (quadrature phase shift keying) modulation method. The transmission signal 23 is converted by the encoding circuit 33 into 4-lane modulation signals 43a-43d corresponding to a polarization multiplexing 16QAM (quadrature amplitude modulation) modulation method.

  The frequency conversion circuits 52 and 53 frequency-convert the modulated signals 42a-42d and 43a-43d and adjust the spectrum of the frequency-converted modulated signal. Multiplex circuits 71a-71d are digital adder circuits that add the modulated signals 62a and 63a, 62b and 63b, 62c and 63c, and 62d and 63d output from the frequency conversion circuits 52 and 53, respectively, on the frequency axis. Multiplex with. The DA conversion circuits 81 a to 81 d convert the signals multiplexed by the multiplexing circuits 71 a to 71 d into modulation signals 91 a to 91 d that are analog signals suitable for modulation by the polarization multiplexing modulator 51. The frequency conversion circuits 52 and 53 perform frequency conversion of each modulation signal so that the frequency band of the modulation signals 62a to 62d and the frequency band of the modulation signals 63a to 63d do not overlap.

  The polarization multiplexing modulator 51 modulates the local light 120 output from the local light source 110 by the modulation signals 91a to 91d. The local light 120 becomes an optical carrier wave of the signal lights 24 and 25. The polarization multiplexing modulator 51 generates wavelength multiplexed signal lights 24 and 25 including the transmission signals 22 and 23 and outputs them to the optical transmission line.

  FIG. 2 is a diagram illustrating a spectrum of a signal in the optical transmitter 11. Each vertical axis in FIG. 2 indicates the amplitude of the signal. Since all of the modulation signals 42a-42d, 43a-43d, 62a-62d, 63a-63d, 91a-91d are digitized, (a)-(e) in FIG. The virtual frequency spectrum when it is assumed that it converted into the analog signal by is shown. FIG. 2A shows the frequency spectrum of the modulated signals 42a-42d. FIG. 2B shows the frequency spectrum of the modulation signals 43a-43d.

  The modulated signals 42a, 42b, 42c, and 42d are respectively the X-polarized I (inphase) axis, the X-polarized Q (quadrature) axis, and the Y-polarized wave when the transmission signal 22 is subjected to polarization multiplexing QPSK modulation. It is a signal corresponding to the Q axis of IY polarization. The X polarization and the Y polarization correspond to optical carriers (carriers) orthogonal to each other in the polarization multiplexing modulator 51 described later. The baud rates of the modulated signals 42a-42d are all 25 Gbaud. Each of the pair of modulation signals 42a and 42b and the pair of modulation signals 42c and 42d transmits 2-bit information with one symbol. These modulated signals 42a, 42b, 42c, and 42d are digitized with a sampling rate of 100 Gsample / s (4 samples per symbol) and a bit resolution of 8 bits. The center frequencies of the frequency spectra of the modulation signals 42a, 42b, 42c, and 42d are all zero, and the occupied frequency band is 50 GHz.

  On the other hand, the modulation signals 43a, 43b, 43c, and 43d are respectively the X polarization I axis, the X polarization Q axis, the Y polarization I axis, and the Y when the transmission signal 23 is subjected to polarization multiplexing 16QAM modulation. It is a signal corresponding to the Q axis of polarization. The baud rates of modulated signals 43a-43d are all 12.5 Gbaud, and the pair of modulated signals 43a and 43b and the pair of modulated signals 43c and 43d each transmit 4 bits of information with one symbol. These modulated signals 43a, 43b, 43c, and 43d are digitized at a sampling rate of 100 Gsample / s (8 samples per symbol) and a bit resolution of 8 bits. The frequency spectrum of the modulation signals 43a, 43b, 43c, and 43d has a center frequency of zero and an occupied frequency band of 25 GHz.

  The modulation signals 42a-42d (FIG. 2A) are modulated signals 62a-62d (FIG. 2), which are frequency-shifted by the frequency conversion circuit 52 and have side lobes other than the main spectrum removed and frequency shifted by -12.5 GHz. (C)). Similarly, the modulation signals 43a-43d (FIG. 2B) are modulated signals 63a-63d (FIG. 2) whose side lobes other than the main spectrum are removed by the frequency conversion circuit 53 and whose frequency is shifted by +25 GHz. (D)). The modulation signals 62a-62d and the modulation signals 63a-63d are multiplexed by the multiplexing circuits 71a-71d ((e) in FIG. 2) and converted to the modulation signals 91a-91d by the DA conversion circuits 81a-81d. Modulation signals 91a-91d are analog signals.

  As shown in FIG. 2E, the modulation signals 62a-62d and the modulation signals 63a-63d are frequency-multiplexed in the modulation signals 91a-91d output from the DA conversion circuits 81a-81d. The frequency interval between the modulation signals 62a-62d and the modulation signals 63a-63d is 37.5 GHz. The modulation signals 91a, 91b, 91c, and 91d are respectively the X-polarization I-axis modulation port, the X-polarization Q-axis modulation port, the Y-polarization I-axis modulation port, and the Y-polarization of the polarization multiplexing modulator 51. To the Q-axis modulation port.

