Abstract: A measurement device includes a first obtaining unit configured to obtain a first power ratio that indicates a ratio of optical signal power of a first wavelength in a first spectrum at a reception device to optical signal power of a second wavelength different from the first wavelength in the first spectrum; a second obtaining unit configured to obtain a second power ratio that indicates a ratio of optical signal power of the first wavelength in a second spectrum at a transmission device to optical signal power of the second wavelength in the second spectrum; a calculation unit configured to calculate an OSNR of the optical signal at the reception device using the first power ratio obtained by the first obtaining unit and the second power ratio obtained by the second obtaining unit; and an output unit configured to output the OSNR calculated by the calculation unit.

Abstract: An optical signal demodulator includes: an obtaining unit configured to obtain a spectrum of an optical signal generated by a second signal being superimposed on a first signal using frequency modulation; an identifying unit configured to identify a peak wavelength which is a wavelength corresponding to a peak position of the spectrum; and a demodulating unit configured to demodulate the second signal from the optical signal using a wavelength-variable filter to which a transmitted wavelength band has been set based on the peak wavelength.

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.

Abstract: A monitoring apparatus, that monitors a wavelength tunable optical filter for filtering an optical signal to which a frequency modulation component is added, includes: an optical filter configured to filter the optical signal output from the wavelength tunable optical filter; a detector configured to detect amplitude of the frequency modulation component included in the optical signal output from the optical filter; a generator configured to generate an output-side amplitude distribution representing a distribution of the amplitude of the frequency modulation component detected by the detector, by sweeping a transmission wavelength of the optical filter; and a monitoring unit configured to monitor arrangement of a transmission wavelength band of the wavelength tunable optical filter with respect to a spectrum of the optical signal based on the output-side amplitude distribution generated by the generator.

Abstract: In a digital signal processing circuit of an optical receiver applicable to this method for electric power supply control, tap coefficients of a filter used in a waveform equalization section are calculated in a tap coefficient calculating section, based on a state of an optical fiber transmission line. Then, among the calculated tap coefficients, a tap coefficient for which an absolute value is less than a previously determined threshold is determined, and electric power supply to a circuit part of a filter corresponding to the tap coefficient is stopped. As a result, for an optical receiver that performs digital signal processing, it is possible to reduce the power consumption, while realizing waveform equalization at a high accuracy.

Abstract: An optical transmission device includes a transmission unit, a filter unit, a detection unit, and a control unit. The transmission unit superimposes identical superimposition signals of a frequency modulation method on a plurality of optical signals that have identical destinations and that have adjacent wavelengths, and transmits resultant signals as one communication signal. The filter unit filters part of two optical signals having adjacent wavelengths from among the plurality of optical signals included in the communication signal. The detection unit generates an electric signal of a detection level representing an optical intensity of the two optical signals that were filtered by the filter unit. The control unit controls timings of superimposing the superimposition signals on the two optical signals respectively by controlling the transmission unit so that variation in the detection level becomes smaller.

Abstract: A polarization fluctuation compensation device, when WDM light received by, for example, an optical reception device includes a polarization scrambled optical signal and a non-polarization scrambled optical signal, collects information related to whether optical signals having respective wavelengths are polarization scrambled, obtains a target value of control parameters which are different from each other, according to the speed of polarization fluctuations in the non-polarization scrambled optical signal based on the collected information, and performs reception processing of the non-polarization scrambled optical signal by using a control parameter set as the target value. As a result, an influence of fast polarization fluctuations generated resulting from an interaction between optical signals having respective wavelengths can be reliably compensated for, thereby enabling to realize excellent reception characteristics.

Abstract: An optical transmission system includes: an optical transmission device that has a plurality of optical transmitters configured to output at least one different wavelength and a multiplexer configured to multiplex wavelength lights output by the plurality of optical transmitters and output a multiplexed wavelength light; and a detection unit configured to detect each wavelength light that is branched before being fed into the multiplexer by sweeping an objective wavelength for detection, wherein, in a single sweeping, the detection unit selects and detects two or more wavelength lights with a wavelength interval that is wider than a wavelength interval of an output light of the multiplexer.

