Optical transmitter, optical receiver, optical transmission method, and optical reception method

Abstract

An optical transmitter comprising a multiplexed signal generation unit for multiplexing a plurality of narrow-band signals and generating a broadband optical modulated signal, and a semiconductor optical amplifier for amplifying the intensity of the broadband optical modulated signal.

Description

[Technical field]

[0001] The present invention relates to an optical transmitter, an optical receiver, an optical transmitting method, and an optical receiving method. [Background technology]

[0002] As the capacity of optical transmission systems increases, the size and power consumption of optical transceivers are also increasing. In order to reduce the size and power consumption of optical transceivers, research and development is being conducted on an integrated optical module called IC-TROSA (integrated coherent transmit-receiver optical subassembly), which integrates a tunable laser, a driver amplifier, an optical modulator, a photodetector, etc. (see Non-Patent Document 1).

[0003] Semiconductor optical amplifiers (SOAs) are small and consume low power, so they can be used as optical preamplifiers in optical modules such as IC-TROSA. Non-Patent Document 2 describes a configuration in which a semiconductor optical amplifier is incorporated as an optical preamplifier for an IC-TROSA with a data transmission speed of 400-600 Gb / s and a symbol rate of 64 GBd. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Implementation Agreement for Integrated Coherent Transmit-Receive Optical Sub Assembly,” OIF-IC-TROSA [Non-Patent Document 2] J. Zhou, et al., “Characterizations of Semiconductor Optical Amplifiers for 64Gbaud 16-64QAM Coherent Optical Transceivers,” OFC2019, Tu2H.7 [Non-Patent Document 3] AAM Saleh, “Nonlinear Models of Traveling-wave Optical Amplifiers,” Electronics Letters, vol.24, no.14, pp.835-837, 1988. [Non-Patent Document 4] N. Kamitani, Y. Yoshida, and K. Kitayama, “Experimental Study on Impact of SOA Nonlinear Phase Noise in 40Gbps Coherent 16QAM Transmissions,” ECOC2012, P1.04. [Non-Patent Document 5] S. Okamoto, M. Yoshida, K. Yonenaga, and T. Kataoka. “Adaptive Pre-equalization using Bidirectional Pilot Sequences to Estimate and Feed Back Amplitude Transfer Function and Chromatic Dispersion,” OFC2015 Th2A.29. Summary of the Invention [Problem to be solved by the invention]

[0005] However, the symbol rate of the optically modulated signal handled by the optical transceiver is usually several tens of GBd. The fluctuation time of the optically modulated signal is the inverse of the symbol rate, which is approximately several tens of ps. The carrier lifetime of a semiconductor optical amplifier is usually several hundred ps, which is close to the fluctuation time of the optically modulated signal, and therefore nonlinear distortion caused by the semiconductor optical amplifier may occur in the optically modulated signal. Under such conditions, when the injection current to the semiconductor optical amplifier is increased to drive the semiconductor optical amplifier at a high optical gain, the nonlinear distortion caused by the semiconductor optical amplifier increases, causing a significant performance degradation of the optically modulated signal. An object of the present invention is to provide a technique capable of reducing the influence of nonlinear distortion caused by a semiconductor optical amplifier. [Means for solving the problem]

[0006] One aspect of the present invention is an optical transmitter comprising: a multiplexed signal generator that multiplexes a plurality of narrowband signals to generate a wideband optical modulated signal; and a semiconductor optical amplifier that amplifies the intensity of the wideband optical modulated signal.

[0007] One aspect of the present invention is an optical receiver including a semiconductor optical amplifier that amplifies the intensity of a wideband optical modulated signal, and a multiplexed signal demultiplexer that demultiplexes the wideband optical modulated signal into narrowband signals.

[0008] One aspect of the present invention is an optical transmission method comprising: a multiplexed signal generating step of multiplexing a plurality of narrowband signals to generate a wideband optical modulated signal; and a semiconductor optical amplifying step of amplifying the intensity of the wideband optical modulated signal.

[0009] One aspect of the present invention is an optical receiving method comprising a semiconductor optical amplification step of amplifying the intensity of a wideband optical modulated signal, and a multiplexed signal demultiplexing step of demultiplexing the wideband optical modulated signal into narrowband signals. Effect of the Invention

[0010] The techniques of the present invention can reduce the effects of nonlinear distortion caused by semiconductor optical amplifiers. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a configuration of an optical transmission system 1 according to a first embodiment. [Diagram 2] 1 is a diagram illustrating a configuration of an optical transmitter 2 according to a first embodiment. [Diagram 3] 4 is a flowchart showing an operation of the optical transmitter 2 according to the first embodiment. [Figure 4] 1 is a modified example of the optical transmitter 2 according to the first embodiment. [Diagram 5]1 is a diagram illustrating a configuration of an optical receiver 4 according to a first embodiment. [Figure 6] 5 is a flowchart showing the operation of the optical receiver 4 according to the first embodiment. [Figure 7] 1 is a modified example of the optical receiver 4 according to the first embodiment. [Figure 8] FIG. 11 is a diagram illustrating a configuration of an optical transmitter 2 according to a second embodiment. [Figure 9] 10 is a flowchart showing an operation of the optical transmitter 2 according to the second embodiment. [Figure 10] FIG. 11 is a diagram illustrating a configuration of an optical receiver 4 according to a second embodiment. [Figure 11] 10 is a flowchart showing the operation of the optical receiver 4 according to the second embodiment. [Figure 12] FIG. 11 is a diagram showing the configurations of a digital signal processing unit 21 and a digital signal processing unit 43 according to a third embodiment. [Figure 13] 1 is a table showing a signal space diagram under each condition. [Figure 14] 1 is a graph showing the relationship between the magnitude of the injection current (SOA injection current) into a semiconductor optical amplifier and the SNR penalty. [Figure 15] 1 is a diagram illustrating an optical transceiver 100 according to an embodiment of the present invention. [Figure 16] 1 is a diagram illustrating an optical transceiver 100 that performs polarization multiplexing according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First Embodiment FIG. 1 is a diagram showing a configuration of an optical transmission system 1 according to a first embodiment. The optical transmission system 1 is a communication device that uses an optical signal. The optical transmission system includes an optical transmitter 2, a transmission path 3, and an optical receiver 4. The optical transmitter 2 is a communication device that transmits an optical signal. The transmission path 3 transmits the optical signal transmitted from the optical transmitter 2 to the optical receiver 4. The optical receiver 4 is a communication device that receives the optical signal.

[0013] 2 is a diagram showing a configuration of an optical transmitter 2 according to the first embodiment. The optical transmitter 2 includes a digital signal processing unit 21, a multiplexed signal generating unit 22, and a semiconductor optical amplifier 23. The multiplexed signal generating unit 22 is realized by a broadband signal generating unit 221, an optical modulation unit 222, and a signal light source 223.