  FIG. 3 is a diagram illustrating an example of the wavelength spectrum and polarization of the signal lights 24 and 25. The “X polarization component” and “Y polarization component” in FIG. 3 both indicate the amplitude of the signal light. Due to the above-described function of the optical transmitter 11, the signal light 24 and the signal light 25 are wavelength-multiplexed and output to the signal light output from the polarization multiplexing modulator 51. Since the frequency interval between the modulation signals 62a-62d and the modulation signals 63a-63d is 37.5 GHz, as shown in FIG. 3, the wavelength interval between the signal light 24 and the signal light 25 is about 1550 nm as the wavelength of the carrier wave. In this case, it is about 0.3 nm. The signal light 24 transmits the transmission signal 22 by polarization multiplexing QPSK modulation, and the signal light 25 transmits the transmission signal 23 by polarization multiplexing 16 QAM modulation.

  The general operations of the encoding circuits 32 and 33, the local light source 110, the DA conversion circuits 81a to 81d, and the polarization multiplexing modulator 51 for generating the polarization multiplexed signal light described above are well known. Yes. For this reason, the detailed description regarding these components is abbreviate | omitted.

  In the recommendation of ITU-T (International Telecommunication Union Telecommunication Standardization Sector), a wavelength interval (wavelength grid) in wavelength multiplexing transmission is defined. For example, the wavelength of the local light 120 of the optical transmitter 11 may be set to an intermediate wavelength between the wavelengths defined as the wavelength grid in the ITU-T recommendation.

  As described above, the optical transmitter 11 according to the first embodiment generates modulated signals 91a to 91d obtained by frequency-converting the two transmission signals 22 and 23 and multiplexing them. Then, the local light 120 is optically phase-modulated using the generated modulation signals 91a to 91d. As a result, the optical transmitter 11 according to the first embodiment enables a plurality of signal lights 24 and 25 to be wavelength-multiplexed and transmitted by a single optical transmitter.

  Furthermore, the optical transmitter 11 of the first embodiment does not require an optical multiplexer for wavelength multiplexing the signal lights 24 and 25. For this reason, the transmission distance of the optical transmitter 11 of the first embodiment is not limited by the loss of the optical demultiplexer.

  In other words, the optical transmitter 11 of the first embodiment enables a single unit to transmit a plurality of signal lights, thereby reducing the size and price of the optical transmitter and the transmission distance of the optical transmission system. There is an effect that it is possible to enlarge.

  In the present embodiment, the modulation schemes of the signal lights 24 and 25 are polarization multiplexing QPSK modulation and polarization multiplexing 16QAM modulation, respectively. However, these are merely examples, and the modulation method in the polarization multiplexing modulator 51 is not limited to these.

  Further, the above-described functions of the optical transmitter 11 may be realized by the CPU 95 executing a program for controlling each unit of the optical transmitter 11. The program is recorded in the memory 96.

(Second Embodiment)
FIG. 4 is a block diagram illustrating a configuration of the optical receiver 10 according to the second embodiment of this invention. The optical receiver 10 shown in FIG. 4 includes a local light source 30, a 90-degree optical hybrid circuit 50, light receiving elements 60a-60d, and AD conversion circuits 70a-70d. The optical receiver 10 further includes fixed equalizers (FEQ) 100 and 101, adaptive equalizers (AEQ) 120 and 121, and decoders 130 and 131.

  The optical receiver 10 simultaneously receives the signal lights 20 and 21 using the 90-degree optical hybrid circuit 50, the light receiving elements 60a-60d, and the AD conversion circuits 70a-70d, and performs coherent detection. The signal lights 20 and 21 are signal lights modulated by different transmission signals, respectively. The wavelengths of the signal lights 20 and 21 are different from each other.

  The signal light 20 is a polarization-multiplexed QPSK modulated signal, and is an X-polarized I (inphase) component (XI signal), an X-polarized Q (quadrature) component (XQ signal), and a Y-polarized I component. Four signals are included: (YI signal) and Q component of Y polarization (YQ signal). The baud rate of the XI signal, XQ signal, YI signal, and YQ signal is 25 Gbaud, and a total of 100 Gbps information is transmitted. The X polarization is orthogonal to the Y polarization.

  The signal light 21 is a polarization multiplexed 16QAM modulated signal. Similarly to the signal light 20, the signal light 21 includes an XI signal, an XQ signal, a YI signal, and a YQ signal. The light in which the signal lights 20 and 21 are wavelength-multiplexed is input to one of two inputs of a 90 ° optical hybrid circuit 50.

  The local light source 30 is a light source using a semiconductor laser or the like, and outputs a local light 40 that is combined with the signal lights 20 and 21. The local light 40 is input to the other input of the 90-degree optical hybrid circuit 50.

  The 90-degree optical hybrid circuit 50 is an optical circuit composed of an optical waveguide. The 90-degree optical hybrid circuit 50 combines the signal lights 20 and 21 and the local light 40, and outputs the combined light to the light receiving elements 60a-60d. The light receiving elements 60a-60d have an X-polarization axis I port output, an X-polarization axis Q-port output, a Y-polarization axis I-port output, and a Y-polarization axis Q, respectively. The combined light from the port output is input. The combined light includes both the signal light 20 and the signal light 21.

