Abstract: A receiver includes: an extraction circuit to extract a phase fluctuation component common to phase data of two polarization components that are separated in a coherent reception of a polarization multiplexing phase modulation optical signal; and a correction circuit to correct the phase data of the two polarization components in accordance with the phase fluctuation component.

Abstract: A frequency modulation signal demodulator includes: an optical signal that has a wavelength, a frequency modulation signal being superimposed onto the optical signal; an optical filter that inputs the optical signal and has a central wavelength of a pass band at a wavelength that is shifted from a central wavelength of a spectrum of the optical signal and that is set to allow the pass band to be located at one portion of the spectrum; and an asymmetry optical interferometer that demodulates the frequency modulation signal by splitting light which has passed through the optical filter, delaying different time between split lights, and interfering the split lights.

Abstract: An excitation light source, for Raman amplification, includes a polarization beam splitter (PBS) for splitting a laser beam from an excitation laser into two polarization components, and a polarization beam combiner (PBC) for combining the two polarization components, and a time difference generator provided between PBS and PBC. The time difference generator generates a difference in propagation time between the two polarization components.

Abstract: An optical transmission/reception system includes a modulator for modulating light based on data to output signal light; a transmission-side signal processor performing transmission-side digital signal processing which imparts a polarization change to the signal light by the optical modulation with respect to an input signal; an optical transmitter in which the modulator performs the optical modulation based on the input signal subjected to the transmission-side digital signal processing in the transmission-side signal processor; and an optical receiver including a converter converting the signal light inputted from the optical transmitter via a transmission path to a digital electric signal for each polarization component, and a reception-side signal processor performing reception-side digital signal processing which imparts a polarization change having a property substantially inverse to a property of the polarization change in the transmission-side signal processor with respect to the digital electric sign

Abstract: A light receiving device includes: a converter digitalizing an analog signal with a given sampling clock frequency, the analog signal being obtained through a photoelectric conversion of a received optical signal; a plurality of fixed distortion compensators compensating an output signal of the converter for waveform distortion with a fixed compensation amount that is different from each other; a plurality of phase shift detector circuits detecting a sampling phase shift from an output signal of the plurality of the fixed distortion compensators; a phase-adjusting-amount determiner determining a sampling phase adjusting amount with use of an output signal of the plurality of the phase shift detector circuits; and a phase adjusting circuit reducing a phase difference between the sampling clock frequency and the received optical signal based on a determination result of the phase-adjusting-amount determiner.

Abstract: A method and apparatus for compensating nonlinear damage are disclosed. The method for compensating nonlinear damage, including: determining an additive parameter indicating an amount of nonlinear damage based on a plurality of sampled signal sets among which a sampling time of an input signal varies according to different time; and subtracting the additive parameter from the input signal.

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: The present invention provides apparatus for self-phase modulation noise calculation, apparatus for self-phase modulation noise elimination and optical coherent receiver. The apparatus for calculation comprises: a signal receiver to receive an input signal; a calculator connected to the signal receiver to calculate a self-phase modulation noise at the current instant by using the signal powers of an input signal waveform at the current instant and at several sampling instants adjacent to the current instant. The embodiments of the present invention calculates the self-phase modulation noise at a certain instant by using the signal powers at a plurality of digital sampling periods before and after this instant, and when the apparatus is used to calculate the self-phase modulation noise of each of the sub-spans in an optical fiber transmission link, in case that the calculation precision is ensured, the granularity of the sub-spans may be reduced, thereby lowering the complexity of the calculation.

Abstract: An optical receiver includes a splitter that splits a local oscillator lightwave into a first local oscillator lightwave and a second local oscillator lightwave; a measurement unit that measures phase variation of the first local oscillator lightwave; a receiving unit that receives a signal lightwave and the second local oscillator lightwave and mixes these lightwaves and converts the mixed lightwaves into digital signal; a dispersion compensator that reduces chromatic dispersion of the digital signal; a phase processing unit that rotates phase of the dispersion-reduced signal based on the phase variation; and a discriminating unit that discriminates the phase-rotated signal.

Abstract: An optical transmitter includes: a digital signal processor to generate a drive signal from input data; a controller to control an amplitude or power of the drive signal according to information relating to the digital signal processing of the digital signal processor; and an optical modulator to modulate input light with the drive signal controlled by the controller to generate an optical signal.

Abstract: A method and system for reducing crosstalk among subcarriers of a super-channel may apply a frequency shift to selected intermediate subcarrier bands upon optical modulation. The frequency shift may be applied to equally spaced optical frequencies between a first optical frequency and a last optical frequency respectively corresponding to two end subcarrier bands that define a fixed bandwidth of the super-channel. The frequency shift may result in the intermediate subcarrier bands being optically modulated at variably spaced optical frequencies within the fixed bandwidth of the super-channel.

