Abstract: An optical receiving circuit 1 is composed of a preamplifier circuit 2, an output differential amplifier 3 and a mean value holding circuit 4. The optical receiving circuit 1 is connected to a photodetector 5 for receiving an input optical signal and outputting current. For the preamplifier circuit 2, a transimpedance type circuit may also be used. The preamplifier circuit 2 comprises a feedback resistor 21 and a resistor for detecting output voltage 22, the transimpedance gain is 55 dB &OHgr; and 3 dB bandwidth when the photodetector 5 the capacity of which is 0.2 pF is connected to its output is 8 GHz. The output differential amplifier 3 discriminates and regenerates data by regulating reference voltage Vref between the high level and the low level of the amplitude of an input signal. The mean value holding circuit 4 includes a sample-hold circuit 41 and capacity 42 for holding the mean value of voltage output from the preamplifier circuit 2.

Abstract: A packet switching network which allows the duration of guard time of each packet to be reduced to a minimum and the transmission efficiency of the network to be increased is disclosed. The sending nodes send the packet switch packets each having a guard time added thereto. The receiving nodes receive the packets from the packet switch. Each of the receiving nodes includes a switch timing detector for detecting switch timing of the packet switch based on a serial signal received from the packet switch, and a timing holder for holding the switch timing.

Abstract: In a method of controlling a switching operation of an optical network for use in connection between an optical transmitter and an optical receiver through an optical switch is controlled by a switch controller, the optical receiver is given through the optical switch a sequence of combined optical signals which is formed by combining a sequence of optical signals with an additional sequence of optical signals. The additional sequence of the optical signals may be either a sequence of optical signals sent to another optical receiver or a sequence of dummy optical signals. The combined optical signal sequence has a time interval which is defined between two adjacent ones of the combined optical signals and which is shorter than a predetermined time interval of, for example, 1 millisecond. Such a combined optical signal sequence serves to avoid occurrence of an optical surge appearing when the time interval is longer than the predetermined time interval.

Abstract: The objectives of this invention are to provide a novel Nile Red luminescent compound capable of emitting a light of which color is nearly crimson, a novel process for producing the same and a luminescent compound capable of emitting at a high luminance a nearly crimson light. This invention relates to a Nile Red luminescent compound emitting red light made by changing C═O in a Nile Red compound to C═CH—Ar, wherein Ar is an aromatic group including fluorine atoms, and by introducing an electron attractive aromatic acetonitrile into the skeleton of the Nile Red compound; a novel process for producing the Nile Red luminescent compound that comprises reacting a Nile Red pigment with an electron attractive aromatic acetonitrile, and a luminescent compound comprising a composition that includes the Nile Red luminescent compound.

Abstract: An optical network system is provided which has a signal protection function and is able to be constructed of communication nodes manufactured at low costs. An optical signal transceiver has at least one optical signal transmitting device and at least one optical signal receiving device to transmit and receive an optical signal between nodes facing each other. A switching device, when no failure has occurred in the optical signal transmitting communication line and optical signal receiving communication line, transmits an optical signal from the optical signal transmitting device to an optical signal transmitting communication line and an optical signal having been received from the optical signal receiving communication line to an optical signal receiving device.

Abstract: A system and method for bidirectional optical transmission in one optical fiber with large transmission capacity, enabling the enlargement of transmission distance. Downward optical signals sent from one or more downward optical signal transmitters are received by one or more downward optical signal receivers via an optical fiber transmission line and upward/downward signal separating multiplexer—demultiplexers. On the other hand, upward optical signals sent from one or more upward optical signal transmitters are received by one or more upward optical signal receivers by following the opposite route. Output signals from the downward optical signal transmitter leak in the upward optical signal receiver via the upward/downward signal separating multiplexer—demultiplexer.