[0014] The digital signal processing unit 21 includes a signal generating unit 211, a band dividing unit 212, a narrowband signal processing unit 213, and a digital-to-analog conversion unit 214. The signal generating unit 211 generates a modulated signal sequence (I(n), Q(n)) from a transmission data sequence that is binary information. I(n) and Q(n) are electrical signals indicating an in-phase component and a quadrature component of a modulated signal. The signal generating unit 211 outputs the generated modulated signal sequence (I(n), Q(n)) to the band dividing unit 212. The band dividing unit 212 divides the modulated signal sequence input from the signal generating unit 211 into narrowband signals and inputs them to the narrowband signal processing unit 213. The narrowband signals are signals with a narrower band than the modulated signal sequence. The narrowband signal processing unit 213 performs addition and subtraction processing between narrowband signals and inputs them to the digital-to-analog conversion unit 214.

[0015] The digital-to-analog converter 214 converts the modulated signal sequence input from the narrowband signal processor 213 into an analog signal. The digital-to-analog converter 214 converts the converted analog signal sequence (I 1 ''(t),Q 1 ''(t)) and (I 2 ''(t),Q 2 The signal generator 221 outputs the signal ''(t) to the wideband signal generator 221.

[0016] Wideband signal generation section 221 generates a wideband signal from a plurality of narrowband analog signals that have been pre-processed by band division section 212 and narrowband signal processing section 213 and input from digital-analog conversion section 214 . Any method can be used to divide the modulated signal sequence into narrowband signals in the band division unit 212, add or subtract narrowband signals in the narrowband signal processing unit 213, and generate a wideband signal from a plurality of narrowband analog signals in the wideband signal generation unit 221. For example, the following process is performed using the method disclosed in JP 2018-019255 A.

[0017] The band division unit 212 divides the modulated signal sequence (I(n),Q(n)) input from the signal generation unit 211 into an upper sideband and a lower sideband, and shifts the frequency. The band division unit 212 divides the frequency-shifted upper sideband signal (narrowband signal, (I 1 '(n),Q 1 '(n)) and the lower sideband signal (narrowband signal (I 2 '(n),Q 2 '(n)) to narrowband signal processing section 213.

[0018] The narrowband signal processing unit 213 performs at least one of addition and subtraction between the upper sideband and the lower sideband for the upper sideband signal and the lower sideband signal input from the band division unit 212. The narrowband signal processing unit 213 outputs the narrowband signal (I 1 ''(n),Q 1 ''(n) and (I 2 ''(n),Q 2 The digital-to-analog converter 214 outputs the signal (n) to the digital-to-analog converter 214.

[0019] The broadband signal generating unit 221 performs frequency shifting on each of the multiple analog signals input from the digital-analog converting unit 214. The broadband signal generating unit 221 performs processing to add the multiple frequency-shifted analog signals together to generate a wideband signal. The bandwidth of the wideband signal is wider than the bandwidth of the analog signals to be added. The broadband signal generating unit 221 outputs the generated wideband signal (I(t), Q(t)) to the optical modulating unit 222. Since the wideband signal (I(t), Q(t)) is generated by adding together multiple different frequency-shifted analog signal sequences, the frequency band of the wideband signal sequence is wider than the frequency band of the analog signal sequence.

[0020] The optical modulation unit 222 generates a wideband optical modulated signal by modulating the optical signal as a carrier wave output from the signal light source 223 with the wideband signal input from the wideband signal generation unit 221. The optical modulation unit 222 outputs the generated wideband optical modulated signal to the semiconductor optical amplifier 23.

[0021] The semiconductor optical amplifier 23 amplifies the intensity of the wideband optical modulated signal input from the optical modulator 222. The semiconductor optical amplifier 23 outputs the amplified optical modulated signal to the optical receiver 4 via the transmission line 3. It is also possible to configure the modulated signal sequence to be divided into three or more narrowband signals and output from the digital-to-analog converter to generate a broadband optical modulated signal. A driver amplifier may be inserted between the broadband signal generating unit 221 and the optical modulation unit 222 to amplify the broadband signal. The multiplexed signal generating unit 22 may be configured by integrating the broadband signal generating unit 221 and the optical modulation unit 222. A signal light source 223 and a driver amplifier may be added to this integrated multiplexed signal generating unit 22 and integrated. The narrowband signal processing unit 213 may be configured as an analog circuit and inserted between the digital-analog conversion unit 214 and the broadband signal generating unit 221. Also, the narrowband signal processing unit 213 may be added to the integrated multiplexed signal generating unit 22 and integrated.

[0022] 3 is a flowchart showing the operation of the optical transmitter 2 according to the first embodiment. The signal generating unit 211 generates a modulated signal (step S1). The band dividing unit 212 converts the modulated signal into a narrowband signal (step S2). The broadband signal generating unit 221 generates a broadband signal based on a plurality of narrowband signals (step S3). The optical modulating unit 222 generates a broadband optical modulated signal based on the broadband signal (step S4). The semiconductor optical amplifier 23 amplifies the broadband optical modulated signal (step S5).

[0023] As described above, the optical transmitter 2 according to the first embodiment generates a wideband signal based on a plurality of narrowband signals, the wideband signal being wider than the narrowband signals. Since the fluctuation time of the wideband optical modulated signal is equal to the reciprocal of the optical signal band, the wideband optical modulated signal generated based on the wideband signal has a shorter fluctuation time than the optical modulated signal generated based on a signal having a band narrower than the wideband signal. Therefore, the optical transmitter 2 according to the first embodiment can make the fluctuation time of the optical modulated signal sufficiently shorter than the carrier lifetime of the semiconductor optical amplifier. Therefore, the optical transmitter 2 according to the first embodiment can reduce the influence of nonlinear distortion caused by the semiconductor optical amplifier.

[0024] To generate a wideband signal, a digital-to-analog converter (DAC) and an analog-to-digital converter (ADC) capable of high speed operation are indispensable, but the analog output bandwidth of a DAC and an ADC created using a CMOS (Complementary Metal Oxide Semiconductor) platform is insufficient at about 30 GHz. However, the wideband signal generated by the optical transmitter 2 according to the first embodiment has a sufficiently wide bandwidth.

[0025] The optical transmitter 2 according to the first embodiment may have a configuration as shown in Fig. 4. As shown in the figure, the optical transmitter 2 according to the first embodiment may output independent narrowband signals from a plurality of digital signal processing units (digital signal processing unit 21-1 and digital signal processing unit 21-2), and generate a wideband signal based on the independent narrowband signals.