  The light receiving elements 60a-60d are, for example, photodiodes, and convert the combined light output from the 90-degree optical hybrid circuit 50 into analog electrical signals. The AD conversion circuits 70a to 70d perform analog to digital (A / D) conversion on the analog electric signals output from the light receiving elements 60a to 60d, and output the AD converted signals as reception signals 80a to 80d. The received signals 80a, 80b, 80c, and 80d are respectively the X polarization axis I port output, the X polarization axis Q port output, the Y polarization axis I port output, and the Y polarization of the 90-degree optical hybrid circuit 50. Corresponds to the Q port output of the axis. That is, the received signals 80a and 80b and 80c and 80d are signals corresponding to polarization components orthogonal to each other of the signal light input to the 90-degree optical hybrid circuit 50, respectively. The received signals 80a and 80c and 80b and 80d are signals corresponding to components detected by shifting the phase by 90 degrees with respect to the signal light input to the 90-degree optical hybrid circuit 50, respectively. These received signals 80a, 80b, 80c, and 80d are mixed with the XI signal, XQ signal, YI signal, and YQ signal of the signal lights 20 and 21. The XI signal, XQ signal, YI signal, and YQ signal are separated by adaptive equalization circuits 120 and 121 as described later.

  Note that the configuration including the local light source 30, the 90-degree optical hybrid circuit 50, the light receiving elements 60a-60d, and the AD conversion circuits 70a-70d for performing the above-described coherent detection of the polarization multiplexed signal light and each element The general operation is well known. For this reason, a more detailed description is omitted.

  FIG. 5 is a diagram illustrating an example of the wavelength spectrum and polarization of the signal lights 20 and 21. The “X polarization component” and “Y polarization component” in FIG. 5 both indicate the amplitude of the signal light. The signal lights 20 and 21 are signals that are wavelength-multiplexed at a very small wavelength interval of about 0.3 nm. In the present embodiment, the signal light 20 is subjected to polarization multiplexing QPSK modulation, and the information rate is 100 Gbps. The signal light 21 is polarization multiplexed 16QAM modulated, and the information rate is 100 Gbps. The spectra of the signal light 20 and the signal light 21 do not overlap.

  Reception signals 80a-80d converted into digital signals by AD conversion circuits 70a-70d are branched into two. The two-branched received signals 80a to 80d are digitally processed in the order of independent fixed equalization circuit 100 or 101, adaptive equalization circuit 120 or 121, and decoding circuit 130 or 131, respectively.

  FIG. 6 is a diagram illustrating a frequency spectrum of a signal in the optical receiver 10. Each vertical axis in FIG. 6 indicates the amplitude of the signal. Since the reception signals 80a to 80d are digitized by the AD conversion circuits 70a to 70d, (a) to (c) in FIG. 6 are obtained when it is assumed that the reception signal is converted to an analog signal by the DA conversion circuit. A virtual frequency spectrum is shown.

  FIG. 6A shows the frequency spectrum of the received signals 80a-80d. The reception signals 80a-80d include frequency spectra corresponding to the transmission signals 140 and 141 transmitted by the signal light 20 and the signal light 21. The frequency spectrum of the signal light 20 has a frequency band of about 50 GHz centering on -12.5 GHz. The frequency spectrum of the signal light 21 has a frequency band of about 25 GHz centering on +25 GHz.

  The reception signal of the signal light 20 and the reception signal of the signal light 21 are frequency-multiplexed at a frequency interval of 37.5 GHz. The wavelength interval of the optical carrier wave corresponding to this frequency interval (37.5 GHz) is 0.3 nm as shown in FIG. 5 when the wavelengths of the signal lights 20 and 21 are around 1550 nm.

  The fixed equalization circuits 100 and 101 perform chromatic dispersion compensation processing, frequency conversion processing, and filtering processing on the received signals 80a to 80d by digital processing. In the chromatic dispersion compensation process, the chromatic dispersion generated in the optical fiber transmission line is equalized. For the equalization processing, for example, a digital filter such as an FIR (finite impulse response) filter is used.

  The frequency spectrum of the reception signals 80a to 80d is shifted by the frequency conversion process in the fixed equalization circuit 100 so that the center frequency of the frequency spectrum corresponding to the signal light 20 becomes zero. Further, in the filtering process, only signals in the frequency band corresponding to the signal light 20 are left, and signals in other frequency bands are removed. As a result, as shown in FIG. 6B, the fixed equalization circuit 100 outputs reception signals 110a to 110d including only the transmission signal transmitted by the signal light 20.

  The fixed equalization circuit 101 also performs chromatic dispersion compensation processing, frequency conversion processing, and filtering processing on the input received signals 80a to 80d by the same procedure as the fixed equalization circuit 100. However, in the frequency conversion process in the fixed equalization circuit 101, the frequency spectrum of the reception signals 80a to 80d is shifted so that the center frequency of the frequency spectrum corresponding to the signal light 21 becomes zero. Further, in the filtering process, only signals in the frequency band corresponding to the signal light 21 are left, and signals in other frequency bands are removed. As a result, as shown in FIG. 6C, the fixed equalization circuit 101 outputs reception signals 111a to 111d including only the transmission signal transmitted by the signal light 21.

  Note that the procedure of chromatic dispersion compensation processing in the fixed equalization circuits 100 and 101 is the same as the procedure of chromatic dispersion compensation used in general digital coherent reception processing, and thus detailed description thereof is omitted.

  Received signals 110 a-110 d are input to adaptive equalization circuit 120. The adaptive equalization circuit 120 performs polarization separation processing, carrier frequency offset compensation processing, and carrier phase compensation processing on the received signals 110a to 110d. In the polarization separation process, the received signal is separated so as to correspond to the polarization at the time of transmission. In the carrier frequency offset compensation process, the difference between the frequency of the optical carrier and the frequency of the local light 40 is compensated. In the carrier phase compensation process, the phase fluctuation between the carrier wave and the local light 40 is compensated.

