Abstract: An interferometer for demodulating a differential M-phase shift keying signal includes a PLC type interferometer main body, a heating portion that heats the PLC type interferometer main body, and an intermediate member having a higher stiffness than that of the PLC type interferometer main body, for bonding the PLC type interferometer main body and the heating portion with each other while being sandwiched therebetween. A linear expansion coefficient difference between the PLC type interferometer main body and the intermediate member is equal to or smaller than 4.5×10?6/° C., and a thermal conductivity difference between the PLC type interferometer main body and the intermediate member is equal to or larger than 10 W/mK. A phase of an optical signal flowing through the interferometer is adjusted by using the heating portion and a second heating portion.

Abstract: A signal regeneration device which makes an extracted clock signal highly accurate while maintaining superior receiving sensitivity. To this end, a device of the present invention is configured to have a branch section for branching an input electrical signal which has been demodulated from a differential phase-shift modulated state; a first filter for equalizing a waveform of one of the demodulated electrical signals branched by the branch section; a clock recovery section for recovering a clock signal from the demodulated electrical signal whose waveform has been equalized by the first filter; and a data regeneration section for regenerating a data signal from a remaining one of the demodulated electrical signals branched by the branch section and from a clock signal recovered by the clock recovery section.

Abstract: An amount of change of a control signal applied to a polarization controller in a polarization mode dispersion compensator is determined for each feedback loop by evaluating degree of polarization response in past feedback loops.

Abstract: A transmitted optical signal is first subjected to polarization mode dispersion compensation by a polarization mode dispersion compensator (PMDC), and then, its chromatic dispersion is compensated by a variable chromatic dispersion compensator (VDC) after the polarization mode dispersion compensation. How much the optical transmission signal suffers from polarization mode dispersion, which is needed to perform the polarization mode dispersion is measured using a Stokes parameter that is not affected by chromatic dispersion.

Abstract: The invention relates to an optical receiving station, an optical communication system, and a dispersion controlling method for precisely controlling chromatic dispersion in an optical transmission line or chromatic dispersion in an optical transmission line that varies with time. An optical receiving station is provided with a dispersion compensating section for receiving, via an optical transmission line, an optical signal modulated according to an optical duo-binary modulation method and for changing a dispersion value to be used for compensating for chromatic dispersion in an optical transmission line, an intensity detecting section for detecting the intensity of a specific frequency component of the optical signal output from the dispersion compensating section, and a controlling section for adjusting the dispersion value of the dispersion compensating section so that the output of the intensity detecting section has a predetermined extreme value.

Abstract: A dispersion compensation controlling apparatus used in a very high-speed optical communication system adopting optical time division multiplexing system comprises a first specific frequency component detecting unit (2a) detecting a first specific frequency-component in a baseband spectrum in a transmission optical signal inputted to a receiving side over a transmission fiber as a transmission line (6a), a first intensity detecting unit (3a) detecting information on an intensity of the first specific frequency component detected by the first specific frequency component detecting unit (2a and a polarization-mode dispersion controlling unit (220a) con trolling a polarization-mode dispersion quantity of the transmission line (6a) such that the intensity of the first specific frequency component detected by the first intensity detecting unit. (3a) becomes the maximum, thereby easily detecting and compensating polarization-mode dispersion generated in a high-speed optical signal.

Abstract: The degree of polarization of an optical signal is measured by a polarimeter and used for providing a feedback signal to adjust adaptive optics of a polarization mode dispersion compensator. The polarization properties of the polarimeter are determined with high accuracy to match the polarimeter through calibration and used to produce the feedback signal.

Abstract: The invention relates to an optical receiving station, an optical communication system, and a dispersion controlling method for precisely controlling chromatic dispersion in an optical transmission line or chromatic dispersion in an optical transmission line that varies with time. An optical receiving station is provided with a dispersion compensating section for receiving, via an optical transmission line, an optical signal modulated according to an optical duo-binary modulation method and for changing a dispersion value to be used for compensating for chromatic dispersion in an optical transmission line, an intensity detecting section for detecting the intensity of a specific frequency component of the optical signal output from the dispersion compensating section, and a controlling section for adjusting the dispersion value of the dispersion compensating section so that the output of the intensity detecting section has a predetermined extreme value.

Abstract: A dispersion compensation method comprising the steps of: a) providing a compensation node for each predetermined number of in-line repeaters; b) carrying out dispersion compensation for the in-line repeaters with the different bit rates in common; c) carrying out wavelength demultiplexing on the optical signal for each of the different bit rates in the compensation node; and d) setting an optimum dispersion compensation amount for the optical signal of each bit rate.

Abstract: In the WDM optical transmission system, a high-slope dispersion compensator compensates wavelength dispersion produced in the optical transmission line. The high-slope dispersion compensator has a dispersion slope characteristic, by which a dispersion slope is substantially compensated over the wavelength bandwidth of the optical transmission line, and also a dispersion compensation characteristic, by which the residual dispersion produced after compensating the dispersion slope using the above dispersion slope characteristic becomes symmetrical with respect to a wavelength in the vicinity of the center of the wavelength bandwidth. To achieve the above compensation, a wavelength-multiplexed signal is divided into wavelength bandwidth groups, and the residual dispersion of the optical transmission line is compensated on a group-by-group basis for the wavelength bandwidth groups.

