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: 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: 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: 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 &lgr;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: 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 &lgr;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: An optical modulator having a voltage—optical output characteristic in which optical output varies periodically with respect to a voltage value of an electrical drive signal is driven by a modulator driving voltage signal, which has an amplitude of 2·V&pgr; between two light-emission culminations or two light extinction culminations of the voltage—optical output characteristic. A low-frequency superimposing unit superimposes a prescribed low-frequency signal on the modulator driving voltage signal, and an operating-point controller controls the operating point of the optical modulator by detecting operating-point drift of the optical modulator based upon the low-frequency signal component contained in an optical signal output from the optical modulator and controlling the bias voltage of the optical modulator in dependence upon the drift of the operating point of the optical modulator.

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 &lgr;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: An apparatus includes a driving voltage generator that generates a pulse driving voltage having a rising edge and a decaying edge. An optical modulator produces a first pulse at the rising edge of the pulse driving voltage and a second pulse at the decaying edge of the pulse driving voltage. Therefore, the first and second pulses are both produced from a single driving pulse voltage. The frequency of the first pulse is determined by the slope of the rising edge of the pulse driving voltage and the frequency of the second pulse is determined by the slope of the decaying edge of the pulse driving voltage. The first and second pulses are transmitted through a transmission line. A detection device detects the first and second pulses after being transmitted through the transmission line.

Abstract: An optical modulator having a voltage—optical output characteristic in which optical output varies periodically with respect to a voltage value of an electrical drive signal is driven by a modulator driving voltage signal, which has an amplitude of 2·V&pgr; between two light-emission culminations or two light extinction culminations of the voltage—optical output characteristic. A low-frequency superimposing unit superimposes a prescribed low-frequency signal on the modulator driving voltage signal, and an operating-point controller controls the operating point of the optical modulator by detecting operating-point drift of the optical modulator based upon the low-frequency signal component contained in an optical signal output from the optical modulator and controlling the bias voltage of the optical modulator in dependence upon the drift of the operating point of the optical modulator.

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 &lgr;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: 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 &lgr;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: 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 &lgr;&thgr; 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: A method for extracting a timing signal produces a data signal from a first portion of an optical signal, extracts a timing signal from a second portion of the optical signal and adds dispersion compensation to at least one of the first and second portions of the optical signal to thereby control the amount of total dispersion in the second portion of the optical signal to be substantially different from the amount of total dispersion in the first portion of the optical signal. The timing signal extracting device uses a signal reproduction circuit to produce the data signal, a signal extraction circuit to extract the timing signal and a chromatic dispersion control apparatus to add dispersion compensation. The optical signal may be modulated by a data signal having a bit rate of X bits/second and the extracted timing signal may have a frequency of X hertz. The signal extraction circuit may be used with a phase locked loop.

Abstract: The invention provides an optical time division demultiplexing apparatus which can perform optical time division demultiplexing while compensating for an operating point drift of an optical time division multiplex signal. The optical time division demultiplexing apparatus includes a clock signal generation element for generating a clock signal for optical time division demultiplexing processing of a received optical signal, and an optical switch for time division demultiplexing the optical signal based on the clock signal from the clock signal generation element.

Abstract: A method and apparatus for optimizing dispersion in an optical fiber transmission line. The method and apparatus (a) determine an optimum amount of total dispersion of an optical transmission line corresponding to a power level of an optical signal transmitted through the optical transmission line; (b) control dispersion of the optical transmission line so that the total dispersion up to a specific point along the optical transmission line becomes approximately zero; and (c) add dispersion to the optical transmission line downstream of the specific point, to obtain the determined optimum amount of total dispersion. The control of dispersion in (b), above, can be performed in several different manners. For example, the control of dispersion can include (i) detecting the intensity of a specific frequency component of the optical signal, the optical signal having an intensity v.

Abstract: The invention provides a technique for optimizing transmission conditions to achieve large-capacity transmission, and also provides peripheral techniques for the practical implementation of optical multiplexing that makes large-capacity transmission possible. A transmission characteristic is measured in a transmission characteristic measuring section, and control of signal light wavelength in a tunable light source, control of the amount of prechirping, control of the amount of dispersion compensation, and/or control of optical power are performed to achieve the best transmission characteristic. Wavelength dispersion is deliberately introduced by a dispersion compensator, to reduce nonlinear effects. A tunable laser is used to optimize signal light wavelength for each optical amplification repeater section. Peripheral technique, such as drift compensation, clock extraction, optical signal channel identification, clock phase stabilization, etc., are provided for the implementation of optical multiplexing.

Abstract: An apparatus includes a driving voltage generator that generates a pulse driving voltage having a rising edge and a decaying edge. An optical modulator produces a first pulse at the rising edge of the pulse driving voltage and a second pulse at the decaying edge of the pulse driving voltage. Therefore, the first and second pulses are both produced from a single driving pulse voltage. The frequency of the first pulse is determined by the slope of the rising edge of the pulse driving voltage and the frequency of the second pulse is determined by the slope of the decaying edge of the pulse driving voltage. The first and second pulses are transmitted through a transmission line. A detection device detects the first and second pulses after being transmitted through the transmission line.

Abstract: An apparatus includes a driving voltage generator that generates a pulse driving voltage having a rising edge and a decaying edge. An optical modulator produces a first pulse at the rising edge of the pulse driving voltage and a second pulse at the decaying edge of the pulse driving voltage. Therefore, the first and second pulses are both produced from a single driving pulse voltage. The frequency of the first pulse is determined by the slope of the rising edge of the pulse driving voltage and the frequency of the second pulse is determined by the slope of the decaying edge of the pulse driving voltage. The first and second pulses are transmitted through a transmission line. A detection device detects the first and second pulses after being transmitted through the transmission line.