  The adaptive equalization circuit 120 performs polarization separation processing, carrier frequency offset compensation processing, and carrier phase compensation processing on the received signals 110a to 110d. The signal processed by the adaptive equalization circuit 120 is input to the decoding circuit 130. The decoding circuit 130 performs symbol identification processing, error correction processing, and frame generation processing on the signal processed by the adaptive equalization circuit 120. In the symbol identification process, the symbol of the received signal 20 is identified based on the signal constellation processed by the adaptive equalization circuit 120. Then, an error included in the signal is corrected by the error correction process and the frame generation process, and a predetermined frame including the signal is generated. As a result, the transmitted transmission signal 140 is restored.

  Received signals 111 a-111 d are subjected to the same processing as adaptive equalization circuit 120 and decoding circuit 130 by adaptive equalization circuit 121 and decoding circuit 131. As a result, the transmission signal 141 transmitted by the signal light 21 is restored. Note that the processing in the adaptive equalization circuits 120 and 121 and the decoding circuits 130 and 131 is the same as the procedure used in general digital coherent reception processing, and thus detailed description thereof is omitted.

  In this way, the optical receiver 10 outputs transmission signals 140 and 141 each having an information transmission rate of 100 Gbps.

  As described above, the optical receiver 10 of the second embodiment can receive wavelength-multiplexed signal light with a single optical receiver. Furthermore, the optical receiver 10 of the second embodiment does not require an optical demultiplexer to separate the signal lights 20 and 21. For this reason, in the optical receiver 10 of the second embodiment, the transmission distance is not limited by the loss of the optical demultiplexer.

  That is, the optical receiver 10 of the second embodiment enables a single unit to receive a plurality of signal lights, thereby reducing the size and price of the optical receiver and the transmission distance of the optical transmission system. There is an effect that it is possible to enlarge.

  In the present embodiment, the modulation schemes of the signal lights 20 and 21 are polarization multiplexing QPSK modulation and polarization multiplexing 16 QAM modulation, respectively. However, the modulation schemes of the signal lights 20 and 21 are not limited to these.

  Further, the above-described functions of the optical receiver 10 may be realized by the CPU 95 executing a program for controlling each unit of the optical receiver 10. The program is recorded in the memory 96.

(Third embodiment)
FIG. 7 is a block diagram illustrating a configuration of the optical receiver 20 according to the third embodiment of this invention. In the subsequent drawings, the same elements as those in the above-described drawings are denoted by the same reference numerals, and redundant description is omitted.

  7 includes a local light source 30, a 90-degree optical hybrid circuit 50, light receiving elements 60a-60d, AD conversion circuits 70a-70d, a fixed equalization circuit 100A, adaptive equalization circuits 120 and 121, and a decoding circuit. 130 and 131 are provided. 7, the functions and operations of the local light source 30, the 90-degree optical hybrid circuit 50, the light receiving elements 60a-60d, the AD conversion circuits 70a-70d, the adaptive equalization circuits 120 and 121, and the decoding circuits 130 and 131 are shown in FIG. This is the same as the optical receiver 10 described.

  In FIG. 7, signal lights 20 and 21 are signal lights modulated by different transmission signals, respectively. The wavelengths of the signal lights 20 and 21 are different from each other, and the spectra do not overlap. The relationship between the polarization and the wavelength of the signal lights 20 and 21 in the third embodiment is shown in FIG. 5 as in the second embodiment. The optical receiver 20 simultaneously receives the signal lights 20 and 21 using the 90-degree optical hybrid circuit 50, the light receiving elements 60a-60d, and the AD conversion circuits 70a-70d.

  The AD conversion circuits 70a to 70d perform AD conversion on the analog electrical signals input from the light receiving elements 60a to 60d, and output the converted signals as reception signals 80a to 80d. The processing in the optical receiver 20 so far is the same as in the second embodiment.

  FIG. 8 is a block diagram illustrating a configuration of a fixed equalization circuit 100A according to the third embodiment. The fixed equalization circuit 100A includes four subunits 100a to 100d. The subunit 100a includes a fast Fourier transform circuit 110, multiplication circuits 130 (1) -130 (N) and 131 (1) -131 (N), inverse Fourier transform circuits 150 and 151, and coefficient setting circuits 160 and 161, respectively. Prepare. The subunits 100b to 100d also have the same configuration as the subunit 100a.

  The subunit 100a processes the received signal 80a and outputs received signals 200a and 201a. Similarly, the subunits 100b-100d process the received signals 80b-80d, respectively, and output received signals 200b-200d and 201b-201d. The operation of the subunits 100a to 100d will be described later.

  FIG. 9 is a diagram illustrating a frequency spectrum of a signal of each part of the optical receiver 20. Each vertical axis in FIG. 9 indicates the amplitude of the signal. The reception signal of the optical receiver 20 is digitized by AD conversion circuits 70a to 70d. For this reason, FIG. 9 shows a virtual frequency spectrum when it is assumed that the received signal is converted into an analog signal by the DA converter circuit. As shown in FIG. 9A, the received signals 80a-80d output from the AD conversion circuit include the frequency spectrum of the signal light 20 and the signal light 21. The signal light 20 and the signal light 21 are multiplexed at a frequency interval of 37.5 GHz. The frequency spectrum of the signal light 20 has a frequency band of about 50 GHz centering on -12.5 GHz. The frequency spectrum of the signal light 21 has a frequency band of about 25 GHz centering on +25 GHz.