Abstract: An optical packet exchange apparatus and an optical switch in which search for a connection pattern between an input unit devoid of a packet to be transmitted and an output unit devoid of a packet to be received is reduced to enable fast switch control even in cases wherein the number of channels of the exchange apparatus is increased or network speed is higher. A plurality of input units, a plurality of output units and an optical switch are provided. Each input unit includes an input buffer unit, a parallel/serial conversion unit, an electrical/optical conversion unit, and a dummy packet insertion unit for sending a dummy packet if there is no packet to be transmitted. Each output unit includes an exchange counterpart contention resolution unit for controlling the exchange counterpart, an optical/electrical conversion unit, a serial/parallel conversion unit, and a packet eliminating unit. The exchange counterpart contention resolution unit controls the packet eliminating unit to eliminate a dummy packet.

Abstract: A wavelength division-multiplexing system is provided that uses wavelength grids in conformity with the ITU-T Recommendation G.692 and that is realizable at lower costs. In the system, the wavelengths of signal light beams transmitted from plural optical transmitters are respectively spaced apart in such a manner that multiplexed wavelengths are set at regular intervals within the band range of the optical amplifier 5. The wavelength range of each laser beam covers at least two grids including neighboring grids. The wavelength demultiplexer 3 on the receiving side has the passband passing the wavelengths in a laser wavelength range corresponding to each channel.

Abstract: The objective of this invention is to provide fluorescent compounds comprising a naphthalene skeleton, an electron donating group substituted at the 2- or 1-position of the naphthalene skeleton, and an electron attractive group substituted at the 6- or 4-position of the skeleton. The fluorescent compound of this invention is capable of emitting visible light having a desired color by choosing an appropriate combination of the electron donating group A, which has an electron-pushing function, and the electron attractive group B, which has an electron-pulling function.

Abstract: The object of this invention is to provide an illuminant, which can easily be produced at low cost. This invention is a carbazole derivative luminescent compound having a carbazole ring skeleton, to the nitrogen atom of which is attached an electron-donating group, and to the carbon atom of which is attached an electron-attracting group at the third position to the nitrogen atom.

Abstract: The object of this invention is to provide an illuminant, which can easily be produced at low cost. This invention is a carbazole derivative luminescent compound having a carbazole ring skeleton, to the nitrogen atom of which is attached an electron-donating group, and to the carbon atom of which is attached an electron-attracting group at the third position to the nitrogen atom.

Abstract: The objective of this invention is to provide fluorescent compounds comprising a naphthalene skeleton, an electron donating group substituted at the 2- or 1-position of the naphthalene skeleton, and an electron attractive group substituted at the 6- or 4-position of the skeleton. The fluorescent compound of this invention is capable of emitting visible light having a desired color by choosing an appropriate combination of the electron donating group A, which has an electron-pushing function, and the electron attractive group B, which has an electron-pulling function.

Abstract: An optical packet exchange apparatus and an optical switch in which search for a connection pattern between an input unit devoid of a packet to be transmitted and an output unit devoid of a packet to be received is reduced to enable fast switch control even in cases wherein the number of channels of the exchange apparatus is increased or network speed is higher. A plurality of input units, a plurality of output units and an optical switch are provided. Each input unit includes an input buffer unit, a parallel/serial conversion unit, an electrical/optical conversion unit, and a dummy packet insertion unit for sending a dummy packet if there is no packet to be transmitted. Each output unit includes an exchange counterpart contention resolution unit for controlling the exchange counterpart, an optical/electrical conversion unit, a serial/parallel conversion unit, and a packet eliminating unit. The exchange counterpart contention resolution unit controls the packet eliminating unit to eliminate a dummy packet.

Abstract: An optical packet exchange apparatus and an optical switch in which search for a connection pattern between an input unit devoid of a packet to be transmitted and an output unit devoid of a packet to be received is reduced to enable fast switch control even in cases wherein the number of channels of the exchange apparatus is increased or network speed is higher. A plurality of input units, a plurality of output units and an optical switch are provided. Each input unit includes an input buffer unit, a parallel/serial conversion unit, an electrical/optical conversion unit, and a dummy packet insertion unit for sending a dummy packet if there is no packet to be transmitted. Each output unit includes an exchange counterpart contention resolution unit for controlling the exchange counterpart, an optical/electrical conversion unit, a serial/parallel conversion unit, and a packet eliminating unit. The exchange counterpart contention resolution unit controls the packet eliminating unit to eliminate a dummy packet.