[0026] As shown in FIG. 4, the optical transmitter 2 according to the first embodiment may be composed of two digital signal processing units 21 (21-1, 21-2) each consisting of a signal generating unit 211 and a digital-to-analog conversion unit 214, and a multiplexed signal generating unit 22 consisting of a narrowband signal processing unit 213, a wideband signal generating unit 221, an optical modulation unit 222, and a signal light source 223.

[0027] The signal generator 211-1 of the digital signal processor 21-1 generates a modulated signal sequence (I 1 (n), Q 1 The signal generating unit 211-1 of the digital signal processing unit 21-1 may generate the modulated signal sequence (I 1 (n), Q 1 (n)) may be output to the digital-to-analog conversion section 214-1. Similarly, the signal generator 211-2 of the digital signal processor 21-2 generates a modulated signal sequence (I 2 (n), Q 2 The signal generating unit 211-1 of the digital signal processing unit 21-2 may generate the modulated signal sequence (I 2 (n), Q 2 (n)) may be output to the digital-to-analog conversion section 214-1.

[0028] The digital-to-analog converter 214-1 of the digital signal processor 21-1 may convert the modulated signal sequence input from the signal generator 211-1 into an analog signal. The digital-to-analog converter 214-1 of the digital signal processor 21-1 converts the converted analog signal (I 1 (t), Q1 (t)) may be output to narrowband signal processing section 213. Similarly, the digital-to-analog converter 214-2 of the digital signal processor 21-2 may convert the modulated signal sequence input from the signal generator 211-2 into an analog signal. The digital-to-analog converter 214-2 of the digital signal processor 21-2 converts the converted analog signal (I 2 (t), Q 2 (t)) may be output to narrowband signal processing section 213.

[0029] The narrowband signal processing unit 213 may perform at least one of addition and subtraction processing between narrowband signals, which are analog signals input from the digital-to-analog conversion unit 214-1 of the digital signal processing unit 21-1 and the digital-to-analog conversion unit 214-2 of the digital signal processing unit 21-2, respectively. The narrowband signal processing unit 213 performs at least one of addition and subtraction processing on the narrowband signal ((I 1 ''(t)=I 1 (t)+I 2 (t), Q 1 ''(t)=-Q 1 (t)+Q 2 (t)), (I 2 ''(t)=I 1 (t)-I 2 (t), Q 2 ''(t)=Q 1 (t)+Q 2 (t)) may be output to the wideband signal generating section 221.

[0030] When the optical transmitter 2 has the configuration shown in Fig. 4, the optical transmitter 2 does not need to perform the operation of converting a modulated signal into a narrowband signal (step S2 in the flowchart of Fig. 3). In addition, the optical transmitter 2 shown in Fig. 4 may include three or more digital signal processing units 21.

[0031] 5 is a diagram showing the configuration of an optical receiver 4 according to the first embodiment. The optical receiver 4 includes a semiconductor optical amplifier 41, a multiplexed signal demultiplexer 42, and a digital signal processor 43. The multiplexed signal demultiplexer 42 is realized by an opto-electrical converter 421, a local light source 422, a wideband signal-narrowband signal converter 423, and a narrowband signal processor 424.

[0032] The semiconductor optical amplifier 41 amplifies the intensity of the wideband optical modulated signal received via the transmission line 3. The semiconductor optical amplifier 41 outputs the amplified optical signal to the photoelectric conversion unit 421.

[0033] The photoelectric conversion unit 421 converts the optical signal input from the semiconductor optical amplifier 41 into an electrical signal. The photoelectric conversion unit 421 converts the optical signal into a wideband signal (I(t), Q(t)), which is an analog signal, by interfering the wideband optical modulated signal input from the semiconductor optical amplifier 41 with a local light output from a local light source 422. The photoelectric conversion unit 421 outputs the electrical signal to the wideband signal-narrowband signal conversion unit 423.

[0034] The photoelectric conversion unit 421 includes, for example, a 90-degree optical hybrid, a photodiode, and a transimpedance amplifier (TIA). The photoelectric conversion unit 421 generates interference light from the optical signal input from the semiconductor optical amplifier 41 and local light by, for example, the 90-degree optical hybrid. The in-phase component and quadrature component of the interference light are each input to a photodiode. The current signal generated by the photodiode is converted into a voltage signal by the TIA, and the voltage signal is output to the wideband signal-narrowband signal conversion unit 423.

[0035] The wideband signal-narrowband signal conversion section 423 separates the wideband signal into a plurality of narrowband signals and inputs them to the narrowband signal processing section 424. The narrowband signal processing section 424 performs signal processing between the narrowband signals and outputs them to the digital signal processing section 43.

[0036] Any method can be used to separate the wideband signal into a narrowband signal in the wideband signal-narrowband signal conversion unit 423 and to process the narrowband signals together in the narrowband signal processing unit 424. For example, when the method disclosed in International Publication No. 2019 / 031447 is used, the following processing is performed.

[0037] The wideband signal-narrowband signal conversion unit 423 divides the wideband signal (I(t),Q(t)) input from the photoelectric conversion unit 421 into a plurality of wideband signals (two in this embodiment). The wideband signal-narrowband signal conversion unit 423 frequency-shifts the divided plurality of wideband signals to generate narrowband signals. The wideband signal-narrowband signal conversion unit 423 converts the frequency-shifted plurality of narrowband signals (I 1 '(t),Q 1 '(t)), (I 2 '(t),Q 2 The narrowband signals are respectively output to narrowband signal processing section 424. Each narrowband signal is expressed by (Equation 1).

[0038] (Formula 1) I 1 '(t)=I 1 (t)+I 2 (t), Q 1 '(t)=-Q 1 (t)+Q 2 (t), I 2 '(t)=I 1 (t)-I 2 (t), Q 2 '(t)=Q 1 (t)+Q 2 (t),

[0039] The narrowband signal processing unit 424 performs at least one of addition and subtraction processing on the multiple narrowband signals input from the wideband signal-narrowband signal conversion unit 423. The narrowband signal processing unit 424 outputs the multiple narrowband signals ((I 1 (t), Q 1 (t)), (I2 (t), Q 2 (t)) is output to the analog-to-digital conversion unit 431. The narrowband signal processing unit 424 may be provided in the decoding unit 432 of the digital signal processing unit 43 .

[0040] The digital signal processing unit 43 includes an analog-to-digital conversion unit 431 and a decoding unit 432. The analog-to-digital conversion unit 431 converts the narrowband analog signal sequence input from the multiplexed signal demultiplexing unit 42 into a digital signal sequence ((I 1 (n), Q 1 (n)), (I 2 (n), Q 2 The decoder 432 converts the narrowband signal into a wideband signal, equalizes waveform distortions occurring in the optical transmitter 2, the transmission path 3, and the optical receiver 4, and then decodes the digital signal sequence. Alternatively, the decoding unit 432 may be configured not to convert the narrowband signal into a wideband signal, but to independently equalize waveform distortions that occur in the narrowband signal in the optical transmitter 2, the transmission path 3, and the optical receiver 4, and then decode the digital signal sequence.