  The fixed equalization circuit 100A performs chromatic dispersion compensation processing, frequency conversion processing, and filtering processing on each of the frequency spectra of the signal lights 20 and 21 included in the reception signals 80a to 80d. Since these chromatic dispersion compensation processing, frequency conversion processing, and filtering processing are the same as the processing of the fixed equalization circuit 100 in the second embodiment, description of each processing is omitted.

  In the third embodiment, as shown in FIG. 8, the received signal 80a is converted into a frequency domain signal by the fast Fourier transform circuit 110 in the subunit 100a. The fast Fourier transform circuit 110 outputs the received signal 80a as a signal (frequency component) separated into N (N is a natural number) signals 120 (1) -120 (N) having an interval Δf. The frequency components 120 (1), 120 (2)... 120 (N) are signals having frequencies of Δf, 2Δf,.

  The frequency components 120 (1) -120 (N) output from the fast Fourier transform circuit 110 are branched into two. One of the branched frequency components is multiplied by coefficients C1, C2,... C (N) by multiplication circuits 130 (1) -130 (N), respectively. One of the branched frequency components is converted into frequency components 140 (1) -140 (N) by multiplication. The frequency components 140 (1) -140 (N) are converted into a time-domain received signal 200a by the inverse fast Fourier transform circuit 150.

  The coefficients C1, C2,... C (N) are set by the coefficient setting circuit 160 based on the chromatic dispersion compensation amount 170, the frequency shift amount 180, the filter band setting amount 190, and the like.

  In this embodiment, the coefficient setting circuit 160 assumes that the chromatic dispersion compensation amount 170 is −20000 ps / nm, the frequency shift amount 180 is +12.5 GHz, and the filter band setting amount 190 is 50 GHz. • C (N) is set. In this case, as shown in FIG. 9B, the received signal 200a is frequency-shifted so that the center frequency is zero and the frequency spectrum of the signal light 20 compensated for the chromatic dispersion of 20000 ps / nm. Only included.

  Similarly, the other of frequency components 120 (1) -120 (N) separated into two is multiplied by coefficients D1, D2,... D (N) by multiplication circuits 131 (1) -131 (N). Is done. By multiplication, the other of the branched frequency components is converted into frequency components 141 (1) -141 (N). The frequency components 141 (1) -141 (N) are converted into the received signal 201a by the inverse fast Fourier transform circuit 151.

  The values input to the coefficient setting circuit 161 for setting the coefficients D1, D2,... D (N) are, for example, a chromatic dispersion compensation amount 171 of −10000 ps / nm and a frequency shift amount 181 of −25 GHz. The filter band setting amount 191 is 25 GHz. In this case, as shown in FIG. 9C, the received signal 200a includes only the frequency spectrum of the signal light 21 that has been frequency shifted so that the center frequency becomes zero and whose chromatic dispersion is compensated.

  The subunits 100b to 100d perform the same processing as the subunit 100a on the received signals 80b to 80d, respectively. Then, received signals 200b-200d and 201b-201d are output from the subunits 100b-100d, respectively.

  Received signals 200a to 200d output from fixed equalization circuit 100 are subjected to polarization separation processing, carrier frequency offset compensation processing, and carrier phase compensation processing in adaptive equalization circuit 120. The signal processed by the adaptive equalization circuit 201 is further subjected to signal identification processing, error correction processing, and frame generation processing by the decoding circuit 130, and is output as a transmission signal 230. In this way, the received signals 200a-200d are finally converted into a transmission signal 230 having an information transmission rate of 100 Gbps.

  Similarly, the received signals 201a to 201d output from the fixed equalization circuit 100 are subjected to polarization separation processing, carrier frequency offset compensation processing, and carrier phase compensation processing by the adaptive equalization circuit 121. The signal processed by the adaptive equalization circuit 211 is further subjected to signal identification processing, error correction processing, and frame generation processing by the decoding circuit 131, and is output as a transmission signal 231. In this way, the reception signals 201a to 201d are finally converted into a transmission signal 231 having an information transmission rate of 100 Gbps.

  Note that the processing in the adaptive equalization circuits 120 and 121 and the decoding circuits 130 and 131 is the same as the procedure used in general digital coherent reception processing, as in the second embodiment, and thus detailed description thereof is omitted. To do.

  As described above, in the optical receiver 20 of the third embodiment, the subunits 100a to 100d including the fast Fourier transform circuit and the inverse fast Fourier transform circuit perform the Fourier transform on the signal including the signal lights 20 and 21. Do it all at once. As a result, the optical receiver 20 of the third embodiment can receive the wavelength-multiplexed signal light with a single optical receiver. That is, the optical receiver 20 of the third embodiment can also transmit a plurality of signal lights by one unit similarly to the optical receiver 10 of the second embodiment.

  Further, the optical receiver 20 of the third embodiment also does not require an optical demultiplexer in order to separate the signal lights 20 and 21. For this reason, the transmission distance of the optical receiver 20 of the third embodiment is not limited by the loss of the optical demultiplexer.

