Abstract: An optical communication apparatus, in the sending side, distributes client signals according to destinations and a communication capacity of each destination, electrical-to-optical converts the distributed signals to optical signals having different center frequencies, and multiplexes the optical signals to output, and in the receiving side, the optical communication apparatus divides the wavelength division multiplexed signal to each wavelength (for each sending source), optical-to-electrical converts the divided optical signals to electrical signals, and multiplexes the electrical signals to output. An add/drop port of an optical route switching apparatus includes an input/output port to the optical communication apparatus, and an optical frequency bandwidth is variable according to an optical spectrum width of the optical signal. A network is constructed by using the optical communication apparatus and the optical route switching apparatus.

Abstract: A multi-flow optical transceiver provided with a plurality of wavelength-tunable light sources, a plurality of optical modulation units which modulates light with an input signal, an optical multiplexing/demultiplexing switch which couples light from at least one of the wavelength-tunable light sources to at least one of the optical modulation units with any power, and an optical coupling unit which couples a plurality of lights, modulated by a plurality of the optical modulation units, to at least one waveguide.

Abstract: A bandwidth variable communication apparatus includes: a route exchange unit including a route exchange function for switching an output port of a stream signal of one or more wavelengths input from an input port based on both or a part of wavelength and time, and including a bandwidth change function for changing passable frequency bandwidth in a section from the input port to the output port through which the stream signal passes; and a control unit including a control information transmit-receive function for transmitting and receiving control information for both or a part of the route exchange function and the bandwidth change function of the route exchange unit, and including a control function for controlling the route exchange unit based on the control information. All or a part of the input ports and the output ports are connected to other communication apparatuses via transmission routes.

Abstract: A bandwidth variable communication method is provided that enables effective use of frequency bandwidths in which the bit rate is constant in every optical path. The bandwidth variable communication method includes, when a network management apparatus sets or changes an optical path that passes through plural communication apparatuses, measuring or obtaining an optical signal quality deterioration amount in a route of the optical path; selecting a modulation format in which a spectrum bandwidth is the narrowest from among modulation formats by which transmission is available on conditions of the optical signal quality deterioration amount and a desired bit rate B (bit/s); and exchanging control information between the network management apparatus and a control unit of each communication apparatus on the optical path route. A bandwidth variable communication apparatus receives the control information, and changes a passband based on the received control information.

Abstract: A bandwidth variable communication apparatus includes: a route exchange unit including a route exchange function for switching an output port of a stream signal of one or more wavelengths input from an input port based on both or a part of wavelength and time, and including a bandwidth change function for changing passable frequency bandwidth in a section from the input port to the output port through which the stream signal passes; and a control unit including a control information transmit-receive function for transmitting and receiving control information for both or a part of the route exchange function and the bandwidth change function of the route exchange unit, and including a control function for controlling the route exchange unit based on the control information. All or a part of the input ports and the output ports are connected to other communication apparatuses via transmission routes.

Abstract: The present invention provides an optical signal quality monitoring circuit and an optical signal quality monitoring method for measuring correct optical signal quality parameters when a signal bit rate is changed. The optical signal quality monitoring circuit which samples and converts an electrical signal converted from an optical signal with a given repeated frequency f1 to digital sampling data through an analog to digital conversion, thereafter, evaluates an optical signal quality parameter of the optical signal by subjecting sampling data to electrical signal processing in an integrated circuit in which a signal processing function is programmed, receives a control signal notifying that the bit rate of the optical signal is changed, or detects that the bit rate of the optical signal is changed to correct optical the signal quality parameter of the optical signal corresponding to the signal bit rate of the optical signal which is changed.

Abstract: In a wavelength division multiplexing optical transmission system, in order to know an influence amount of a temperature dependency of a dispersion slope, a method of monitoring a dispersion variation amount in two or more of wavelength channels is provided. Further, a method of compensating a wavelength dependency of a temperature dependency of the dispersion by providing an appropriate dispersion individually to the channels or summarizingly for all of bandwidths based on the monitored dispersion variation amounts is provided. According to the present invention, in the WDM optical transmission system, a deterioration in a transmission characteristic by influence of a temperature variation of the dispersion slope can be reduced.