[0041] 6 is a flowchart showing the operation of the optical receiver 4 according to the first embodiment. The semiconductor optical amplifier 41 amplifies the wideband optical modulated signal received by the optical receiver 4 with the semiconductor optical amplifier (step S11). The multiplexed signal demultiplexer 42 demultiplexes the wideband optical modulated signal into narrowband signals (step S12). The digital signal processor 43 converts the narrowband analog signal sequence into a digital signal sequence by the analog-digital converter 431, and decodes the narrowband signal by the decoder 432 (step S13).

[0042] In the optical transmission system 1 according to the first embodiment, since the frequency band of the optical signal transmitted by the optical transmitter 2 is wide, it is possible to reduce the influence of nonlinear distortion caused by the semiconductor optical amplifier 23 provided in the optical transmitter 2 and the semiconductor optical amplifier 41 provided in the optical receiver 4.

[0043] The optical receiver 4 according to the first embodiment may have a configuration shown in Fig. 7. As shown in the figure, the optical receiver 4 according to the first embodiment may have a configuration including a plurality of digital signal processing units 43 (digital signal processing unit 43-1 and digital signal processing unit 43-2). The optical receiver 4 may also have a configuration including three or more digital signal processing units.

[0044] Second embodiment FIG. 8 is a diagram showing the configuration of an optical transmitter 2 according to the second embodiment. The optical transmitter 2 according to the second embodiment is characterized in that, unlike the optical transmitter 2 according to the first embodiment, a plurality of optical modulated signals having different center wavelengths are multiplexed in a wavelength multiplexing unit to generate a wideband optical modulated signal. The optical transmitter 2 according to the second embodiment includes a plurality of digital signal processing units 21 (two in this embodiment). The configuration of each digital signal processing unit 21 according to the second embodiment is the same as that of the digital signal processing unit 21 according to the first embodiment, and includes a band dividing unit 212 and a narrowband signal processing unit 213. In this case, the plurality of digital signal processing units 21 may be integrated into one digital signal processing unit 21, and may include the band dividing unit 212 and the narrowband signal processing unit 213. In another embodiment, the plurality of digital signal processing units 21 may include only a signal generating unit 211 and a digital-to-analog converting unit 214, and may perform DA conversion of the I(n) and Q(n) signals without dividing the band. In this case, the multiplexed signal generating unit 22 may not include the broadband signal generating unit 221, and may optically modulate and wavelength-multiplex a plurality of analog narrowband signals output from the plurality of digital signal processing units 21. In this case, the optical transmitter 2 may be configured to integrate a plurality of digital signal processing units 21 into one digital signal processing unit 21, and may include only the signal generating unit 211 and the digital-analog converting unit 214 to output a plurality of narrowband signals.

[0045] The multiplexed signal generating unit 22 according to the second embodiment includes a broadband signal generating unit 221, an optical modulating unit 222, and a plurality of signal light sources 223 (two in this embodiment), and also includes a wavelength multiplexing unit 224. Moreover, the optical transmitter 2 according to the second embodiment does not include a plurality of signal light sources 223, and the signal light source 223 may be a supercontinuum light source having a plurality of optical carrier waves, and these carrier waves may be divided to output signal light to a plurality of optical modulating units 222.

[0046] The optical modulation unit 222 according to the second embodiment modulates each of the analog signal sequences input from the digital signal processing unit 21 to generate optically modulated signals. The optical modulation unit 222 according to the second embodiment outputs the optically modulated signals to a wavelength multiplexing unit 224.

[0047] The wavelength multiplexer 224 multiplexes the optically modulated signals input from the multiple optical modulators 222 to generate a wideband optically modulated signal. The frequency band of the wideband optically modulated signal is wider than the frequency band of the optically modulated signal. The wavelength multiplexer 224 outputs the wideband optically modulated signal to the semiconductor optical amplifier 23.

[0048] The semiconductor optical amplifier 23 according to the second embodiment amplifies the intensity of the wideband optical modulated signal input from the wavelength multiplexer 224. The semiconductor optical amplifier 23 according to the second embodiment outputs the amplified optical signal to the optical receiver 4 via the transmission path 3.

[0049] 9 is a flowchart showing the operation of the optical transmitter 2 according to the second embodiment. The signal generating unit 211 generates a modulated signal (step S21). The band dividing unit 212 converts the modulated signal into a narrowband signal (step S22). The broadband signal generating unit 221 generates a broadband signal based on a plurality of narrowband signals (step S23). The wavelength multiplexing unit 224 multiplexes a plurality of optical modulated signals output from the optical modulating unit 222 to generate a broadband optical modulated signal (step S24). The semiconductor optical amplifier 23 amplifies the broadband optical modulated signal (step S25). As described above, if the digital signal processing unit 21 includes only the signal generating unit 211 and the digital-to-analog converting unit 214 and the multiplexed signal generating unit 22 does not include the wideband signal generating unit 221, step S22 can be omitted.

[0050] The optical transmitter 2 according to the second embodiment can generate an optical signal with a wide band by multiplexing optical modulated signals using the wavelength multiplexing unit 224. Therefore, the fluctuation time of the optical modulated signal handled by the optical transmitter 2 according to the second embodiment is shorter than the carrier lifetime of the semiconductor optical amplifier, similar to the optical transmitter 2 according to the first embodiment. Therefore, the optical transmitter 2 according to the second embodiment can reduce the influence of nonlinear distortion caused by the semiconductor optical amplifier.

[0051] FIG. 10 is a diagram showing a configuration of an optical receiver 4 according to the second embodiment. The optical receiver 4 according to the second embodiment is characterized in that, unlike the optical receiver 4 according to the first embodiment, a wideband optical modulated signal is demultiplexed by a wavelength demultiplexing unit 425 to generate a narrowband signal. The optical receiver 4 according to the second embodiment includes a semiconductor optical amplifier 41, a multiplexed signal demultiplexing unit 42, and a plurality of (two in this embodiment) digital signal processing units 43. The multiplexed signal demultiplexing unit 42 includes a wavelength demultiplexing unit 425, a plurality of (two in this embodiment) photoelectric conversion units 421, a local light source 422, a wideband signal-narrowband signal conversion unit 423, and a narrowband signal processing unit 424. Each digital signal processing unit 43 according to the second embodiment has the same configuration as the digital signal processing unit 43 according to the first embodiment, and includes an analog-digital conversion unit 431 and a decoding unit 432. In another embodiment, the multiplexed signal separation unit 42 may include only the wavelength demultiplexing unit 425, the photoelectric conversion unit 421, and the local light source 422, and may output I(t) and Q(t) signals without converting the analog signal into a narrowband signal. In this case, the optical receiver 4 may include one digital signal processing unit 43, and may perform AD conversion and decode the signal input from the photoelectric conversion unit 421. Furthermore, the optical receiver 4 according to the second embodiment may not include a plurality of local light sources 422, and the local light source 422 may be a supercontinuum light source having a plurality of optical carriers, and these carriers may be divided to output local light to a plurality of photoelectric conversion units 421.

