Abstract: A four fiber ring network optical switching circuit capable of realizing the bridge function at times of the span switching and the ring switching economically by a very compact structure is disclosed. A four fiber ring network optical switching circuit is formed by a 10×8 optical matrix switch having ten input ports and eight output ports, and two branching elements adapted to branch each one of two optical signals among eight optical signals that are inputs of the four fiber ring network optical switching circuit, into two identical optical signals, and to enter the two identical optical signals into two input ports of the 10×8 optical matrix switch such that the eight optical signals are entered into the ten input ports of the 10×8 optical matrix switch as ten optical signals.

Abstract: Signal light (at a wavelength &lgr;s), entered an input terminal from an optical transmission line, inputs a combiner through an optical amplifier. The combiner combines the output light of the optical amplifier and the probe light (at a wavelength &lgr;p) from a probe light source and applies them to an EA modulator. The EA modulator superimposes a waveform of the signal light on the probe light. An optical BPF transmits only the component of the probe wavelength &lgr;p in the output light of the EA modulator. A photodetector converts the output light of the optical BPF into an electric signal, and an amplifier electrically amplifies the output of the photodetector. A BPF extracts the clock component of the input signal light from the output of the amplifier and applies it to a driver. The driver pulsatively drives the probe light source at the same frequency with that of the clock signal from the BPF and adjusts its pulse phase so as to synchronize with the current pulse from the EA modulator.

Abstract: In a signal demultiplexing device formed by a probe light source, a wavelength converter, and a wavelength demultiplexer, the probe light source is formed by a plurality of sub-probe light sources configured to respectively generate the sub-probe lights with the prescribed different wavelengths for respective time-slots, a multiplexer configured to multiplex the sub-probe lights generated by the plurality of sub-probe light sources, and a phase different giving unit configured to give phase differences corresponding to time-slot positions to the sub-probe lights multiplexed by the multiplexer, and to sequentially output the sub-probe lights with the phase differences in correspondence to respective time-slots.

Abstract: An optical clock multiplier comprises a phase modulator (12) to shift a phase in pulse duration of an input optical clock pulse by &pgr;, a polarization mode dispersion device (16) having a predetermined time difference between first and second polarizations orthogonal to each other to divide an output light from the phase modulator into the first and second polarization components, and a polarization device (20) to extract one of polarization components in a third polarization practically inclined at an angle of 45° against the first polarization and a fourth polarization orthogonal to the third polarization out of the output light from the polarization mode dispersion device.

Abstract: A data/audio multiplex transmission system comprising an audio modulator to modulate an input audio signal and output the modulated audio signal, an optical pulse signal generator to generate an optical pulse signal for carrying a LAN data, amplitude of the optical pulse signal being modulated by the modulated audio signal, according to the LAN data and the modulated audio signal, an optical fiber to propagate the optical signal output from the optical pulse signal generator, an opto-electric converter to convert the optical signal propagated on the optical fiber into an electric signal, a filter to extract a predetermined band out of the output signal from the opto-electric converter, an audio demodulator to demodulate the audio signal out of the output from the filter, and a data transmitter to transmit the LAN data included in the output signal from the opto-electric converter for a LAN.

Abstract: To realize a highly reliable monitor control signal network at low costs, a data transmission system comprises a first network to optically transmit a data signal and a monitor control signal, first and second nodes connecting to the first network, and a second network capable of transmitting the monitor control signal.

Abstract: An optical digital regenerator for digitally regenerating an input signal in an intact optical state. A first operating unit has a first probe light generator for generating a first probe light and a first optical operator for converting a waveform of the first probe light output from a first probe light generator according to an optical intensity waveform of the input signal light. A clock extractor extracts a clock component of the input signal light from a photocurrent generated by the first optical operator. A second optical operating unit has a second probe light generator for generating a second probe light pulsed in accordance with the clock output from the clock extractor and a second optical operator for sampling the second probe pulse light output from the second probe light generator.

Abstract: An optical reception apparatus comprises an optical receiver to receive an optical signal from an optical transmission line, an error corrector to correct an error of the signal received by the optical receiver and to transmit the error-corrected signal and error rate information before error correction, a judging apparatus to judge transmission quality of the optical transmission line according to the error rate information from the error corrector and a threshold value equal to an error rate lower than an error correction limit of the error corrector, and a selective breaker to transmit the signal whose error is corrected by the error corrector in normal state and to block transmission of the signal whose error is corrected by the error corrector when the judged result by the judging apparatus indicates deterioration of the transmission quality of the optical transmission line.

