Fujitsu Corporation

Fujitsu Telecom Networks Limited

Toshiki Honda

Takeshi Ono

Takehiro Fujita

Kazuhiro Kunimatsu

Takeshi Hoshida

Yasushi Sugaya

Katsumi Fukumitsu

Masakazu Ozaki

A digital coherent receiver that receives a first optical signal in a WDM optical signal includes: a front-end circuit configured to generate a digital signal indicating the first optical signal; a waveform distortion corrector configured to generate a correction result signal indicating a first optical signal whose waveform distortion has been corrected by performing a digital arithmetic operation on the digital signal using at least one dispersion compensators and at least one nonlinear compensators; and a controller configured to adjust operation states of specified dispersion compensators among the plurality of dispersion compensators and specified nonlinear compensators among the plurality of nonlinear compensators. The number of the specified dispersion compensators and the number of the specified nonlinear compensators are determined based on the number of spans of an optical transmission line through which the first optical signal is transmitted.

Digital coherent receiver and receiving method of optical signal

A transmitter to be added or reduced turns ON/OFF an optical output. A relay station and a receiving terminal station acquire the amount of fluctuation of the optical output of the received signal light when the optical output of the added transmitter is turned ON and OFF. From the amount of fluctuation of the optical output, the number of wavelengths after the addition or reduction is acquired. Without an OSC signal, each station may be informed of the number of wavelengths. Therefore, the configuration for transmitting and receiving the OSC signal is not requested, thereby reducing the total cost, appropriately controlling the gain of the optical amplifier, and successfully maintaining transmission quality.

Wavelength division multiplexing transmission device

An optical receiving device includes: an optical amplifier configured to amplify a wavelength multiplexed optical signal; a demultiplexer configured to demultiplex the amplified wavelength multiplexed signal into optical signals of a plurality of wavelengths; optical receivers configured to regenerate the demultiplexed optical signals; error correction units configured to correct a bit error in the regenerated optical signals; and main control unit. The control unit adjusts RXDTV of the optical receiver for receiving optical signals of a given wavelength to the optimal value in the state where the gain of the optical amplifier is lowered from that of a normal operation such that the occurrence of bit errors in the optical signals of the other wavelengths does not exceed the correction capability of the error correction unit.

Optical receiving device

An optical receiving apparatus includes a variable dispersion compensation unit, a delay interference unit, a photoelectric converter, a polarization control unit for control the polarization state of an optical signal inputted to the photoelectric converter, a received data processing unit for monitoring the number of error occurrences, and a control unit for controlling the dispersion compensation amount at the variable dispersion compensation unit and the optical phase control amount at the delay interference unit, based on information on the number of error occurrences from the received data processing unit. The control unit adjusts the polarization state of the optical signal inputted to the photoelectric converter to a first polarization state, in which errors are more likely to occur than in normal operation, by controlling the polarization control unit and then starts control of the variable dispersion compensation unit and the delay interference unit, and upon completion of the control, adjusts the polarization state of the optical signal to a second polarization state, in which errors are less likely to occur than in the first polarization state, by controlling the polarization control unit.

Optical receiving apparatus and optical transmission system

An optical receiving apparatus is provided with a receiver, a setting unit, and a storage unit. The receiver receives an optical signal modulated in a DPSK format and performs variable dispersion compensation and delay interference processing on the optical signal to demodulate the optical signal. The setting unit sets suitable setting values of the variable dispersion compensation and the delay interference processing for the receiver based on an error condition of the demodulated signal. The storage unit stores the setting values set by the setting unit.

Optical receiving apparatus

The optical transmitter and receiver of the invention includes: a variable dispersion compensator that performs wavelength dispersion compensation on an optical signal of a differential M-phase modulation format input from a transmission path; an optical amplifier that compensates an optical loss in the variable dispersion compensator; a delay interferometer that delays and interference processes the optical signal output from the optical amplifier; and a photoelectric conversion circuit that photoelectric converts the output light from the delay interferometer to generate a demodulated electric signal. The output level of the optical amplifier is decreased at the time of start up to deteriorate the OSNR of the optical signal input to the photoelectric conversion circuit, to thereby realize a state in which an error occurs more easily, and then optimization control of the variable dispersion compensator and the delay interferometer is started. As a result optimization of the dispersion compensation amount and the phase control amount in the optical receiver corresponding to the differential M-phase modulation format can be performed in a short time.

Optical receiver and controlling method thereof, and optical transmission system

An optical signal, which is a low-speed signal superimposed on a high-speed phase modulated optical signal by intensity modulation, is used. In an optical receiver apparatus, a received signal is split, and one of the split signals is O/E converted and low frequency component alone is extracted via a filter. A clock is extracted from low-frequency component by CDR, and is compared with a preset frequency. Using the frequency difference obtained, dispersion compensation is performed with low accuracy. Next, the amount of phase control of the delay interferometeris adjusted so that the amplitude of the electrical signal is maximized. An error rate is measured, and fine adjustment is performed to improve the error rate.

High-speed dispersion compensation control apparatus

A transponder in a wavelength division multiplexing apparatus detects a wavelength of a leak light (received light) having one of plural wavelengths multiplexed or divided by a WDM unit, the leak light having been received from the WDM unit when the transponder is connected to the WDM unit; determines a transmission wavelength which is a wavelength of a light to be transmitted to the WDM unit on the basis of the wavelength of the received light; and sets to convert the wavelength of the light to be transmitted to the WDM unit into the transmission wavelength, and transmit the converted light.

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Kawasaki, Japan

Toshiki Honda