Abstract: A signal processing device processes an electric field information signal indicating a polarization multiplexed optical signal in which different modulation formats are used. A first optical signal transmitted in a first polarization component and a second optical signal transmitted in a second polarization component are multiplexed in the polarization multiplexed optical signal. The signal processing device includes a generator and a compensation circuit. The generator selects the first polarization component or the second polarization component based on modulation formats of the first and second optical signals, and generates a compensation value for compensating for an electric field information signal of a selected polarization component based on the electric field information signal of the selected polarization component. The compensation circuit compensates for electric field information signals of the first and second polarization components using the compensation value generated by the generator.

Abstract: An optical transmitter includes: a mapper that generates an electric field information signal from transmission data; a phase rotation circuit that adds a phase rotation to the electric field information signal; a driver that generates a driving signal from the electric field information signal to which the phase rotation is added; a modulator that generates a modulated optical signal according to the driving signal; and a controller that controls a bias of the modulator according to a change in a carrier frequency of the modulated optical signal corresponding to the phase rotation that is added to the electric field information signal by the phase rotation circuit.

Abstract: A signal processing device includes digital signal processing circuits. Each of the digital signal processing circuits includes: a regeneration circuit that regenerates a bit stream front an electric field information signal of an optical signal; an error correction circuit that corrects an error in the bit stream; an encoder circuit that generates an encoded bit stream from received data; and a generation circuit that generates an electric field information signal from the encoded bit stream. An electric field information signal or a bit stream is given from a regeneration circuit, an encoder circuit or a generation circuit in a first digital signal processing circuit to a second digital signal processing circuit. A regeneration circuit, an error correction circuit or a generation circuit in the second digital signal processing circuit processes the electric field information signal or the bit stream given from the first digital signal processing circuit.

Abstract: There is provided an optical transmission device including: a generator configured to convert an electric signal into a plurality of parallel signals, modulate the plurality of parallel signals, shift center frequencies of spectra of the plurality of modulated parallel signals into different frequencies, so as to generate signals accommodated in a plurality of sub-channels each having different center frequencies, and generate a multiplexed signal by multiplexing the signals accommodated in the plurality of sub-channels; a transmitter configured to optical-modulate the multiplexed signal and transmit the optical-modulated signal to an optical reception device; and a controller configured to control a frequency spacing between adjacent sub-channels of the plurality of sub-channels, based on a monitoring result of reception characteristics of the signals accommodated in the plurality of sub-channels within the multiplexed signal in the optical reception device.

Abstract: An error correction circuit includes a first error correction circuit, a second error correction circuit and a controller. The first error correction circuit performs an error correction in a first correction scheme. The second error correction circuit performs an error correction in a second correction scheme. A correction performance of the second correction scheme is lower than a correction performance of the first correction scheme. The controller makes the first error correction circuit perform error correction of a received signal when a capacity of the received signal is smaller than or equal to a processing capacity of the first error correction circuit, and makes the first error correction circuit and the second error correction circuit perform error correction of the received signal when the capacity of the received signal is larger than the processing capacity of the first error correction circuit.

Abstract: There is provided a transmission apparatus configured to receive a frequency-division multiplexed optical signal generated by modulating carrier light based on a plurality of frequency-division multiplexed subcarrier signals, the transmission apparatus including: a processor configured to: extract a plurality of subcarrier signals of the plurality of frequency-division multiplexed subcarrier signals from the frequency-division multiplexed optical signal; calculate signal qualities of the plurality of subcarrier signals; detect a deviation of the signal qualities between the plurality of subcarrier signals; and perform a frequency control of the carrier light generated by an optical source of a transmission apparatus configured to transmit the frequency-division multiplexed optical signal, based on the deviation of the signal qualities.

Abstract: A signal shifted from a carrier frequency in a frequency domain by using digital signal processing is generated, and the optical modulator is driven with a drive signal based on the signal. A monitor monitors whether or not a component of a modulated signal light output from the optical modulator appears in a specific frequency depending on a frequency shift performed by the digital signal processing, and the controller controls a relation between a sign of the drive signal and an operating point of the optical modulator according to a monitored result.