[0052] The wavelength demultiplexing unit 425 demultiplexes the broadband optical modulated signal input from the semiconductor optical amplifier 41. The wavelength demultiplexing unit 425 outputs the demultiplexed optical signals to the corresponding photoelectric conversion units 421, respectively.

[0053] The photoelectric conversion unit 421 according to the second embodiment converts an optical signal input from the wavelength demultiplexing unit 425 into an electrical signal. The wideband signal-narrowband signal conversion unit 423 according to the second embodiment separates the wideband signal input from the photoelectric conversion unit 421 into a plurality of narrowband signals and inputs them to the narrowband signal processing unit 424. The narrowband signal processing unit 424 according to the second embodiment performs at least one of addition and subtraction processing between the plurality of narrowband signals input from the wideband signal-narrowband signal conversion unit 423. The analog-digital conversion unit 431 according to the second embodiment converts the narrowband analog signal sequence input from the multiplexed signal demultiplexing unit 42 into a digital signal sequence. The decoding unit 432 according to the second embodiment converts the narrowband signal into a wideband signal, equalizes waveform distortions occurring in the optical transmitter 2, the transmission path 3, and the optical receiver 4, and then decodes the digital signal sequence.

[0054] 11 is a flowchart showing the operation of the optical receiver 4 according to the second embodiment. The semiconductor optical amplifier 41 amplifies the wideband optical modulated signal received by the optical receiver 4 (step S31). The wavelength demultiplexing unit 425 included in the multiplexed signal demultiplexing unit 42 demultiplexes the wideband optical modulated signal and separates it into narrowband signals (step S32). The digital signal processing unit 43 converts the narrowband analog signal sequence into a digital signal sequence by the analog-digital conversion unit 431, and decodes the narrowband signal by the decoding unit 432 (step S33).

[0055] Like the optical transmission system 1 according to the first embodiment, the optical transmission system 1 according to the second embodiment can reduce the effects of nonlinear distortion caused by the semiconductor optical amplifier 23 provided in the optical transmitter 2 and the semiconductor optical amplifier 41 provided in the optical receiver 4 because the frequency band of the optical signal transmitted by the optical transmitter 2 is wide.

[0056] Third embodiment FIG. 12 is a diagram showing the configuration of the digital signal processing unit 21 and the digital signal processing unit 43 according to the third embodiment. The digital signal processing unit 21 according to the third embodiment is different from the digital signal processing unit 21 according to the first embodiment or the second embodiment in that the digital signal processing unit 21 includes an SOA distortion compensation unit 215. The digital signal processing unit 43 according to the third embodiment is different from the digital signal processing unit 43 according to the first embodiment or the second embodiment in that the digital signal processing unit 43 includes an SOA distortion estimation unit 434 and a physical parameter estimation unit 435. If the physical parameters are known, the digital signal processing unit 43 according to the third embodiment may not include the SOA distortion estimation unit 434 and the physical parameter estimation unit 435. Any method can be used for the SOA distortion compensation unit 215, the SOA distortion estimation unit 434, and the physical parameter estimation unit 435. For example, the method described in JP 2018-019255 A can be used to compensate for distortion caused by SOA as follows.

[0057] The SOA distortion compensating unit 215 compensates for distortion caused by the semiconductor optical amplifier 23, for the modulated signal generated by the signal generating unit 211. The SOA distortion compensating unit 215 outputs the compensated signal to the band dividing unit 212.

[0058] The SOA distortion compensation unit 215 acquires estimates of the physical parameters of the semiconductor optical amplifier 23 from the physical parameter estimation unit 435 of the optical receiver 4. The SOA distortion compensation unit 215 estimates nonlinear signal distortion occurring in the optical signal input to the semiconductor optical amplifier 23 based on the estimates of the physical parameters of the semiconductor optical amplifier 23, and compensates for the nonlinear signal distortion. Note that, if the physical parameters are known, the physical parameters can be set in the SOA distortion compensation unit 215 in advance.

[0059] The SOA distortion compensation unit 215 calculates a gain coefficient h(t) of a nonlinear signal distortion occurring in an optical signal input to the semiconductor optical amplifier 23 by the semiconductor optical amplifier 23, based on an estimated value of a physical parameter of the semiconductor optical amplifier 23. The SOA distortion compensation unit 215 calculates a value (exp((-h(t)(1+jα)) / 2)) representing the inverse characteristic of the gain coefficient h(t) of the nonlinear signal distortion, using a gain coefficient -h(t) having the inverse characteristic of the gain coefficient h(t) of the nonlinear signal distortion. The SOA distortion compensation unit 215 multiplies the optical signal input to the semiconductor optical amplifier 23 by the value (exp((-h(t)(1+jα)) / 2)) representing the inverse characteristic of the gain coefficient h(t) of the nonlinear signal distortion. In this way, the SOA distortion compensation unit 215 can pre-equalize the nonlinear signal distortion occurring in the optical signal input to the semiconductor optical amplifier 23.

[0060] The relationship between the optical signal acquired by the semiconductor optical amplifier 23 and the optical signal output by the semiconductor optical amplifier 23 is expressed by a physical model shown in equation (1) (see Non-Patent Documents 3 and 4).

[0061]

number

[0062] Here, E I (t) denotes the complex amplitude of the optical signal acquired by the semiconductor optical amplifier 23 (the optically modulated signal output by the optical modulation unit 222). o (t) denotes the complex amplitude of the optical signal transmitted by the semiconductor optical amplifier 23. h(t) denotes the gain coefficient. α denotes the linewidth enhancement factor. j denotes the imaginary unit. exp(h(t)(1+jα) / 2) denotes the nonlinear signal distortion caused in the optical modulated signal by the semiconductor optical amplifier 23.

[0063] In the physical model shown in equation (1), the gain coefficient h(t) is expressed by the differential equation shown in equation (2).

[0064]

number

[0065] Here, τ c h denotes the carrier lifetime. 0 denotes the non-saturation gain. P sat indicates the saturated output. These, together with the linewidth enhancement factor α shown in equation (1), are physical parameters of the semiconductor optical amplifier 23. In the physical model shown in equation (1), if these physical parameters are determined, the behavior of the nonlinear signal distortion caused in the transmission signal by the semiconductor optical amplifier 23 can be expressed.