  As described above, the optical receiver 20 of the third embodiment also has an effect that the optical receiver can be reduced in size and price, and the transmission distance of the optical transmission system can be increased.

  In the third embodiment, the modulation schemes of the signal lights 20 and 21 are polarization multiplexing QPSK modulation and polarization multiplexing 16QAM modulation, respectively. However, the modulation schemes of the signal lights 20 and 21 are not limited to these.

  Further, the above-described functions of the optical receiver 20 may be realized by the CPU 95 executing a program for controlling each unit of the optical receiver 20. The program is recorded in the memory 96.

(Fourth embodiment)
FIG. 10 is a block diagram illustrating a configuration of an optical transmission system 700 according to the fourth embodiment of this invention. In the optical transmission system 700, the optical transmitter 11 of the first embodiment and the optical receiver 10 of the second embodiment or the optical receiver 20 of the third embodiment are connected to face each other. The optical transmitter 11 transmits the signal lights 24 and 25 described in FIG. 1 to the optical receiver 10 or 20. The signal lights 24 and 25 are received by the optical receiver 10 described in FIG. 4 as the signal lights 20 and 21. Alternatively, the signal lights 24 and 25 are received by the optical receiver 20 described in FIG. That is, in this optical transmission system, wavelength-multiplexed signal light can be transmitted by one optical transmitter and one optical receiver.

  In other words, the optical transmission system 700 can transmit a plurality of signal lights with one optical transmitter and one optical receiver. Therefore, the optical transmission system 700 has the effects of the first and second embodiments or the effects of the first and third embodiments.

(Fifth embodiment)
FIG. 11 is a block diagram illustrating a configuration of an optical transmitter 800 according to the fifth embodiment of this invention. The optical transmitter 800 includes a frequency conversion unit 810, a multiplexing unit 820, and an optical modulation unit 830.

  The frequency conversion unit 810 converts the frequency bands of the plurality of input electrical signals 840 into frequency bands that do not overlap each other, and outputs the converted signal 850 to the multiplexing unit 820. The multiplexing unit 820 frequency-multiplexes the electrical signal 850 frequency-converted by the frequency conversion unit 810 and outputs the result to the optical modulation unit 830. The optical modulator 830 modulates the optical carrier 880 with the frequency-multiplexed electric signal 860 and outputs the signal light 870.

  The optical transmitter 800 of the fifth embodiment frequency-multiplexes and multiplexes a plurality of electrical signals, and modulates an optical carrier wave using the multiplexed electrical signal 860. By modulating the optical carrier wave with the multiplexed electrical signal 860, signal light having a different wavelength is generated for each multiplexed signal. As a result, the optical transmitter 800 according to the fifth embodiment enables a plurality of optical carriers to be wavelength-multiplexed and transmitted by one optical transmitter.

  That is, the single optical transmitter 800 of the fifth embodiment can transmit a plurality of signal lights. Furthermore, the optical transmitter 800 of the fifth embodiment does not require an optical multiplexer in order to wavelength multiplex an optical carrier wave. For this reason, the transmission distance of the optical transmitter 800 of the fifth embodiment is not limited by the loss of the optical multiplexer.

  As described above, the optical transmitter 800 of the fifth embodiment also has the effect that the optical transmitter can be reduced in size and price, and the transmission distance of the optical transmission system can be increased.

(Sixth embodiment)
FIG. 12 is a block diagram illustrating a configuration of an optical receiver 900 according to the sixth embodiment of this invention. The optical receiver 900 includes a detection unit 910 and a frequency conversion unit 920.

  The detection unit 910 is input with signal light 930 obtained by wavelength-multiplexing a plurality of optical carriers having different wavelengths that are phase-modulated by different transmission signals. The spectra of the plurality of optical carriers do not overlap each other. Then, the detection unit 910 outputs the detected signal 950 by mixing the signal light 930 with the local light 940. The frequency conversion unit 920 extracts the detected signal from the detected signal 950 for each frequency band in which each transmission signal is included, and outputs the extracted signal as a received signal 960.

  The optical receiver 900 of the sixth embodiment having such a configuration can extract a transmission signal transmitted by each optical carrier from a signal obtained by detecting signal light in which a plurality of optical carriers are wavelength-multiplexed. That is, a single optical receiver 900 according to the sixth embodiment can transmit a plurality of signal lights. Furthermore, the optical receiver 900 of the sixth embodiment does not require an optical demultiplexer to separate signal light. For this reason, the transmission distance of the optical receiver 900 of the second embodiment is not limited by the loss of the optical demultiplexer.

  As described above, the optical transmitter 900 according to the sixth embodiment also has an effect that the optical receiver can be reduced in size and price, and the transmission distance of the optical transmission system can be increased.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes 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.

  In addition, although embodiment of this invention can be described also as the following additional remarks, it is not limited to these.

(Appendix 1)
A frequency conversion means for converting a frequency band of a plurality of electrical signals into a frequency band that does not overlap each other for each electrical signal, and outputting the converted electrical signal;
Multiplexing means for frequency-multiplexing the converted electrical signal and outputting the frequency-multiplexed electrical signal;
An optical modulator that modulates an optical carrier wave by the frequency-multiplexed electrical signal and outputs signal light;
An optical transmitter.