Abstract: A non-linear distortion compensator includes: a first signal generator configured to generate a signal with a second multivalued level lower than a first multivalued level from an input signal; a non-linear distortion calculator configured to calculate non-linear distortion of the signal with the first multivalued level based on the signal with the second multivalued level generated by the first signal generator; and a non-linear compensator configured to compensate the non-linear distortion of the signal with the first multivalued level based on the non-linear distortion calculated by the non-linear distortion calculator.

Abstract: An optical receiver includes a dividing unit, a control unit, and a compensating unit. The dividing unit divides an optical transmission signal into a plurality of frequency components by a set number of divisions and a set division bandwidth. The control unit controls the number of divisions and the division bandwidth on the basis of transmission path information about an optical transmission line through which the optical transmission signal is transmitted and signal information about the optical transmission signal. The compensating unit compensates optical nonlinear distortion of each of the frequency components divided by the dividing unit.

Abstract: An optical transmitter includes: a mapper configured to generate an electric-field-information signal from transmission data; a training-signal-generation section configured to generate a training signal; a training-signal-insertion section configured to insert the training signal into the electric-field-information signal; a driver configured to generate a drive signal from the electric-field-information signal into which the training signal is inserted; a modulator configured to generate an optical-modulation signal based on the drive signal; an optical receiver configured to generate an intensity signal indicating intensity of the optical-modulation signal; a training-signal-extraction section configured to extract an intensity-training signal corresponding to the training signal, from the intensity signal; a coder configured to generate a coded-training signal by coding the intensity-training signal extracted by the training-signal-extraction section using the training signal generated by the training-sig

Abstract: There is provided a transmission apparatus configured to transmit an optical signal by using a plurality of subcarriers, the transmission apparatus includes: a plurality of modulators, a modulator of the plurality of modulators configured to be capable of changing a modulation format corresponding to a subcarrier of the plurality of subcarriers; a controller configured to control the modulation format for the modulator so as to use a first modulation format and a second modulation format for two or more subcarriers among the plurality of subcarriers and include subcarriers that are different in at least one of a first timing and a second timing of the first modulation format; and a multiplexer configured to multiplex signals modulated by the plurality of modulators.

Abstract: An estimating device includes a detector and an estimator. The detector detects a first parameter representing a ratio of a power of a signal component in received light to a power of a noise component in the received signal, a second parameter representing a sum of the power of the signal component and the power of the noise component, and a third parameter representing a sum of a power of a component being derived from cross phase modulation and being contained in the noise component and a power of a component being derived from spontaneously emitted light and being contained in the noise component. The estimator estimates, based on the first through the third parameters, a fourth parameter representing a ratio of the power of the signal component to a power of a component being derived from self phase modulation and being contained in the noise component.

Abstract: Provided is a frequency error estimating apparatus used for a coherent optical receiver, which determines an amplitude of a baseband digital electrical signal converted from a received light signal modulated with a phase and amplitude shift keying, determines, with respect to each determined amplitude, a modulated phase component of the baseband digital electrical signal based on phase noise estimation values and frequency error estimation values of N previous symbols (N is a positive integer), and calculates a frequency error based on an inter-symbol phase difference of a signal obtained by cancelling the modulated phase component from the baseband digital electrical signal.

Abstract: There is provided an optical transmission device including: a generator configured to convert an electric signal into a plurality of parallel signals, modulate the plurality of parallel signals, shift center frequencies of spectra of the plurality of modulated parallel signals into different frequencies, so as to generate signals accommodated in a plurality of sub-channels each having different center frequencies, and generate a multiplexed signal by multiplexing the signals accommodated in the plurality of sub-channels; a transmitter configured to optical-modulate the multiplexed signal and transmit the optical-modulated signal to an optical reception device; and a controller configured to control a frequency spacing between adjacent sub-channels of the plurality of sub-channels, based on a monitoring result of reception characteristics of the signals accommodated in the plurality of sub-channels within the multiplexed signal in the optical reception device.