Abstract: This invention relates to crosstalk coefficient estimating apparatus and crosstalk coefficient estimating method. The crosstalk coefficient estimating apparatus is used to estimate a crosstalk coefficient of crosstalk inflicted on one channel of an optical fiber transmission system comprising two or more channels. The crosstalk coefficient estimating apparatus comprises a complex conjugate unit, for obtaining a complex conjugate signal for signal in one polarization-state of another channel other than said one channel; a multiplying unit, for multiplying the complex conjugate signal obtained by the complex conjugate unit with signal in another polarization-state of the another channel; and a filter, for filtering the multiplication result of the multiplying unit to obtain a crosstalk coefficient of crosstalk inflicted on the signal in one polarization-state of said one channel, wherein a transmission function of the filter is set according to system parameters of the optical fiber transmission system.

Abstract: The present application discloses a method for adaptive blind equalization of a PSK signal, an equalizer and a receiver. According to embodiments as provided, a conjugate product of a current output and a precedent output of an FIR filter is calculated, an equalization coefficient is updated using the conjugate product, and then an input signal is filtered using the FIR filter with the updated equalization coefficient. The embodiments as provided is applicable to adaptive blind equalization of any phase shift keying signal including a BPSK signal.

Abstract: An optical transmission system, where in an optical transmitter a detection bit having a specific pattern set according to the number of bits to be transmitted within one symbol time, is imparted with respect to a transmission signal in which transmission information has been encoded according to a preset format, and an optical signal generated by modulating light according to the transmission signal is transmitted to a transmission line. In an optical receiver, logic inversion or bit swap of received data is detected and compensated by using the detection bit included in the received signal, a decoding process of the compensated received signal is executed. As a result, when an optical signal capable of transmitting multi-bit information within one symbol time is transferred, it is possible to realize excellent transmission characteristics, by reliably compensating an error in received data caused by the modulation format or the multiplex system of the optical signal.

Abstract: A simulation method for a cascade communication system comprising a nodes sequence numbered as 1 to N from a transmitter to a receiver, comprises: acquiring simulation parameters; calculating reverse transfer functions of the nodes; determining a current node in the sequence; adding noise that should be added at the current node to a simulation signal of a previous node; simulating the current node to generate a simulation signal of the current node, by using the simulation signal of the previous node added with the noise that should be added at the current node, based on the reverse transfer function of the current node; judging whether simulations of all the nodes are completed; if yes, repeating the adding and the simulating; if not, determining a cost of the based on the simulation signal of the current node.

Abstract: An optical power monitor that detects optical power of respective wavelengths of a signal light in a wavelength multiplexing system, includes: a light emitter configured to superimpose a frequency modulation component on a signal light; a wavelength tunable filter configured to sweep a pass band of the signal light across a wavelength band for a signal light; and a detector configured to detect intensity changes in optical power passing through the wavelength tunable filter with a frequency modulation of the optical power, and to detect an optical power measurement value at a middle point of two points of the intensity changes of the optical power as the optical power of a wavelength to be measured.

Abstract: A simulation method for a cascade communication system comprising a nodes sequence numbered as 1 to N from a transmitter to a receiver, comprises: acquiring simulation parameters; calculating reverse transfer functions of the nodes; determining a current node in the sequence; adding noise that should be added at the current node to a simulation signal of a previous node; simulating the current node to generate a simulation signal of the current node, by using the simulation signal of the previous node added with the noise that should be added at the current node, based on the reverse transfer function of the current node; judging whether simulations of all the nodes are completed; if yes, repeating the adding and the simulating; if not, determining a cost of the based on the simulation signal of the current node.

Abstract: This invention relates to an apparatus and a method for controlling a filter coefficient. The filter coefficient control apparatus controls a coefficient of a filter of a phase recovering apparatus, and comprises a phase offset obtaining means, for obtaining a phase offset between a carrier and a local oscillation; an autocorrelation calculating means, for calculating an autocorrelation and related statistics of the phase offset; and a filter coefficient determining means, for determining the coefficient of the filter in accordance with the autocorrelation and related statistics.

Abstract: An optical transmitter includes: a pre-compensator calculating an electrical field of an optical signal subjected to an electronic pre-compensation with respect to an input digital signal; a parallelizer parallelizing the electrical field of the optical signal calculated by the pre-compensator; a plurality of optical modulators modulating an optical signal based on each of parallelized electrical fields of optical signals; and a time-division multiplexer time-division-multiplexing an optical signal output from the plurality of the optical modulators.

Abstract: This application relates to an apparatus and a method for equalizing chromatic dispersion and a digital coherent optical receiver. The apparatus for equalizing chromatic dispersion comprising: a chromatic dispersion equalizing unit, for compensating chromatic dispersion of an input signal; and an additional time delay removing unit, for removing, in accordance with frequency offset of the input signal, chromatic dispersion equalization time delay generated by the chromatic dispersion equalizing unit.