(Appendix 2)
An encoding circuit for converting each of the electrical signals into four parallel signals corresponding to the modulation scheme of the optical modulator;
The frequency conversion means converts the frequency band of the parallel signal into a frequency band that does not overlap each other for each electrical signal,
The optical modulator converts the four parallel signals into an XI (inphase) signal having a first polarization X, an XQ (quadrature) signal whose phase is orthogonal to the XI signal, and the first polarization, respectively. Performing a polarization multiplexing phase modulation on the parallel signal as a YI signal having a second polarization Y orthogonal to X and a YQ signal having a phase orthogonal to the YI signal,
The optical transmitter according to appendix 1.

(Appendix 3)
The optical transmitter according to appendix 1 or 2, further comprising a local light source that generates the optical carrier wave.

(Appendix 4)
Detecting means for inputting a signal light in which optical carriers having different wavelengths, which are phase-modulated by different electric signals, are wavelength-multiplexed, and outputting a signal detected by mixing the signal light with local light;
Frequency conversion means for extracting and outputting a received signal for each frequency band in which each of the electrical signals is included from the detected signal;
An optical receiver.

(Appendix 5)
The electrical signal includes a first transmission signal and a second transmission signal,
The signal light includes a first signal light that is polarization-multiplexed and phase-modulated with a first transmission signal, and a second signal light that is polarization-multiplexed and phase-modulated with a second transmission signal,
The detection means includes
An XI ′ (inphase) signal having a first polarization X ′ for each of the first signal light and the second signal light by detecting the first signal light and the second signal light. The XQ ′ (quadrature) signal whose phase is orthogonal to the XI ′ signal, the YI ′ signal having the second polarization Y ′ orthogonal to the first polarization X ′, and the phase orthogonal to the YI ′ signal Outputting the YQ ′ signal as the detected signal;
The optical receiver described in the supplementary note 4, wherein

(Appendix 6)
The frequency conversion means includes a first frequency conversion means and a second frequency conversion means,
The detected signal is input to the first frequency converting means and the second frequency converting means,
The first frequency converting means performs the chromatic dispersion compensation process on the detected signal, and a frequency band in which the first transmission signal is included from the detected signal subjected to the chromatic dispersion compensation process. The signal is extracted and output,
The second frequency converting means performs the chromatic dispersion compensation processing on the detected signal, and a frequency band in which the second transmission signal is included from the detected signal subjected to the chromatic dispersion compensation processing. Extract and output the signal of
An optical receiver according to appendix 4 or 5, characterized by the above.

(Appendix 7)
The frequency conversion means includes
A fast Fourier transform circuit that performs fast Fourier transform on the input detection signal and outputs a signal for each frequency component; and
A first multiplication circuit that multiplies one signal obtained by bifurcating the signal for each frequency component by a first coefficient;
A first inverse fast Fourier transform circuit for performing an inverse fast Fourier transform and outputting the multiplication result of the first multiplication means;
A second multiplication circuit for multiplying the other signal obtained by bifurcating the signal for each frequency component by a second coefficient;
A second inverse fast Fourier transform circuit for performing an inverse fast Fourier transform and outputting the multiplication result of the second multiplication means;
Comprising a subunit comprising
The optical receiver according to appendix 5, wherein the subunit is provided for each of the XI signal, the XQ signal, the YI signal, and the YQ signal.

(Appendix 8)
The first and second coefficients have a chromatic dispersion compensation amount given to a signal output from the fast Fourier transform circuit, and a frequency necessary for extracting the first and second transmission signals. The optical receiver according to appendix 7, wherein the optical receiver is set based on information.

(Appendix 9)
An optical transmission system arranged so that the optical receiver described in Appendix 4 can receive the signal light transmitted by the optical transmitter described in Appendix 1.

(Appendix 10)
An optical transmission system arranged so that the optical receiver described in Appendix 5 can receive the signal light transmitted by the optical transmitter described in Appendix 2.

(Appendix 11)
A frequency band of a plurality of electrical signals are converted into frequency bands that do not overlap each other for each electrical signal, and the converted electrical signal is output,
Frequency-multiplexing the converted electrical signal to output the frequency-multiplexed electrical signal;
Modulating an optical carrier wave with the frequency-multiplexed electrical signal to output signal light;
Optical transmission method.

(Appendix 12)
Outputs a signal detected by mixing the signal light, which is phase-modulated with different electrical signals and wavelength-multiplexed with optical carriers having different wavelengths, with local light,
From the detected signal, a reception signal extracted for each frequency band in which each of the electrical signals is included is output.
Optical reception method.

(Appendix 13)
To the computer of the optical transmitter,
A procedure for converting a frequency band of a plurality of electrical signals into a frequency band that does not overlap each other for each electrical signal, and outputting the converted electrical signal;
A step of frequency-multiplexing the converted electrical signal and outputting the frequency-multiplexed electrical signal;
A procedure of modulating the optical carrier wave with the frequency-multiplexed electrical signal and outputting signal light,
An optical transmitter control program for executing

(Appendix 14)
To the optical receiver computer,
A procedure for outputting a detected signal by mixing signal light in which optical carriers having different wavelengths, which are phase-modulated with different electrical signals, are wavelength-multiplexed with local light,
A procedure for outputting a reception signal extracted from the detected signal for each frequency band in which each of the electrical signals is included,
An optical receiver control program for executing