Abstract: An optical crossconnect system comprises an input stage including a plurality of input matrix switches, each having a plurality of input ports and a plurality of output ports, an output stage including a plurality of output matrix switches, each having a plurality of input ports and a plurality of output ports, and an intermediate stage including a plurality of intermediate matrix switches, each having a plurality of input ports and a plurality of output ports. Each input port of each intermediate matrix switch connects to an output port which corresponds to the intermediate matrix switch, at an input matrix switch corresponding to the input port in the plurality of input matrix switches. Each output port of each intermediate matrix switch connects to an input port, which corresponds to the intermediate matrix switch, at an output matrix switch corresponding to the output port in the plurality of output matrix switches.

Abstract: An object of this invention is to regenerate optical signals in an intact optical state according to a low-speed optical clock.

Abstract: A four fiber ring network optical switching circuit capable of realizing the bridge function at times of the span switching and the ring switching economically by a very compact structure is disclosed. A four fiber ring network optical switching circuit is formed by a 10×8 optical matrix switch having ten input ports and eight output ports, and two branching elements adapted to branch each one of two optical signals among eight optical signals that are inputs of the four fiber ring network optical switching circuit, into two identical optical signals, and to enter the two identical optical signals into two input ports of the 10×8 optical matrix switch such that the eight optical signals are entered into the ten input ports of the 10×8 optical matrix switch as ten optical signals.

Abstract: A network system capable of delivering a large amount of data such as video data freely according to the intentions of the sender and the receiver alone is realized by a plurality of stations provided on at least one loop shaped optical network in which any one of the plurality of stations is capable of carrying out unidirectional communications with respect to any other one of the plurality of stations, where at least one wavelength is allocated to each station such that each station can transmit data by using a wavelength allocated to each station, receive data of any wavelengths transmitted from any other stations, and select only necessary wavelengths so as to select correspondent stations from which data are to be received.

Abstract: In an optical transmission system, an optical transmission line has up and down systems and loops back a supervisory light between the up and down systems. Trunk stations are provided at both ends of the optical transmission line and one or more optically branching units are provided in the optical transmission line for add/dropping a specific wavelength respectively. A branch station is connected to each of one or more the branching units. A bypass line for bypassing the supervisory light is provided in each of the one or more optically branching units.

Abstract: In a signal demultiplexing device formed by a probe light source, a wavelength converter, and a wavelength demultiplexer, the probe light source is formed by a plurality of sub-probe light sources configured to respectively generate the sub-probe lights with the prescribed different wavelengths for respective time-slots, a multiplexer configured to multiplex the sub-probe lights generated by the plurality of sub-probe light sources, and a phase different giving unit configured to give phase differences corresponding to time-slot positions to the sub-probe lights multiplexed by the multiplexer, and to sequentially output the sub-probe lights with the phase differences in correspondence to respective time-slots.

Abstract: A demultiplexer device is used in a wavelength-division multiplexed optical fiber communication line to achieve efficient dispersion compensation and loss compensation as well as a reduction of active devices such as optical amplifiers. The demultiplexer device has a series of couplers disposed in multi-stages from the input of the demultiplexer. Each coupler has two branches with one branch of each coupler connected to a separate optical filter and the other branches are series connected to a subsequent stage of the couplers through equalizing fibers, except for the final stage which has its second branch connected to an optical filter for the shortest wavelength transmitted. The equalizing fibers are thus serially connected between couplers and act to perform a cumulative dispersion compensation. The quantity of the equalizing fibers can thus be reduced as a whole, and as a result the attenuation amount also decreases, so that the number of optical amplifiers can be reduced.

Abstract: A method of suppressing noise and improving the optical transmission characteristic of a wavelength division multiplexing transmission system provides lights for suppressing noise from the light sources (NS1 and NS2) which are multiplexed on the wavelength division multiplexed signal. Consequently, the S/N ratio of each channel of a wavelength division multiplexed signal which propagates through the optical path can be improved.