Abstract: A polarization multiplexing and transmitting apparatus generates polarization multiplexed light by multiplexing modulated signal components that having varying intensities and are in polarization states orthogonal to each other. The polarization multiplexing and transmitting apparatus includes a converting unit that converts light generated by a light source into signal components having a varying intensity synchronized with a clock signal input thereto and a varying intensity inversely synchronized with the clock signal, respectively; a modulating unit that modulates the signal components, respectively; and a polarization adjusting unit that orthogonalizes polarization states of the signal components.

Abstract: An optical mixing part mixing a received optical signal and local oscillator light in at least two kinds of phases and extracting at least two-system optical signals corresponding to each light phase; a photoelectric conversion part converting the at least two-system optical signals obtained in the optical mixing part into electric analog signals; an analog-to-digital conversion part converting the electric analog signals into digital signals; and a control part processing the digital signals thereby detecting a light phase difference between the respective systems in the optical mixing part and supplying a signal for correcting the light phase between the systems to the optical mixing part to control the optical mixing part so that the light phase difference becomes to zero or close to a desired value when the light phase difference has a shift from the desired value.

Abstract: The present invention discloses filter coefficient changing apparatus and method for use in a dual-polarized optical coherent receiver. The apparatus comprises a controlling unit, a switching unit and a new coefficient obtaining unit. The switching unit is connected between a first filter coefficient updating unit and a first filtering unit and a second filtering unit; the new coefficient obtaining unit generates new filter coefficients for the first filtering unit and the second filtering unit in accordance with filter coefficients outputted by a second filter coefficient updating unit; and the controlling unit generates a control signal that controls switching of the switching unit.

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: The present invention relates to filter, coherent receiver device and coherent receiving method. The filter is used for converting a partial response signal into a full response signal, wherein the filter uses the following transfer function HPre-Filter(z) with respect to a partial response signal having a transfer function H PR ? ( z ) = A ? ( 1 + z - 1 ) m ? ( 1 - z - 1 ) n : ? ? H Pre - Filter ? ( z ) = 1 A ? ( 1 + ? ? ? z - 1 ) m ? ( 1 - ? ? ? z - 1 ) n , in which A is other item, m and n are integers larger than or equal to 0 but not being 0 at the same time, 0<?<1.

Abstract: An optical receiver includes an optical front-end, a digital converter, a frequency-characteristic-difference reducing unit and an identifying unit. The optical front-end splits an input signal light into signal light components on a basis of local light and converts the split signal light components into electrical signals. The digital converter converts the electrical signals, converted by the optical front end, into digital signals. The frequency-characteristic-difference reducing unit reduces a frequency-characteristic difference between the digital signals converted by the digital converter. The identifying unit identifies each of the digital signals whose frequency-characteristic difference is reduced by the frequency-characteristic-difference reducing unit.

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: An apparatus includes a first estimator that estimates a signal quality based on an error correction number of an electrical signal obtained by photoelectrically converting a received optical signal; a second estimator that estimates a signal quality from which the influence of nonlinear effects is removed based on signals upstream and downstream of an identification calculator identifying the electrical signal; and a calculator that calculates the difference between the signal qualities estimated by the first and second estimators to calculate the amount of nonlinear effects.

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: In-phase signal light and quadrature-phase signal light obtained by mixing input light and local light with each other are converted into digital signals. The quality of a signal to be received is monitored with reference to information obtained through digital signal processing, and the power ratio between the input signal light and the local light that are to be mixed with each other are controlled on the basis of the result of the monitoring.

Abstract: A signal processing device includes: a phase controller configured to control respective phases of an in-phase signal and an quadrature signal, which are obtained by converting an analog signal into a digital signal when a multi-value phase modulation light is demodulated, by digital signal processing; and a control amount provider configured to provide a control amount to the phase controller based on an output of the phase controller.

Abstract: A distortion compensating apparatus which compensates for distortion in a waveform of a received light signal through a digital signal processing includes a plurality of fixed amount compensators which compensate for the distortion in the waveform at respective given compensating amounts. The combination of operating states of the plurality of fixed amount compensators is changed by on/off switching of each of the plurality of fixed amount compensators, and the plurality of fixed amount compensators are cascaded.

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: While altering a plurality of wavelength setting parameters according to a control sequence, a local oscillation light having a wavelength controlled by those wavelength setting parameters is generated. Further, the received signal light and the generated local oscillation light are mixed, and if an electric signal is generated by photoelectric conversion from the resulting light, then the wavelength control of the local oscillation light is terminated.

Abstract: An optical receiver includes a photo-detector that converts a received optical signal into an electric signal and outputs the electric signal, a converter that converts the electric signal into a parallel data signal and outputs the parallel data signal, and parallel-number changer changing a parallel number of the parallel data signal in accordance with a bit rate of the optical signal and outputting the parallel data signal having the changed parallel number.

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: 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: In present invention, a filter coefficient adjustment apparatus is used in a polarization demultiplexer which demultiplexes the input signals by using filters to obtain demultiplexed output signals, said filter coefficient adjustment apparatus being used for adjusting the coefficients of the filters, wherein said filter coefficient adjustment apparatus comprises: an logarithm partial derivative calculation unit for calculating the logarithm partial derivative value of a target probability density function of the demultiplexed output signals when its self-variable value is the present demultiplexed output signal value; a gradient calculation unit for calculating the gradient of a target optimizing function for optimizing the distribution of the multiplexed output signals based on the logarithm partial derivative value calculated by the logarithm partial derivative calculation unit; and a filter coefficient updating unit for updating the coefficients of the filters based on the gradient calculated by the gradie

Abstract: An optical receiving apparatus includes a combining unit that combines signal light and reference light; a optoelectric converting unit that converts, into electrical signals, two or more optical signals that enable reconstruction of a complex electric field signal of the signal light obtained by the combining unit; and a sampling clock generating unit that generates a sampling clock that has a frequency preset based on a symbol rate of the signal light and is asynchronous with the signal light. The optical receiving apparatus further includes a digital converting unit that samples at the frequency of the sampling clock signal, an electrical signal obtained by the optoelectric converting unit and converts the electrical signal into a digital signal; and a digital signal processing unit that demodulates a received signal based on a complex digital signal obtained from the digital signal obtained by the digital converting unit.

Abstract: The present invention relates to an adaptive equalizer and an adaptive equalizing method. The adaptive equalizer comprises an adaptive equalizing unit, for adaptively equalizing an inputted signal to output the equalized signal; a coefficient updating unit, for updating a coefficient of a filter of the adaptive equalizing unit; a switching unit, connected between the coefficient updating unit and the adaptive equalizing unit, wherein when the switching unit is on, the coefficient updating unit is capable of updating the coefficient of the adaptive equalizing unit, and when the switching unit is off, the coefficient updating unit is incapable of updating the coefficient of the adaptive equalizing unit; and a monitoring device, for controlling on or off of the switching unit in accordance with a down sampling phase of the inputted signal or a down sampling phase of the equalized signal.