Abstract: The present invention provides an optical signal quality monitoring circuit and an optical signal quality monitoring method for measuring correct optical signal quality parameters when a signal bit rate is changed. The optical signal quality monitoring circuit which samples and converts an electrical signal converted from an optical signal with a given repeated frequency f1 to digital sampling data through an analog to digital conversion, thereafter, evaluates an optical signal quality parameter of the optical signal by subjecting sampling data to electrical signal processing in an integrated circuit in which a signal processing function is programmed, receives a control signal notifying that the bit rate of the optical signal is changed, or detects that the bit rate of the optical signal is changed to correct optical the signal quality parameter of the optical signal corresponding to the signal bit rate of the optical signal which is changed.

Abstract: In a wavelength division multiplexing optical transmission system, in order to know an influence amount of a temperature dependency of a dispersion slope, a method of monitoring a dispersion variation amount in two or more of wavelength channels is provided. Further, a method of compensating a wavelength dependency of a temperature dependency of the dispersion by providing an appropriate dispersion individually to the channels or summarizingly for all of bandwidths based on the monitored dispersion variation amounts is provided. According to the present invention, in the WDM optical transmission system, a deterioration in a transmission characteristic by influence of a temperature variation of the dispersion slope can be reduced.

Abstract: A monitoring system includes first and second evaluation sections for obtaining an averaged Q-factor parameter and a waveform distortion parameter from an optical signal amplitude histogram collected from optical signals under measurement. The monitoring system further includes a third evaluation section for determining both averaged Q-factor parameter and waveform distortion parameter, and for making a decision as to whether the main factor of the optical signal quality degradation is waveform distortion or not by comparing the averaged Q-factor parameter and waveform distortion parameter with their initial values or initial characteristics which are obtained when no optical signal quality degradation is present.

Abstract: The scale and complexity of an apparatus is reduced by omitting a clock extraction section. The apparatus includes: a sampling pulse train generation device which generates an optical or electrical sampling pulse train, independently of an input optical or electrical data signal with a bit rate f0(bit/s), and which has a repetition frequency f1(Hz); a data signal sampling device which samples the data signal in accordance with the sampling pulse train to obtain a sampled signal; a voltage retaining device which converts the sampled signal, and stores pieces of electrical digital data; an electrical signal processing device which reads the digital data at once or sequentially to obtain a signal eye-diagram and evaluates optical data signal quality parameters; and a trigger signal generation device which applies triggers indicating the start/finish of data acquisition and data read to the voltage retaining device and the electrical signal processing device, respectively.

Abstract: This optical clock phase-locked loop circuit includes an oscillator 12, an optical coupler 2, an optical cross-correlation detection device 3 that outputs light containing the correlating components of two lights from the coupled light of optical coupler 2, an optical band pass filter 4 that extracts light of a wavelength that contains cross-correlating components, an optical receiver 5, a phase comparator 6 that compares the phases of the output signal of the oscillator 12 and the cross-correlation signal from the optical receiver 5, a voltage controlled oscillator 7 that changes the oscillation frequency and phase corresponding to the output of the phase comparator 6, an optical pulse generator 8 that generates a optical clock pulse containing an nth harmonic component, an optical coupler 10 that divides optical clock, and an optical modulator 11 driven by low-frequency oscillator 12 that modulates optical clock from optical coupler 10.

Abstract: An optical signal quality degradation monitoring apparatus for monitoring an optical wavelength division multiplex signal is implemented in a small size. To monitor the optical signal quality degradation in the optical wavelength division multiplex signal by a configuration as simple as possible, the following configurations are used: A configuration using an optical wavelength division demultiplexer and a sampling clock generator to make one an electric signal processor; A configuration using an optical sampling pulse train generator, an optical multiplexer, a nonlinear optical medium, and an optical wavelength division demultiplexer to make one an electric signal processor; or a configuration using a selection wavelength control section, an optical wavelength selecting section, and a sampling clock generator to make one electric signal.

Abstract: In an ultrahigh-speed clock extraction circuit wherein a local pulse generating light source 22 for generating a local optical pulse stream synchronized in bit phase with an input optical signal pulse stream is placed in a phase-locked loop, when repetition frequencies of the input optical signal pulse stream and the local optical pulse stream bear a particular relationship, a frequency demultiplier 32 and multipliers 43 and 52 are set so that the frequency of a modulation signal for an optical modulator 41 and a frequency which is a natural-number multiple of the modulation signal frequency, and the frequency of a down-converted version of an optical pulse stream output from a photodetector 42 differ from each other.