[0066] Equation (2) shows that the time change of the gain coefficient h(t) depends on the power of the optical signal acquired by the semiconductor optical amplifier 23. Therefore, if the physical parameters of the semiconductor optical amplifier 23 are known, the gain coefficient h(t) that depends on the power of the optical signal can be obtained from equation (2).

[0067] The SOA distortion compensation unit 215 can obtain the gain coefficient h(t) as a numerical solution from equation (2) by, for example, a time evolution solution using the Euler method or the Nth-order (N is a positive integer) Runge-Kutta method. When obtaining the gain coefficient h(t) from equation (2), the SOA distortion compensation unit 215 may use an analytical solution if one exists.

[0068] The SOA distortion compensation unit 215 uses a gain coefficient (-h(t)) having the inverse characteristic of the gain coefficient h(t) to calculate a value (exp(-h(t)(1+jα) / 2)) representing the inverse characteristic of the gain coefficient h(t) of the nonlinear signal distortion.

[0069] The SOA distortion compensator 215 outputs a value (exp(-h(t)(1+jα) / 2)) representing the inverse characteristic of the gain coefficient h(t) of the nonlinear signal distortion to the optical modulated signal E I By multiplying it by (t), the SOA distortion compensator 215 compensates for the nonlinear signal distortion occurring in the optically modulated signal by the semiconductor optical amplifier 23. In this way, the SOA distortion compensator 215 can pre-equalize the nonlinear signal distortion occurring in the optically modulated signal by the semiconductor optical amplifier 23.

[0070] The SOA distortion compensator 215 may obtain the gain coefficient h(t) from equation (2) by a solution other than the time evolution solution. When the physical parameters of the semiconductor optical amplifier 23 are not estimated, the SOA distortion compensator 215 may set the gain coefficient h(t) to 0 and may not compensate for the nonlinear signal distortion occurring in the optical modulated signal in the semiconductor optical amplifier 23. When the physical parameters of the semiconductor optical amplifier 23 are not estimated, the modulated signal output from the signal generator 211 may bypass the SOA distortion compensator 215 and may not compensate for the nonlinear signal distortion occurring in the optical modulated signal in the semiconductor optical amplifier 23.

[0071] The SOA distortion estimation unit 434 acquires a received signal, which is a digital signal based on a transmission signal of the optical transmitter 2, from the analog-digital conversion unit 431. The SOA distortion estimation unit 434 acquires the transmission signal of the optical transmitter 2 as a reference signal from the optical transmitter 2. For example, the SOA distortion estimation unit 434 acquires the transmission signal of the optical transmitter 2 as a reference signal from the optical transmitter 2 via a control channel 5, which is a communication channel (see Non-Patent Document 5), a NE-OpS (Network Element-Operations Systems), a NW-OpS (Network-Operations System), or the like. For example, the SOA distortion estimation unit 434 acquires a known signal, which is a part of a transmission data sequence, as a reference signal from the optical transmitter 2. For example, the SOA distortion estimation unit 434 acquires a series of symbol values ​​of a received signal as a reference signal from the optical transmitter 2.

[0072] The SOA distortion estimation unit 434 estimates the measured optical signal E o (t) is the optical signal E I Based on the result of division by (t) and equation (1), a value (exp(h(t)(1+jα) / 2)) representing the nonlinear signal distortion caused in the transmission signal by the semiconductor optical amplifier 23 and the linewidth enhancement factor α are calculated as shown in equation (3).

[0073]

number

[0074] The SOA distortion estimation unit 434 may calculate the average value of the same symbol by using the reference signal as a repetitive signal. This allows the SOA distortion estimation unit 434 to reduce signal distortion caused by white noise. The SOA distortion estimation unit 434 can improve the estimation accuracy of nonlinear signal distortion.

[0075] When the nonlinear signal distortion caused by the semiconductor optical amplifier 23 is large, the SOA distortion estimation unit 434 may not be able to accurately estimate the nonlinear signal distortion due to degradation of signal quality. The SOA distortion estimation unit 434 may repeat the estimation by feeding back a value estimated once. This allows the SOA distortion estimation unit 434 to compensate the transfer function with higher accuracy even when the nonlinear signal distortion caused by the semiconductor optical amplifier 23 is large.

[0076] The measured values ​​of the physical parameters of the semiconductor optical amplifier 23 may differ from the design values ​​of the physical parameters of the semiconductor optical amplifier 23 due to individual differences caused by manufacturing errors of the semiconductor optical amplifier 23, etc. Therefore, the physical parameter estimation unit 435 estimates the physical parameters of the semiconductor optical amplifier 23 by digital signal processing. This allows the SOA distortion compensation unit 215 of the optical transmitter 2 to absorb the individual differences of the semiconductor optical amplifier 23 of the optical transmitter 2 and compensate for the nonlinear signal distortion. The SOA distortion estimation unit 434 can compensate for the nonlinear signal distortion even for the semiconductor optical amplifier 23 having unknown physical parameters. The physical parameter estimation unit 435 estimates the physical parameters of the semiconductor optical amplifier 23 based on the result of the SOA distortion estimation unit 434 estimating the nonlinear signal distortion based on the reference signal.

[0077] The physical parameter estimation unit 435 estimates the physical parameters of the semiconductor optical amplifier 23 using the gain coefficient h(t) calculated using equation (3) and equation (2). The physical parameters of the semiconductor optical amplifier 23 include, for example, the carrier lifetime τ c , unsaturated gain h 0 , saturated output P sat It is.

[0078] There is no particular limitation to the method used by the physical parameter estimation unit 435 to estimate the physical parameters of the semiconductor optical amplifier 23. For example, the physical parameter estimation unit 435 may estimate the physical parameters of the semiconductor optical amplifier 23 by fitting using a least squares method, calculation using simultaneous equations, or the like.

[0079] The physical parameter estimating unit 435 feeds back the physical parameters of the semiconductor optical amplifier 23 to the SOA distortion compensating unit 215 via a control channel 5 such as a communication channel (see Non-Patent Document 5) or NE-OpS or NW-OpS.