Abstract: By comprising a unit 2 making the adjustment related to degradation compensation of a plurality of signals with each wavelength made after multiplexing the signals, a unit 3 multiplexing the outputs of a plurality of units 2, a unit 4 compensating for the waveform degradation of the output of the unit 3, a unit 5 selecting a component with one of a plurality of wavelengths from a part of the output of the unit 4 and a unit 6 detecting the degree of signal degradation from the output of the unit 5 and controlling the adjustment by the unit 2 corresponding to the selected frequency so as to reduce the degree, components disposed for each wavelength in an optical transmission system adopting a wavelength-division multiplexing method can be shared, and the size and cost of an compensator can be reduced.

Abstract: An apparatus which compensates for dispersion in an optical transmission line. The apparatus includes a fixed dispersion compensator and a variable dispersion compensator. The fixed dispersion compensator has a fixed dispersion amount and coarsely compensates for the dispersion in the transmission line. The variable dispersion compensator has a variable dispersion amount and finely compensates for the dispersion in the transmission line. The fixed and variable dispersion compensators can be located at many positions. For example, one may be in a transmitter and the other may be in a receiver. Both may be in the transmitter and/or the receiver. One may be in either the transmitter or the receiver, with the other in an optical repeater positioned along the transmission line.

Abstract: The invention provides an optical wavelength multiplex transmission method wherein a band in the proximity of a zero dispersion wavelength of an optical fiber is used and optical signals are disposed at efficient channel spacings taking an influence of the band, the wavelength dispersion and the four wave mixing into consideration to realize an optical communication system of an increased capacity which is not influenced by crosstalk by FWM. When optical signals of a plurality of channels having different wavelengths are to be multiplexed and transmitted using an optical fiber, a four wave mixing suppressing guard band of a predetermined bandwidth including the zero-dispersion wavelength ?0 of the optical fiber is set, and signal light waves of the plurality of channels to be multiplexed are arranged on one of the shorter wavelength side and the longer wavelength side outside the guard band.

Abstract: Disclosed herein are a method and system for compensating chromatic dispersion. The method includes the steps of generating WDM signal light by wavelength division multiplexing a plurality of optical signals having different wavelengths, transmitting the WDM signal light by an optical fiber transmission line, and receiving the WDM signal light transmitted by the optical fiber transmission line. The receiving step includes the steps of detecting chromatic dispersion related to at least one of the plural optical signals, and providing a variable dispersion compensator whose chromatic dispersion and dispersion slope are controlled so that the detected chromatic dispersion is reduced. According to this method, waveform degradation due to dispersion can be compensated with high accuracy in consideration of dispersion and dispersion slope.

Abstract: An apparatus which compensates for dispersion in an optical transmission line. The apparatus includes a fixed dispersion compensator and a variable dispersion compensator. The fixed dispersion compensator has a fixed dispersion amount and coarsely compensates for the dispersion in the transmission line. The variable dispersion compensator has a variable dispersion amount and finely compensates for the dispersion in the transmission line. The fixed and variable dispersion compensators can be located at many positions. For example, one may be in a transmitter and the other may be in a receiver. Both may be in the transmitter and/or the receiver. One may be in either the transmitter or the receiver, with the other in an optical repeater positioned along the transmission line.

Abstract: A transmitted optical signal is first subjected to polarization mode dispersion compensation by a polarization mode dispersion compensator (PMDC), and then, its chromatic dispersion is compensated by a variable chromatic dispersion compensator (VDC) after the polarization mode dispersion compensation. How much the optical transmission signal suffers from polarization mode dispersion, which is needed to perform the polarization mode dispersion is measured using a Stokes parameter that is not affected by chromatic dispersion.

Abstract: A polarization converter followed by two PMFs adjusts principal states of polarization (PSP) of a PMD compensator against PSP of an optical transmission line, and a mode-coupling adjuster between the PMFs adjusts a differential group delay and a PSP rotation rate of the PMFs.

Abstract: The present invention provides a wavelength division multiplexing transmission system for separating wavelength division multiplexing signals, where signal lights with different bit rates are wavelength division multiplexed, according to the bit rate, and processing the separated signals individually. The wavelength division multiplexed signals, where a low-speed bit rate signal is disposed in an odd channel group and a high-speed bit rate signal is disposed in an even channel group, are demultiplexed into a low-speed signal group and a high-speed signal group by an unequal bandwidth interleaver. The low-speed signal group is processed (e.g. demultiplexing, dispersion compensation) by an optical device appropriate for the low-speed signals, and the high-speed signal group is processed by an optical device appropriate for the high-speed signals.

Abstract: An object of the invention is to provide a method and apparatus of PMD compensation, which enable of compensating for polarization-mode dispersion (PMD) occurring in signal light, at high accuracy over a wide range.

Abstract: The dispersion monitoring device of the present invention detects a change in dispersion caused in a system by performing the decision process of a received signal using a data flip-flop in which required decision phase and decision threshold are set, averaging the output signal of the data flip-flop using an integration circuit and determining a received waveform, based on a change in a level of an output signal from the integration circuit. In another preferred embodiment, a signal is inputted to a chromatic dispersion change sign monitor. If a chirping parameter is correctly set, residual chromatic dispersion shifts in the negative direction when the peak value of a received signal is large, and it shifts in the positive direction when the peak value of a received signal is small. Using this fact, optimum dispersion compensation is conducted.