Abstract: There is provided a communication system, wherein: an optical transmission apparatus has: a first storage unit that stores amplitude distribution information, which is information representing a distribution of occurrence probabilities of symbols of an optical signal, in association with a modulation rate of an optical signal; a control unit that selects the modulation rate based on a signal band that is a band determined by the modulation rate and a device band that is a band in which a transmission path and the like allow passage of an optical signal, and controls an occurrence probability of a symbol of an optical signal based on the amplitude distribution information; and an optical transmitter that transmits an optical signal of a symbol of which the occurrence probability is controlled; and an optical reception apparatus has: an optical receiver that receives an optical signal of a symbol; a second storage unit that stores the amplitude distribution information in association with the modulation rate; a

Abstract: An optical transmitter includes a first narrowband signal processing unit, a wideband signal generation unit, and an optical modulator. The first narrowband signal generation unit is configured to input a first signal and a second signal and output first, second, third and fourth narrowband signals. The wideband signal generation unit is configured to multiply the first and second narrowband signals by sinusoidal signals having a phase difference of (?/2), respectively, to shift bands of the first and second narrowband signals, and combine the shifted first and second narrowband signal to generate a first wideband signal. The wideband signal generation unit is configured to multiply the third and fourth narrowband signal by sinusoidal signals having a phase difference of (?/2), respectively, to shift bands of the third and fourth narrowband signals, and combine the shifted third and fourth narrowband signals to generate a second wideband signal.

Abstract: A digital coherent receiver includes: an adaptive equalizer configured to execute, using a first tap coefficient, adaptive equalization processing on a digital signal that corresponds to a signal; a first coefficient updating unit configured to update the first tap coefficient based on the digital signal on which the adaptive equalization processing has not been executed, the digital signal on which the adaptive equalization processing has been executed, and a first step size; a second coefficient updating unit configured to update a second tap coefficient based on the digital signal on which the adaptive equalization processing has not been executed, the digital signal on which the adaptive equalization processing has been executed, and a second step size; and a control unit configured to detect a fluctuation speed of a state of polarization of the digital signal based on the second tap coefficient, and change the first tap coefficient to the updated second tap coefficient if it is determined that the fluctu

Abstract: An optical transmission system includes an optical transmitter, an optical receiver, and a control apparatus. The control apparatus repeatedly performs an adjustment process for adjusting power of an optical signal of a frequency band to be adjusted while switching the frequency band to be adjusted between at least two frequency bands including at least a frequency band where stimulated Raman scattering occurs among frequency bands that are multiplexed in a multiplexed optical signal transmitted by the optical transmission system. In the adjustment process, when power of an optical signal of the frequency band to be adjusted transmitted from the optical transmitter has been changed, the control apparatus determines the power of the optical signal of the frequency band to be adjusted on the basis of a signal quality measured by the optical receiver that has received the optical signal.

Abstract: An optical receiver that demodulates an optical modulation signal into a baseband signal, which is an electrical signal, and decodes a received symbol acquired by converting the baseband signal. The optical receiver includes: an analog-to-digital converter that converts the baseband signal into a digital signal of which the number of samples per received symbol is M/N (samples/symbol), M and N being positive integers, M/N being not an integer, and “M>N” being satisfied; and an adaptive equalization processing unit that executes an equalization operation set in advance to output the received symbol on the basis of the digital signal of which the number of samples per received symbol is M/N (samples/symbol) and a predetermined tap coefficient digital signal equalization tap coefficients used for equalization of a signal, the coefficient being updated in any sampling period.

Abstract: An optical transmitter includes a first narrowband signal processing unit, a wideband signal generation unit, and an optical modulator. The first narrowband signal generation unit is configured to input a first signal and a second signal and output first, second, third and fourth narrowband signals. The wideband signal generation unit is configured to multiply the first and second narrowband signals by sinusoidal signals having a phase difference of (?/2), respectively, to shift bands of the first and second narrowband signals, and combine the shifted first and second narrowband signal to generate a first wideband signal. The wideband signal generation unit is configured to multiply the third and fourth narrowband signal by sinusoidal signals having a phase difference of (?/2), respectively, to shift bands of the third and fourth narrowband signals, and combine the shifted third and fourth narrowband signals to generate a second wideband signal.