[0080] In addition, when the optical transmitter 2 and the optical receiver 4 are directly connected by a dedicated line, the physical parameter estimation unit 435 may estimate the physical parameters of the semiconductor optical amplifier 23 based on the optical signal transmitted through the dedicated line instead of the transmission line 3. After estimating the physical parameters of the semiconductor optical amplifier 23, the physical parameter estimation unit 435 can transmit to the optical transmitter 2 and the decoding unit 432 a signal resulting from removing the reference signal from the transmission signal to which the reference signal has been added. If it is necessary to estimate the physical parameters again after this, the physical parameter estimation unit 435 may add the reference signal again to the transmission signal. When the current injected into the semiconductor optical amplifier 23 does not change or when the intensity of the optical signal acquired by the semiconductor optical amplifier 23 does not change, the physical parameter estimation unit 435 can continuously use the estimation result of the physical parameters of the semiconductor optical amplifier 23. In these cases, the physical parameter estimation unit 435 may suspend the estimation of the physical parameters of the semiconductor optical amplifier 23, or may continuously and periodically calculate the physical parameters of the semiconductor optical amplifier 23. The physical parameter estimation unit 435 recalculates the physical parameters of the semiconductor optical amplifier 23 when the current injected into the semiconductor optical amplifier 23 does not change or when the intensity of the optical signal acquired by the semiconductor optical amplifier 23 changes.

[0081] As described above, the optical transmitter 2 according to the third embodiment can compensate for distortion caused by the semiconductor optical amplifier 23 in the modulated signal generated by the signal generating unit 211, and can further reduce the effects of nonlinear distortion caused by the semiconductor optical amplifier.

[0082] The SOA distortion estimation unit 434 and the physical parameter estimation unit 435 are not limited to be provided in the digital signal processing unit 43. For example, the physical parameter estimation unit 435 or both the SOA distortion estimation unit 434 and the physical parameter estimation unit 435 may be provided in the corresponding digital signal processing unit 21, and the digital signal processing unit 43 and the digital signal processing unit 21 may transmit and receive signals through the control channel 5.

[0083] Moreover, the SOA distortion compensation unit is not limited to be provided in the digital signal processing unit 21. For example, the decoding unit 432 of the digital signal processing unit 43 may be provided with an SOA distortion compensation unit, and the nonlinear signal distortion occurring in the transmission signal in the semiconductor optical amplifier 23 may be compensated for by multiplying the signal converted by the analog-to-digital conversion unit 431 by a value (exp(-h(t)(1+jα) / 2)) representing the inverse characteristic of the gain coefficient h(t) of the nonlinear signal distortion.

[0084] The SOA distortion compensation unit 215 and the SOA distortion compensation unit provided in the decoding unit 432 may compensate for the nonlinear signal distortion caused by the semiconductor optical amplifier 41 provided in the optical receiver 4 in the same way as the nonlinear signal distortion caused by the semiconductor optical amplifier 23.

[0085] <Experimental Example> An experimental example in the configuration of Fig. 2 of the first embodiment will be described below. In the experimental example, the symbol rates of the wideband optical modulated signal input from the optical modulation unit 222 of the optical transmitter 2 to the semiconductor optical amplifier 23 are 42GBd, 84GBd, and 168GBd. The modulation method is polarization multiplexed 16QAM (quadrature amplitude modulation) with probabilistic constellation shaping. In addition, the current injected into the semiconductor optical amplifier 23 was changed to change the amplification factor.

[0086] Fig. 13 is a table showing signal space diagrams under each condition. The six signal space diagrams shown in Fig. 13 are signal space diagrams showing signals output from the optical transmitter 2 when the current injected into the semiconductor optical amplifier 23 is 100 mA and 350 mA, and the symbol rate of the wideband optical modulated signal is 42 GBd, 84 GBd, and 168 GBd. It was confirmed that by increasing the symbol rate of the optical modulated signal from 42 GBd to 84 GBd and from 84 GBd to 168 GBd, the boundaries between signal points became clearer and nonlinear distortion caused by the semiconductor optical amplifier was reduced, especially when the injection current was 350 mA.

[0087] In addition, the dependence of the injection current to the semiconductor optical amplifier on the difference between the SNR of the optical signal output from the semiconductor optical amplifier 23 of the optical transmitter 2 and the SNR of the optical signal output from the EDFA when the semiconductor optical amplifier 23 of the optical transmitter is replaced with an EDFA (Erbium Doped Fiber Amplifier) ​​is shown as the SNR penalty.

[0088] Figure 14 is a graph showing the relationship between the magnitude of the injection current (SOA injection current) into the semiconductor optical amplifier and the SNR penalty. When the SOA injection current was 350 mA, the SNR penalty for an optical modulated signal with a symbol rate of 168 GBd was approximately 2 dB smaller than the SNR penalty for a symbol rate of 42 GBd, and approximately 1 dB smaller than the SNR penalty for a symbol rate of 84 GBd. This shows that the use of an optical modulated signal with a high symbol rate reduces nonlinear distortion caused by the semiconductor optical amplifier, especially when the amplification factor of the semiconductor optical amplifier is high.

[0089] Other Embodiments Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to the above, and various design changes, etc. are possible within the scope that does not deviate from the gist of the present invention.

[0090] In the above embodiment, the signal generating unit 211 generates a modulated signal sequence (I(n), Q(n)) which is an electrical signal indicating the in-phase and quadrature components of an optical signal, but is not limited to this. For example, the signal generating unit 211 may generate electrical signals (XI(n), XQ(n), YI(n), YQ(n)) indicating the in-phase and quadrature components of the X-polarized and Y-polarized optical signal by utilizing the polarization of the optical signal.

[0091] In the first embodiment, the semiconductor optical amplifier 23 of the optical transmitter 2 amplifies the intensity of the optically modulated signal generated by the optical modulation unit 222, but is not limited to this. The semiconductor optical amplifier 23 may be provided between the optical modulation unit 222 and the signal light source 223, and may amplify the signal light input from the signal light source 223 and output it to the optical modulation unit 222. Furthermore, when the optical signal has different signals in the X polarization and the Y polarization, the semiconductor optical amplifier 23 may be included in the optical modulation unit 222 and may amplify only one of the X polarization component or the Y polarization component, or a plurality of semiconductor optical amplifiers 23 may be included in the optical modulation unit 222 and may amplify both.

[0092] In the first embodiment, the semiconductor optical amplifier 41 of the optical receiver 4 amplifies the intensity of the optical signal input to the optical receiver 4, but is not limited to this. When the optical signal has different signals in the X polarization and the Y polarization, the semiconductor optical amplifier 41 may be included in the photoelectric conversion unit 421 and may amplify only the X polarization component or the Y polarization component, or a plurality of semiconductor optical amplifiers 41 may be included in the photoelectric conversion unit 421 and may amplify both.

[0093] The optical transmitter 2 and the optical receiver 4 may be realized by the same device. In this case, the signal light source 223 and the local light source 422 may be the same light source.

[0094] Although the first and second embodiments are configuration examples in which an IQ modulated signal is handled, a configuration example in which an intensity modulated signal is handled may be used. In this case, the 90-degree optical hybrid constituting the local light source 422 and the photoelectric conversion unit 421 can be omitted.

