Abstract: An analog switch circuit that includes a first field-effect transistor, a source of which is coupled to a first switch terminal, and a drain of which is coupled to a second switch terminal; a first capacitance storing electric charge; a second capacitance storing electric charge; a first switch circuit that couples the first capacitance between a direct current voltage node and a reference potential node; a second switch circuit that couples the first capacitance and the second capacitance in parallel; and a third switch circuit that couples the second capacitance between a gate and the source of the first field-effect transistor.

Abstract: A digital analog convertor has a modulator which modulates a digital signal to generate a pulse signal having a pulse density corresponding to a digital value of the digital signal; a first RZ conversion circuit which RZ-converts the pulse signal based on a first clock signal to generate a first RZ pulse signal; a first integration circuit which integrates the first RZ pulse signal to output a first analog signal; a second RZ conversion circuit which RZ-converts a first level signal having a first level of the pulse signal based on the first clock signal to generate a second RZ pulse signal; a second integration circuit which integrates the second RZ pulse signal to output a second analog signal; and a clock duty control circuit which controls a duty ratio of the first clock signal so that the second analog signal approaches a given reference level.

Abstract: An analog switch circuit that includes a first field-effect transistor, a source of which is coupled to a first switch terminal, and a drain of which is coupled to a second switch terminal; a first capacitance storing electric charge; a second capacitance storing electric charge; a first switch circuit that couples the first capacitance between a direct current voltage node and a reference potential node; a second switch circuit that couples the first capacitance and the second capacitance in parallel; and a third switch circuit that couples the second capacitance between a gate and the source of the first field-effect transistor.

Abstract: During a time interval when a supervisory signal is not transmitted, an idle signal which is different in frequency from but substantially equal in maximum power to the supervisory signal is output. The duty ratio of the idle signal is set so that the supervisory signal and the idle signal become substantially equal to each other in average power. A transmitter is equipped with a switcher for switching between the supervisory signal and the idle signal for selective application to a laser diode. The switcher is controlled by a command signal for supervisory and control. The laser diode is driven by an output of the switcher to transmit the supervisory signal and the idle signal.

Abstract: An optical amplifier with redundant excitation light sources for exciting a rare earth doped optical fiber such as an EDF (Erbium Dope Fiber) minimizes the loss of the excitation light so as to introduce the excitation light to the EDF effectively, though an optical coupler, which plural optical fibers for transmitting the excitation lights from plural excitation light sources are welded, is used. And, the optical amplifier keeps the total of the excitation light introduced to the EDF at a predetermined value and changes one excitation light source to the other unless the output total from the respective excitation light sources becomes zero.

Abstract: An optical amplifier with redundant excitation light sources for exciting a rare earth doped optical fiber such as an EDF (Erbium Dope Fiber) minimizes the loss of the excitation light so as to introduce the excitation light to the EDF effectively, though an optical coupler, which plural optical fibers for transmitting the excitation lights from plural excitation light sources are welded, is used. And, the optical amplifier keeps the total of the excitation light introduced to the EDF at a predetermined value and changes one excitation light source to the other unless the output total from the respective excitation light sources becomes zero.

Abstract: An optical repeater is provided between terminal stations and amplifies optical signals that have entered via optical fibers in upward and downward directions and outputs the amplified optical signals to optical fibers in respective directions. The optical fiber on the output side of an upward optical amplifier and the optical fiber on the output side of a downward optical amplifier are optically coupled, with a prescribed loss, by a photocoupler. The upward optical signal is looped back to the optical fiber in the downward direction upon being attenuated by, say, 40 dB via the photocoupler, and the downward optical signal is looped back to the optical fiber in the upward direction upon being attenuated by, say, 40 dB, via the photocoupler.

Abstract: An optical repeater OFF-state supervisory method includes the steps of: converting an input optical signal into an electrical signal; monitoring a level of the input optical signal from a monitored value when converted into the electrical signal; monitoring whether an input optical signal to an optical repeater is in an OFF state or not; detecting that the input optical signal has been in an OFF state; and changing the monitored value to a predetermined fixed monitored value.

Abstract: An optical repeater provided in an up line and a down line, the optical repeater includes a first circuit related to the up line, and a second circuit related to the down line. Each circuit includes an optical receive/decision circuit, a command extraction circuit, a command detection circuit, a command switch and a supervisory circuit. Each circuit also includes a noise component processing circuit which extracts, from the electrical signal, a noise component within a predetermined frequency range excluding a frequency of the command signal and determines whether or not the optical signal is input to the optical receive/decision circuit on the basis of the noise component and which prevents the noise component passing through the command extracting circuit from being directly applied to the command detecting circuit when it is determined that no the optical input is input to the optical receive/decision circuit.

Abstract: An optical repeater includes a first converter converting an optical input signal into an electrical signal, an equalizing amplifier which amplifies the electrical signal and which outputs an amplified electrical signal, and a timing extraction circuit which extracts a timing signal from the amplified electrical signal. Also the optical repeater includes a phase inversion circuit which receives the amplified electrical signal in synchronism with the timing signal and which outputs a phase-inverted signal in synchronism with the timing signal. The phase-inverted signal has a phase opposite to a phase of the amplified electrical signal. Further, the optical repeater includes a second converter having a diffused laser diode and converting the phase-inverted signal into an optical output signal, and a supervisory signal extraction circuit which extracts a supervisory signal contained in the optical input signal from the phase-inverted signal.

Abstract: A phase shift circuit includes a first trailing-edge elongating circuit that elongates a trailing edge of each pulse of an input clock signal so as to fall gradually and outputs a first clock signal having a first elongated fall time. A signal inversion circuit inverts the first clock signal supplied from the first trailing-edge elongating circuit and outputs an inverted version of the first clock signal. A second trailing-edge elongating circuit elongates a trailing edge of each pulse of the inverted version of the first clock signal so as to fall gradually and outputs a second clock signal having a second elongated fall time. The second clock signal is an output signal of the phase shift circuit and lags behind the input clock signal by a predetermined time based on the first and second elongated fall times. The present invention further provides a repeater which uses the above-mentioned phase shift circuit.

Abstract: A submarine optical cable provided with optical repeaters and the like is spirally wound as a coil in a cable tank having a wall which defines at least a part of a cable storing space in which the cable is accommodated and is parallel to an axis of the coiled optical cable. A metal plate is provided along and covering an entire peripheral region of the wall to counterbalance induced voltage generated in the coiled optical cable.