10, 20 Optical receiver 11 Optical transmitter 22, 23, 230, 231 Transmission signal 24, 25 Signal light 42a-42d, 43a-43d, 62a-62d, 63a-63d, 91a-91d Modulated signal 32, 33 Encoding Circuit 52, 53 Frequency conversion circuit 60a-60d Light receiving element 70a-70d AD conversion circuit 71a-71d Multiplex circuit 80a-80d Received signal 81a-81d DA conversion circuit 50 90 degree optical hybrid circuit 51 Polarization multiple modulator 30, 110 Local Light source 100, 100A Fixed equalization circuit 120, 121 Adaptive equalization circuit 130, 131 Decoding circuit 110a-110d, 111a-111d Received signal 700 Optical transmission system 800 Optical transmitter 810 Frequency conversion unit 820 Multiplexing unit 830 Optical modulation unit 840 Electricity Signal 850 frequency converted Electrical signal 860 frequency-multiplexed electrical signal 870 signal light 880 optical carrier 900 optical receiver 910 detecting unit 920 frequency conversion unit 930 the signal light 940 local light 950 detected signal 960 received signal

Claims (10)

A frequency conversion means for converting a frequency band of a plurality of electrical signals into a frequency band that does not overlap each other for each transmission signal, and outputting the converted electrical signal;
Multiplexing means for frequency-multiplexing the converted electrical signal and outputting the frequency-multiplexed electrical signal;
An optical modulator that modulates an optical carrier wave by the frequency-multiplexed electrical signal and outputs signal light;
An optical transmitter. An encoding circuit that converts each of the transmission signals into four parallel signals corresponding to the modulation scheme of the optical modulator;
The frequency conversion means converts the frequency band of the parallel signal into a frequency band that does not overlap each other for each electrical signal,
The optical modulator converts the four parallel signals into an XI (inphase) signal having a first polarization X, an XQ (quadrature) signal whose phase is orthogonal to the XI signal, and the first polarization, respectively. Performing a polarization multiplexing phase modulation on the parallel signal as a YI signal having a second polarization Y orthogonal to X and a YQ signal having a phase orthogonal to the YI signal,
The optical transmitter according to claim 1. Detecting means for inputting a signal light in which optical carriers having different wavelengths, which are phase-modulated by different electric signals, are wavelength-multiplexed, and outputting a signal detected by mixing the signal light with local light;
Frequency conversion means for extracting and outputting a received signal for each frequency band in which each of the electrical signals is included from the detected signal;
An optical receiver. The electrical signal includes a first transmission signal and a second transmission signal,
The signal light includes a first signal light that is polarization-multiplexed and phase-modulated with a first transmission signal, and a second signal light that is polarization-multiplexed and phase-modulated with a second transmission signal,
The detection means includes
An XI ′ (inphase) signal having a first polarization X ′ for each of the first signal light and the second signal light by detecting the first signal light and the second signal light. The XQ ′ (quadrature) signal whose phase is orthogonal to the XI ′ signal, the YI ′ signal having the second polarization Y ′ orthogonal to the first polarization X ′, and the phase orthogonal to the YI ′ signal Outputting the YQ ′ signal as the detected signal;
The optical receiver according to claim 3. The frequency conversion means includes a first frequency conversion means and a second frequency conversion means,
The detected signal is input to the first frequency converting means and the second frequency converting means,
The first frequency converting means performs the chromatic dispersion compensation process on the detected signal, and a frequency band in which the first transmission signal is included from the detected signal subjected to the chromatic dispersion compensation process. The signal is extracted and output,
The second frequency converting means performs the chromatic dispersion compensation processing on the detected signal, and a frequency band in which the second transmission signal is included from the detected signal subjected to the chromatic dispersion compensation processing. Extract and output the signal of
The optical receiver according to claim 3 or 4, characterized by the above-mentioned. The frequency conversion means includes
A fast Fourier transform circuit that performs fast Fourier transform on the input detection signal and outputs a signal for each frequency component; and
First multiplication means for multiplying one signal obtained by bifurcating the signal for each frequency component by a first coefficient;
A first inverse fast Fourier transform circuit for performing an inverse fast Fourier transform and outputting the multiplication result of the first multiplication means;
Second multiplication means for multiplying the other signal obtained by bifurcating the signal for each frequency component by a second coefficient;
A second inverse fast Fourier transform circuit for performing an inverse fast Fourier transform and outputting the multiplication result of the second multiplication means;
Comprising a subunit comprising
The optical receiver according to claim 4, wherein the subunit is provided for each of the XI signal, the XQ signal, the YI signal, and the YQ signal.   The first and second coefficients have a chromatic dispersion compensation amount given to a signal output from the fast Fourier transform circuit, and a frequency necessary for extracting the first and second transmission signals. The optical receiver according to claim 6, wherein the optical receiver is set based on information.   An optical transmission system arranged so that the optical receiver described in claim 3 can receive the signal light transmitted by the optical transmitter described in claim 1. A frequency band of a plurality of electrical signals are converted into frequency bands that do not overlap each other for each electrical signal, and the converted electrical signal is output,
Frequency-multiplexing the converted electrical signal to output the frequency-multiplexed electrical signal;
Modulating an optical carrier wave with the frequency-multiplexed electrical signal to output signal light;
Optical transmission method. Outputs a signal detected by mixing the signal light, which is phase-modulated with different electrical signals and wavelength-multiplexed with optical carriers having different wavelengths, with local light,
From the detected signal, a reception signal extracted for each frequency band in which each of the electrical signals is included is output.
Optical reception method.

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