Abstract: An optical packet exchange apparatus and an optical switch in which search for a connection pattern between an input unit devoid of a packet to be transmitted and an output unit devoid of a packet to be received is reduced to enable fast switch control even in cases wherein the number of channels of the exchange apparatus is increased or network speed is higher. A plurality of input units, a plurality of output units and an optical switch are provided. Each input unit includes an input buffer unit, a parallel/serial conversion unit, an electrical/optical conversion unit, and a dummy packet insertion unit for sending a dummy packet if there is no packet to be transmitted. Each output unit includes an exchange counterpart contention resolution unit for controlling the exchange counterpart, an optical/electrical conversion unit, a serial/parallel conversion unit, and a packet eliminating unit. The exchange counterpart contention resolution unit controls the packet eliminating unit to eliminate a dummy packet.

Abstract: Disclosed is an optical network which has: wavelength tunable optical transmitters of number MN, where N is an integer of two or more, each of which outputs an optical signal with arbitrary one of M wavelengths &lgr;1, &lgr;2, . . . , &lgr;M, where M is an integer of two or more, that are different from one another; a MN×N optical switch whose input ports are connected to the respective wavelength tunable optical transmitters of number MN, and which allows optical signals input to different input ports to be output form its same output port; 1×M optical wavelength demultiplexers of number N which output demultiplexing optical signal with wavelengths &lgr;1, &lgr;2, . . . , &lgr;M input from output ports of the MN×N optical switch into each wavelength; and optical receivers of number MN which receive optical signals input from the 1×M optical wavelength demultiplexers of number N.

Abstract: A bit synchronization circuit operates at high speed range as high as Gb/s or higher and can establish synchronization within 10 bits with rejecting jitter to permit accurate bit synchronization. The bit synchronization circuit thus generates a plurality of clocks having mutually different phases in synchronism with an input reference clock. A phase relationship between a plurality of clocks and an input data to be decided is discriminated by a phase comparator circuit. The clock having optimal phase relationship, namely clock having level transition timing having at a substantially center portion of mutually adjacent level transition timing of the input data, is determined by a phase determination circuit. An decision circuit and selector are provided for deciding input data at the level transition timing of the determined clock.

Abstract: In a method of controlling a switching operation of an optical network for use in connection between an optical transmitter and an optical receiver through an optical switch is controlled by a switch controller, the optical receiver is given through the optical switch a sequence of combined optical signals which is formed by combining a sequence of optical signals with an additional sequence of optical signals. The additional sequence of the optical signals may be either a sequence of optical signals sent to another optical receiver or a sequence of dummy optical signals. The combined optical signal sequence has a time interval which is defined between two adjacent ones of the combined optical signals and which is shorter than a predetermined time interval of, for example, 1 millisecond. Such a combined optical signal sequence serves to avoid occurrence of an optical surge appearing when the time interval is longer than the predetermined time interval.

Abstract: In a method of controlling a switching operation of an optical network for use in connection between an optical transmitter and an optical receiver through an optical switch is controlled by a switch controller, the optical receiver is given through the optical switch a sequence of combined optical signals which is formed by combining a sequence of optical signals with an additional sequence of optical signals. The additional sequence of the optical signals may be either a sequence of optical signals sent to another optical receiver or a sequence of dummy optical signals. The combined optical signal sequence has a time interval which is defined between two adjacent ones of the combined optical signals and which is shorter than a predetermined time interval of, for example, 1 millisecond. Such a combined optical signal sequence serves to avoid occurrence of an optical surge appearing when the time interval is longer than the predetermined time interval.

Abstract: A clock extraction circuit which is simplified in structure, improved in transmission efficiency, amenable to integration and size reduction and not limited by the operating speed of a phase comparator. An input signal frequency-divided by m and extracted clock signals outputted by a voltage-controlled oscillator and frequency-divided by n are phase-compared and an absolute value of the output of the phase comparator is taken by an absolute value circuit. An output of the absolute value circuit is passed through a low-pass filter to control the voltage-controlled oscillator for constituting the clock extraction circuit.