Abstract: A phase shift unit provides a prescribed phase difference (?/2, for example) between a pair of optical signals transmitted via a pair of arms constituting a data modulation unit. A low-frequency signal f0 is superimposed on one of the optical signals. A signal of which phase is shifted by ?/2 from the low-frequency signal f0 is superimposed on the other optical signal. A pair of the optical signals is coupled, and a part of which is converted into an electrical signal by a photodiode. 2f0 component contained in the electrical signal is extracted. Bias voltage provided to the phase shift unit is controlled by feedback control so that the 2f0 component becomes the minimum.

Abstract: A wavelength-tunable light source includes light sources having differing variable wavelength regions, where light sources having adjacent wavelength regions are distributed to different systems. The light sources are each set such that an end portion of the variable wavelength region of the light source overlaps an end portion of the variable wavelength region of another light source. A control unit selects and drives a first light source of a first system, varies a wavelength of the first light source, selects a second light source that is of a second system among the different systems and that has a wavelength region overlapping the variable wavelength region of the first light source, drives the second light source concurrently with the first light source and subsequently switches to the output light of the second light source, causing wavelength variation and executing continuous wavelength variation over a wide range.

Abstract: A light receiving device includes: a converter digitalizing an analog signal with a given sampling clock frequency, the analog signal being obtained through a photoelectric conversion of a received optical signal; a plurality of fixed distortion compensators compensating an output signal of the converter for waveform distortion with a fixed compensation amount that is different from each other; a plurality of phase shift detector circuits detecting a sampling phase shift from an output signal of the plurality of the fixed distortion compensators; a phase-adjusting-amount determiner determining a sampling phase adjusting amount with use of an output signal of the plurality of the phase shift detector circuits; and a phase adjusting circuit reducing a phase difference between the sampling clock frequency and the received optical signal based on a determination result of the phase-adjusting-amount determiner.

Abstract: Light output from a seed light source generation unit that outputs continuous light having a single frequency or a plurality of frequencies is input by a multi-wavelength light source to an optical circulation unit, and light having a plurality of frequencies that is frequency-synchronized with seed light output from the seed light source generation unit is generated. The optical circulation unit is provided with an optical frequency shifter to shift light frequencies, and includes a circulation circuit to return output from the optical frequency shifter to the input side. On a circulation path, an optical spectral shaper capable of adjusting an optical amount of attenuation for each frequency unit is provided so that optical amount of attenuations are adjusted, and thereby the number and the like of optical frequencies output from the optical circulation unit are changed.

Abstract: A control timing synchronization method is executed by a first and a second optical transmission apparatus. The first optical transmission apparatus: superimposes on a main signal and transmits, information of control process details; waits for a first period; subsequently, superimposes on the main signal and transmits, a message giving notification of control start timing; waits for a second period; and subsequently switches a process of the first optical transmission apparatus to a process corresponding to the control process details. The second optical transmission apparatus: acquires the information on the main signal; waits until detection of the message on the main signal, when a process is present that is to be executed by the second optical transmission apparatus based on the information; waits for the second period when the message is detected while waiting for the detection of the message; and subsequently, executes a process corresponding to the information.

Abstract: At least one of a first device, a second device, and a relay device compensates for wavelength dispersion in a first optical wavelength path. The first or second device changes a wavelength dispersion compensation amount at the first or second device so that wavelength dispersion in a second optical wavelength path is compensated. The relay device changes a wavelength dispersion compensation amount at the relay device so that a total amount of wavelength dispersion of the signal light compensated in the first optical wavelength path does not change substantially with the change in the wavelength dispersion compensation amount at the first or second device. The first optical wavelength path is switched to the second optical wavelength path after the wavelength dispersion compensation amount at the first or second device is changed to a value that can compensate for the wavelength dispersion in the second optical wavelength path.

Abstract: A clock signal from a single reference clock is frequency converted, and the frequency-converted signal is input to an equal-interval-optical-frequency-comb generator and a modulator of an optical modulator. By varying the electric frequency of the clock signal input to the equal-interval-optical-frequency-comb generator, frequency intervals of a frequency comb to be generated can be varied, while by selectively employing a particular optical frequency from among the continuous light beams of the generated frequency comb, a frequency comb having unequal intervals can be generated. It is also possible to vary the modulation rate by varying the clock frequency of a driving signal to be input to the optical modulator. By using a clock signal of a single reference clock, the frequency intervals of the frequency comb and the variation of the modulation rate synchronize with each other.

Abstract: A distortion compensator, an optical receiver and a transmission system including an operation selectively compensating for linear waveform distortion exerted on an optical signal via a plurality of distortion compensators and compensating for nonlinear waveform distortion exerted on the optical signal using nonlinear distortion compensators.

Abstract: A signal detection circuit includes: a first optical filter configured to filter an optical signal carrying a frequency modulated signal with a first transmission band; a second optical filter configured to filter the optical signal with a second transmission band; a first photo detector configured to convert the output light of the first optical filter into a first electrical signal; a second photo detector configured to convert the output light of the second optical filter into a second electrical signal; a difference circuit configured to output a signal representing a difference between the first electrical signal and the second electrical signal; and a detector configured to detect the frequency modulated signal based on the output signal of the difference circuit.