Abstract: A network controller includes: a first acquisition unit configured to acquire, based on a signal quality amount of each of wavelength paths set in a network of an optical wavelength-multiplexed transmission system, a signal quality amount of each of spans in each of the wavelength paths; an arithmetic unit configured to calculate a signal quality amount of each of spans in a wavelength path of an estimation target, based on the signal quality amount acquired by the first acquisition unit; and an estimation unit configured to estimate a signal quality amount of the wavelength path of the estimation target, based on the signal quality amount calculated by the arithmetic unit.

Abstract: A receiving device that converts, to a digital signal, a signal in which signal light from an optical transmission path and local oscillation light are mixed, so as to perform digital signal processing, the optical communication receiving device comprising: a frequency offset compensation unit configured to calculate a frequency offset of the digital signal and to, based on the frequency offset, compensate for a phase of the digital signal; a carrier phase recovery unit configured to calculate a carrier phase of the digital signal whose phase is compensated for in the frequency offset compensation unit; and a residual frequency offset detection unit configured to calculate an average of differences in the carrier phase, and to output the average as a residual frequency offset, wherein the frequency offset compensation unit is configured to correct the frequency offset using the residual frequency offset output by the residual frequency offset detection unit.

Abstract: An optical transmission system includes an optical transmitter and an optical receiver. The optical transmitter includes: a first digital signal processor configured to generate an electric-field information signal corresponding to a transmission signal; and a transmitter front-end configured to generate an optical signal from the electric-field information signal. The optical receiver includes: a receiver front-end configured to generate an electric signal corresponding to the optical signal; and a second digital signal processor configured to detect polarization dependent effects on the optical signal based on the electric signal. The first digital signal processor corrects the electric-field information signal based on the polarization dependent effects detected by the second digital signal processor in the optical receiver.

Abstract: A digital coherent receiving apparatus includes a first oscillator for outputting a local light signal of a fixed frequency, a hybrid unit mixing the local light signal with a light signal received by a receiver, a second oscillator for outputting a sampling signal of a sampling frequency, a converter for converting the mixed light signal into digital signal synchronizing with the sampling signal, a waveform adjuster for adjusting a waveform distortion of the converted digital signal, a phase adjustor for adjusting a phase of the digital signal adjusted by the waveform adjustor, a demodulator for demodulating the digital signal adjusted by the phase adjuster, and a phase detector for detecting a phase of the digital signal adjusted by the phase adjuster, and a control signal output unit for outputting a frequency control signal on the basis of the detected phase signal to the second oscillator.

Abstract: An estimating device includes a detector and an estimator. The detector detects a first parameter representing a ratio of a power of a signal component in received light to a power of a noise component in the received signal, a second parameter representing a sum of the power of the signal component and the power of the noise component, and a third parameter representing a sum of a power of a component being derived from cross phase modulation and being contained in the noise component and a power of a component being derived from spontaneously emitted light and being contained in the noise component. The estimator estimates, based on the first through the third parameters, a fourth parameter representing a ratio of the power of the signal component to a power of a component being derived from self phase modulation and being contained in the noise component.

Abstract: A method of tap coefficient correction includes: obtaining a synchronization symbol difference between a first polarization and a second polarization orthogonal to the first polarization; obtaining a delay amount of each of the first polarization and the second polarization in an adaptive equalizer; calculating, in a case where a horizontal axis represents a tap number and a vertical axis represents a tap coefficient and a tap number or a nearest tap number with which an area of a drawn figure is halved is set as a gravity center of tap coefficients, a correction reference gravity center of the tap coefficients set in the adaptive equalizer, based on the synchronization symbol difference and the delay amount; and performing a correction of shifting an entire tap coefficients in units of symbol to cause the correction reference gravity center to be closest to a tap center.