Abstract: In an optical transmitter of the invention, continuous light from a light source is a (CS)RZ-D(Q)PSK modulated by two optical modulators connected in series, and a part of the optical signal output from a post-stage optical modulator is branched by an output monitor section, and the power of a preset frequency component, excluding a frequency component corresponding to a baud rate, included in an electrical spectrum acquired by photoelectrically converting the branched beams is measured. The relative phase of drive signals applied to the optical modulators is then feed-back controlled so that the power becomes a minimum. As a result, a delay shift due to a temperature change or the like between drive signals applied to respective optical modulators, can be reliably compensated.

Abstract: An optical transmission apparatus according to the present invention comprises: a plurality of optical modulating sections serially connected to each other via optical fibers; driving sections corresponding to the optical modulating sections; delay amount varying sections that provide variable delay amounts for modulating signals to be input to the driving sections, to adjust timing between drive signals to be provided for the optical modulating sections; temperature monitoring sections that monitor the temperature of each of the optical fibers and the like; and a delay amount control section that controls the delay amount in each of the delay amount varying sections based on the monitored temperatures.

Abstract: The present invention offers a compensation device having a transmission property for collectively compensating inclinations of accumulated transmission properties in a signal wavelength band of light signals of a plurality of channels configuring a wavelength-multiplexed light, among wavelength dependencies of transmission properties of a plurality of sets of light demultiplexers and light multiplexers.

Abstract: In a chromatic dispersion and dispersion slope compensating apparatus according to the present invention, a WDM light which has been angularly dispersed to a first direction by a VIPA plate, is angularly dispersed to a second direction vertical to the first direction by a diffraction grating, and optical signals of respective wavelengths output from the diffraction grating are reflected by any one of a plurality of three-dimensional mirrors having reflective surfaces of curved shapes different from each other, to be returned to the VIPA plate. Thus, with a simple control mechanism in which the plurality of three-dimensional mirrors are moved to only the second direction, an apparatus capable of variably compensating for the chromatic dispersion and the dispersion slope independent of each other can be provided.

Abstract: A chromatic dispersion monitoring apparatus according to the present invention comprises: a photodetector which photo-electrically converts an optical signal; a low-pass filter which limits a frequency bandwidth of the photo-electrically converted electrical signal to be within a range set according to a modulation format of the optical signal and a bit rate thereof; a DC elimination circuit which eliminates a direct current component of the bandwidth limited electrical signal; and a power detector which detects the power of the bandwidth limited electrical signal to detect the residual dispersion of the optical signal. As a result, it becomes possible to easily realize the chromatic dispersion monitoring apparatus of low cost, which is also capable to be arranged on an in-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 data modulator unit generates a DQPSK optical signal in accordance with a data signal. A phase shift unit provides a phase difference of ?/2 between a pair of arms. A photodetector converts an output signal of the data modulator unit into an electrical signal. A filter is a low-pass filter with a cut-off frequency lower than a symbol frequency, and filters an output signal of the photodetector. A monitor unit detects power of an output signal of the filter. A phase difference control unit adjusts the amount of phase shift in the phase shift unit so as to minimize power of an output signal of the filter.

Abstract: An optical receiving apparatus sets, efficiently and optimally, a delay interferometer and a variable wavelength dispersion compensator in the apparatus.

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 tunable dispersion compensator whose passband center wavelength changes when the amount of dispersion compensation is changed is suitably adjusted. The relationship between temperature for keeping the center wavelength constant and the amount of dispersion compensation is stored in advance. After controlling the amount of dispersion compensation to achieve best or optimum transmission quality, the amount of dispersion compensation is converted into temperature in accordance with the stored relationship and, based on that, the temperature is controlled to keep the center wavelength constant.

Abstract: A phase shift unit provides a prescribed phase difference (?/2, for example) between a pair of optical signals transmitted via a pair of arms constituting a data modulation unit. A low-frequency signal f0 is superimposed on one of the optical signals. A signal of which phase is shifted by ?/2 from the low-frequency signal f0 is superimposed on the other optical signal. A pair of the optical signals is coupled, and a part of which is converted into an electrical signal by a photodiode. 2f0 component contained in the electrical signal is extracted. Bias voltage provided to the phase shift unit is controlled by feedback control so that the 2f0 component becomes the minimum.

Abstract: A phase shift unit provides a prescribed phase difference (?/2, for example) between a pair of optical signals transmitted via a pair of arms constituting a data modulation unit. A low-frequency signal f0 is superimposed on one of the optical signals. A signal of which phase is shifted by ?/2 from the low-frequency signal f0 is superimposed on the other optical signal. A pair of the optical signals is coupled, and a part of which is converted into an electrical signal by a photodiode. 2f0 component contained in the electrical signal is extracted. Bias voltage provided to the phase shift unit is controlled by feedback control so that the 2f0 component becomes the minimum.

Abstract: An optical transmission apparatus includes an optical add drop multiplexer (OADM) that adds/drops an optical signal to/from a transmission path. The optical transmission apparatus further includes a pump light multiplexer and a dispersion compensation fiber that are located downstream of the OADM on the transmission path. The optical transmission apparatus is configured to house a pump light source connectable to the pump light multiplexer to Raman amplify an optical signal in the dispersion compensation fiber.

Abstract: In a chromatic dispersion and dispersion slope compensating apparatus according to the present invention, a WDM light which has been angularly dispersed to a first direction by a VIPA plate, is angularly dispersed to a second direction vertical to the first direction by a diffraction grating, and optical signals of respective wavelengths output from the diffraction grating are reflected by any one of a plurality of three-dimensional mirrors having reflective surfaces of curved shapes different from each other, to be returned to the VIPA plate. Thus, with a simple control mechanism in which the plurality of three-dimensional mirrors are moved to only the second direction, an apparatus capable of variably compensating for the chromatic dispersion and the dispersion slope independent of each other can be provided.

Abstract: An optical transmission system includes a first/second node with a first/second dispersion compensator that performs a first/second dispersion compensation on an optical signal; and a third node that is arranged between the first/second nodes. The amounts of the first/second dispersion compensations are determined so that a cumulative dispersion of the optical signal after the second dispersion compensation is within a predetermined range.

Abstract: The optical node connects N networks to each other (where N is an integer larger than one). Each of the N networks respectively includes a first transmission path and a second transmission path. The optical node includes a switching unit that connects the first transmission path of one network of the N networks to other (N-1) networks; a failure detector that detects failure in the first transmission path of the network; and a control unit that causes the switching unit to connect the second transmission path of the network to the other (N-1) networks when the failure is detected.

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 optical transmitting apparatus is configured such that K pieces of output ports of optical path switching units whose input port is connected to k-th input transmission path are connected to first to K-th output transmission paths except for the k-th output transmission path and to the k-th input port of a dropping unit, and the optical path switching units and the dropping unit outputs light of wavelength which is part or all of WDM light received from said input port from a specific output port, and can output light having a wavelength different from that of the light output from said specific output port from an output port different from said specific output port. Accordingly, while largely reducing the number of optical fiber patch cords necessary in an optical transmitting apparatus and largely reducing the number of spare ports, the flexible expansion of apparatus function can be realized.

Abstract: The optical switch includes: an input port from which beam is input; a dispersing unit that disperses the beam input; a condensing unit that condenses the beam dispersed; a mirror that reflects the beam condensed; and a plurality of output ports from which the beam reflected is output. The mirror rotates around a first axis so that the beam reflected enters one of the output ports, and also rotates around an axis that is selected, according to that which output port the beam reflected enters, from any one of the first axis and a second axis perpendicular to the first axis so that an intensity of the beam output is attenuated.

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.