Abstract: An optical transmitter of an optical data transmission system transmitting data through an optical fiber transmission path includes a main signal generator that converts first transmission data into a predetermined signal format to generate a first signal, a DCSK modulator that DCSK-modulates second transmission data to generate a second signal, a signal-multiplexer that performs time-division multiplexing of the first signal and the second signal, and an electro-optical converter that converts a multiplexed signal obtained by the time-division multiplexing of the signal-multiplexer from an electric signal into an optical signal, and outputs the optical signal to the optical fiber transmission path.

Abstract: An optical receiver that demodulates an optical modulation signal into a baseband signal, which is an electrical signal, and decodes a received symbol acquired by converting the baseband signal. The optical receiver includes: an analog-to-digital converter that converts the baseband signal into a digital signal of which the number of samples per received symbol is M/N (samples/symbol), M and N being positive integers, M/N being not an integer, and “M >N” being satisfied; and an adaptive equalization processing unit that executes an equalization operation set in advance to output the received symbol on the basis of the digital signal of which the number of samples per received symbol is M/N (samples/symbol) and a predetermined tap coefficient digital signal equalization tap coefficients used for equalization of a signal, the coefficient being updated in any sampling period.

Abstract: An optical transmitter of an optical data transmission system transmitting data through an optical fiber transmission path includes a main signal generator that converts first transmission data into a predetermined signal format to generate a first signal, a DCSK modulator that DCSK-modulates second transmission data to generate a second signal, a signal-multiplexer that performs time-division multiplexing of the first signal and the second signal, and an electro-optical converter that converts a multiplexed signal obtained by the time-division multiplexing of the signal-multiplexer from an electric signal into an optical signal, and outputs the optical signal to the optical fiber transmission path.

Abstract: A digital signal processor which performs digital signal processing of a digital signal includes a statistical analysis method which calculates a moving average and a standard deviation from the digital signal, performs statistical decision deciding whether or not the digital signal is within a predetermined range obtained from the moving average and the standard deviation, and corrects the digital signal outside the range within the range. Statistical analysis of the digital signal is performed, thereby suppressing transient changes without increasing the number of times of averaging during the digital signal processing.

Abstract: A receiver is configured to have two coherent receivers using two pieces of local oscillator of optical frequencies f11 and f12 close to optical frequency f1 of signal light, the two pieces of local oscillator being controlled to have a predetermined optical frequency spacing ?F, and a digital signal processor demodulating transmission data signal sequences based on outputs from the coherent receivers. When the frequency difference ?f1 of one of the two pieces of local oscillator from a virtual reference frequency f1? close to the optical frequency f1 of the signal light is set, the digital signal processor obtains the frequency difference ?f2 of the other of the two pieces of local oscillator by calculating ?f1??F, inputs electric signals output from the two coherent receivers, and compensates the phase rotation caused in the electric signals by frequency differences ?f1 and ?f2.

Abstract: A receiver is configured to have two coherent receivers using two pieces of local oscillator of optical frequencies f11 and f12 close to optical frequency f1 of signal light, the two pieces of local oscillator being controlled to have a predetermined optical frequency spacing ?F, and a digital signal processor demodulating transmission data signal sequences based on outputs from the coherent receivers. When the frequency difference ?f1 of one of the two pieces of local oscillator from a virtual reference frequency f1? close to the optical frequency f1 of the signal light is set, the digital signal processor obtains the frequency difference ?f2 of the other of the two pieces of local oscillator by calculating ?f1-?F, inputs electric signals output from the two coherent receivers, and compensates the phase rotation caused in the electric signals by frequency differences ?f1 and ?f2.

Abstract: A digital signal processor which performs digital signal processing of a digital signal includes a statistical analysis method which calculates a moving average and a standard deviation from the digital signal, performs statistical decision deciding whether or not the digital signal is within a predetermined range obtained from the moving average and the standard deviation, and corrects the digital signal outside the range within the range. Statistical analysis of the digital signal is performed, thereby suppressing transient changes without increasing the number of times of averaging during the digital signal processing.