[0095] 15 is a diagram showing an optical transceiver 100 according to this embodiment. The optical transceiver 100 includes a processing device 101 and an optical front-end 102. The processing device 101 includes a digital signal processing device 21 and a digital signal processing device 43. The optical front-end 102 includes a multiplexed signal generating device 22, a semiconductor optical amplifier 23, a semiconductor optical amplifier 41, and a multiplexed signal demultiplexing device 42. The multiplexed signal generating device 22, the semiconductor optical amplifier 23, the semiconductor optical amplifier 41, and the multiplexed signal demultiplexing device 42 that configure the optical front-end 102 may be integrated. The signal light source 223 may be integrated in the optical front-end 102. The multiplexed signal demultiplexing device 42 may not include a local light source 422, and may have the function of the local light source 422 by branching the signal light source 223.

[0096] As described above, the optical transceiver 100 may perform communication using electrical signals (XI(n), XQ(n), YI(n), YQ(n)) indicating the in-phase and quadrature components of the X and Y polarizations of the optical signal by utilizing the polarization of the optical signal. Fig. 16 is a diagram showing an optical transceiver 100 performing polarization multiplexing according to this embodiment. 16, in digital signal processing unit 21, signal generation unit 211 generates electrical signals (XI(n), XQ(n), YI(n), YQ(n)) indicating in-phase and quadrature components of X polarization and Y polarization of an optical signal, and band division unit 212, narrowband signal processing unit 213, and digital-to-analog conversion unit 214 process the electrical signals related to the X polarization and the Y polarization independently. In multiplexed signal generation unit 22, wideband signal generation unit 221 processes the electrical signals related to the X polarization and the Y polarization independently, and optical modulation unit 222 generates an optical signal by performing polarization synthesis in addition to optical modulation.

[0097] In the multiplexed signal separation unit 42, the photoelectric conversion unit 421 performs photoelectric conversion after performing polarization separation of the optical signal to generate wideband signals related to the X polarization and the Y polarization. The wideband signal-narrowband signal conversion unit 423, the narrowband signal processing unit 424, and the analog-to-digital conversion unit 431 process the electric signal related to the X polarization and the electric signal related to the Y polarization independently. The decoding unit 432 decodes the electric signal related to the X polarization and the electric signal related to the Y polarization to generate a received data series. The multiplexed signal generating unit 22, the semiconductor optical amplifier 23, the semiconductor optical amplifier 41, and the multiplexed signal demultiplexing unit 42 may be integrated into an optical front end 102. A signal light source 223 may be integrated into the optical front end 102. [Explanation of symbols]

[0098] 1 Optical transmission system, 2 Optical transmitter, 3 Transmission path, 4 Optical receiver, 21 Digital signal processing unit, 211 Signal generation unit, 212 Band division unit, 213 Narrowband signal processing unit, 214 Digital-to-analog conversion unit, 22 Multiplexed signal generation unit, 221 Broadband signal generation unit, 222 Optical modulation unit, 223 Signal light source, 224 Wavelength multiplexing unit, 23, 41 Semiconductor optical amplifier, 42 Multiplexed signal separation unit, 421 Photoelectric conversion unit, 422 Local light source, 423 Broadband signal-narrowband signal conversion unit, 424 Narrowband signal processing unit, 425 Wavelength demultiplexing unit

Claims

1. a multiplexed signal generating unit that multiplexes a plurality of narrowband signals to generate a broadband optical modulated signal; a semiconductor optical amplifier for amplifying the intensity of the broadband optical modulated signal; Equipped with a difference between a fluctuation time of the wideband optical modulated signal and a carrier lifetime of the semiconductor optical amplifier is larger than a difference between a fluctuation time of a narrowband optical modulated signal generated by modulating the narrowband signal and the carrier lifetime. Optical transmitter.

2. The multiplexed signal generation unit includes: a wideband signal generating unit that generates, from the plurality of narrowband signals, a wideband signal having a wider frequency band than the narrowband signals; an optical modulation unit that modulates an optical signal based on the wideband signal to generate the wideband optical modulated signal; The optical transmitter of claim 1 .

3. The multiplexed signal generation unit includes: a plurality of optical modulation units that modulate optical signals based on the narrowband signals to generate optically modulated signals; a wavelength multiplexing unit that multiplexes a plurality of the optical modulated signals to generate the wideband optical modulated signal; The optical transmitter of claim 1 .

4. a distortion compensator that compensates for distortion of the wideband optical modulated signal caused by the semiconductor optical amplifier; The optical transmitter according to claim 1 , further comprising:

5. a semiconductor optical amplifier for amplifying the intensity of a broadband optical modulated signal; a multiplexed signal separator that separates the broadband optical modulated signal into narrowband signals; Equipped with a difference between a fluctuation time of the wideband optical modulated signal and a carrier lifetime of the semiconductor optical amplifier is larger than a difference between a fluctuation time of a narrowband optical modulated signal generated by modulating the narrowband signal and the carrier lifetime. Optical receiver.

6. The multiplexed signal separation unit includes: an opto-electrical conversion unit that converts the amplified broadband optical modulated signal into an electrical signal; a wideband signal-narrowband signal conversion unit that separates the electrical signal based on a band; 6. The optical receiver of claim 5, comprising:

7. The multiplexed signal separation unit includes: a wavelength demultiplexing unit that demultiplexes the amplified broadband optical modulated signal and generates a narrowband optical modulated signal; an opto-electrical conversion unit that converts the narrowband optical modulated signal into a narrowband signal; 6. The optical receiver of claim 5, comprising:

8. an SOA distortion compensator that compensates for distortion of the wideband optical modulated signal caused by the semiconductor optical amplifier; 8. The optical receiver according to claim 6 or 7, further comprising:

9. a multiplexed signal generating step of multiplexing a plurality of narrowband signals to generate a wideband optical modulated signal; a semiconductor optical amplifier step of amplifying the intensity of the broadband optical modulated signal; having a difference between a fluctuation time of the wideband optical modulated signal and a carrier lifetime in the semiconductor optical amplification step is larger than a difference between a fluctuation time of a narrowband optical modulated signal generated by modulating the narrowband signal and the carrier lifetime. Optical transmission method.

10. a semiconductor optical amplifier step of amplifying the intensity of the broadband optical modulated signal; a multiplexing signal demultiplexing step of demultiplexing the broadband optical modulated signal into narrowband signals; a difference between a fluctuation time of the wideband optical modulated signal and a carrier lifetime in the semiconductor optical amplification step is larger than a difference between a fluctuation time of a narrowband optical modulated signal generated by modulating the narrowband signal and the carrier lifetime. An optical receiving method comprising:

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