Abstract: An optical modulation/multiplexing circuit can fabricate a plurality of nonlinear optical waveguide devices and silica optical waveguides through a small number of processes, and achieve the simplification of the fabrication process and stabilization of the operation by hybrid integration with reduced connection loss. It employs lithium niobate domain inversion optical waveguides as nonlinear optical switches, and implements functions necessary for modulation and multiplexing such as input, splitting, multiplexing and timing adjustment of optical modulation signals and an optical clock signal by connecting glass waveguides to the input and output terminals of the domain inversion optical waveguides. Nonlinear optical media generate a second harmonic light beam of the optical clock signal, and at the same time produces a light beam with a frequency corresponding to the difference frequency of the two high frequency signals, the second harmonic light beam and the signal pulses.

Abstract: A nonlinear optical crystal is composed of 2-adamantyl-5-nitorpyridine (AANP) allowing the type 2 phase matching to the sampling light and a measuring object light, emitting a sum frequency light of the measuring object light and the sampling light, with the polarization directions thereof being perpendicular to each other, when the sampling light and measuring object light multiplexed by a multiplexer are entered. When the sum frequency light is emitted through the nonlinear optical crystal, a control portion controls the polarization direction of the sampling light so as to be parallel to a predetermined reference axis located within a plane perpendicular to a phase matching direction of the nonlinear optical crystal. The predetermined reference axis is a single axis maintaining parallelism with the crystal axis of the nonlinear optical crystal even if the wavelength of the inputted light is changed.

Abstract: A nonlinear optical crystal allowing type 2 phase matching multiplexes a fixed wavelength light having an angular frequency &ohgr;D and a variable wavelength light having an angular frequency &ohgr;S, with the polarization directions thereof being perpendicular to each other, so as to produce a sum frequency light having an angular frequency &ohgr;D+&ohgr;S. When multiplexing the fixed wavelength light and the variable wavelength light through the nonlinear optical crystal, a controlling section controls the polarization direction of the fixed wavelength light so as to be parallel to a predetermined reference axis within a plane vertical to a phase matching direction of the nonlinear optical crystal. Even when the wavelength of inputted light is changed, the predetermined reference axis is a single axis which maintains parallelism with the crystal axis of the nonlinear optical crystal.

Abstract: Signal channels are identified easily by uniquely correlating the port numbers of the optical time-division-demultiplexing unit with channel numbers. The extraction apparatus includes an optical time-division-demultiplexing unit that separates multiplexed signals into N channels and provides them to N separate ports, a channel extraction unit that is connected to N separate ports and extracts one channel number of the N channels, a channel switch that switches the N channels to the output ports of which port numbers uniquely match with the numbers of the N channels based on the relationship between the number of the one channel extracted and the output port number corresponding to the one channel number, and a data output unit that has N output ports and provides the signals of the switched N channels to the output ports of which port numbers match with the channel numbers.

Abstract: The scale and complexity of an apparatus is reduced by omitting a clock extraction section. The apparatus includes: a sampling pulse train generation device which generates an optical or electrical sampling pulse train, independently of an input optical or electrical data signal with a bit rate f0 (bit/s), and which has a repetition frequency f1 (Hz); a data signal sampling device which samples the data signal in accordance with the sampling pulse train to obtain a sampled signal; a voltage retaining device which converts the sampled signal, and stores pieces of electrical digital data; an electrical signal processing device which reads the digital data at once or sequentially to obtain a signal eye-diagram and evaluates optical data signal quality parameters; and a trigger signal generation device which applies triggers indicating the start/finish of data acquisition and data read to the voltage retaining device and the electrical signal processing device. respectively.

Abstract: An optical fiber, capable of generating by means of nonlinear phenomena, white light in adequately broadened wavelength bands at both sides of a pumping optical pulse that is input, and stabilizing the polarized conditions. The fiber is formed by covering a core with a first cladding, and covering the first cladding with a second cladding, where the second cladding has a refractive index greater than that of the first cladding, but lower than that of the core. Stress-applying parts are provided inside the second cladding so as to sandwich the core from both sides to form a polarization-maintaining optical fiber. The shortest distance between the stress-applying parts is made 2.3 times or more the mode field diameter for the wavelength of the pumping optical pulse.