Fujitsu Corporation

Tetsuya Kiyonaga

Terumi Chikama

Motoyoshi Sekiya

Shigeki Watanabe

Takao Naito

Yoshihito Onoda

Setsuo Misaizu

Hisaya Sakamoto

Akihiko Sugata

Akimitsu Miyazaki

Hideo Kuwahara

Hiroshi Onaka

Yasunori Nagakubo

Nobuaki Sato

Mitsuharu Noda

Yoshitaka Shimura

Hiroyuki Furukawa

George Ishikawa

Hideyuki Miyata

Naoki Kuwata

Yuka Kobayashi

Tetsuo Watanabe

Hiroshi Nakamoto

Noriaki Mizuguchi

Tatsuro Kunikane

Yasuhide Kuroda

Yoshimitsu Sakai

Norio Nagase

Sadayuki Miyata

Takeo Iwama

Tomoyuki Otsuka

Makoto Totani

Tetsuji Sato

Takayoshi Tanemura

Takashi Kurooka

Hiroshi Kuwahara

Masaki Ono

Chiaki Ohsawa

An optical transmitter device capable of high-speed shutdown of optical output. A bias controller generates a low-frequency signal, extracts the frequency component of a low-frequency signal from an electrical signal fed back thereto, and compares the phase of the frequency component of the low-frequency signal generated thereby with that of the frequency component of the extracted low-frequency signal, to generate a direct-current voltage with which the operating point of an optical modulator is optimized. Using a half-wave voltage of the optical modulator and an optimum voltage, a bottom voltage calculation unit calculates a bottom voltage corresponding to a minimum of the operation characteristic curve of the modulator. A voltage selection unit selects the direct-current voltage during normal operation, to apply the optical modulator with a bias voltage derived from the direct-current voltage, and selects the bottom voltage at the time of shutdown, to apply the bottom voltage to the modulator.

Optical transmitter device

An optical receiving device which is improved in the accuracy of optical input interruption detection as well as in the alarm response and thus is capable of high-quality detection of interruption of the optical input. A light receiving element receives an optical signal and converts it into an electrical signal. A bias control section stabilizes a bias voltage applied to the light receiving element against variations in temperature and power supply. An optical input interruption protection section protects the light receiving element using a protective voltage so that the light receiving element may not be broken due to an excessive rise of the bias voltage when the optical input is interrupted. An alarm issuing section monitors the photocurrent of the light receiving element and issues an alarm on detecting an interruption of the optical input when the bias voltage and the protective voltage become equal to each other.

Optical receiving device

An APD bias circuit includes an APD, an equalizer amplifier receiving an output signal of the APD, and first, second and third resistors connected in series to the APD to which a bias voltage is applied therethrough. A bias control circuit is connected to a first node between the first and second resistors, and receives a current from the first node so that a voltage of the first node can be maintained at a constant level. A first capacitor is connected between a ground and a second node between the second and third resistors. A second capacitor is connected between the ground and a third node between the third resistor and the APD. A first time constant defined by the second resistor and the first capacitor is greater than a second time constant defined by the third resistor and the second capacitor.

APD bias circuit

An optical communication system transmits an optical signal from an optical sender to an optical receiver. A superimposed signal corresponding to a transmission speed of the optical signal is superimposed on the optical signal. At the optical receiver which receives the transmission light, the transmission speed is detected based on the superimposed signal included in the received light, and setting of a phase-lock loop circuit for extracting a clock signal is switched, to thereby perform a data decision processing of the received light. Thus, it becomes possible to receive and process optical signals at different transmission speeds by a single optical receiver, even when optical signals at the different transmission speeds are transmitted between the optical sender and the optical receiver.

Optical communication system, optical receiver and wavelength converter

Disclosed herein is an optical transmitter suitable for stabilization of the output power and wavelength of an optical signal. The optical transmitter includes a light source for outputting a light beam, an external modulator for modulating the light beam according to a main signal to thereby output an optical signal, a power monitor for detecting the power of the optical signal output from the external modulator, and a control unit for controlling the light source so that the power detected by the power monitor becomes stable. The light source is controlled according to the power detected on the downstream side of the external modulator, so that the output power of the optical signal to be obtained can be maintained constant with high accuracy irrespective of variations in loss by the external modulator.

Optical transmitter

The optical transmission apparatus for multiple wavelengths according to the present invention comprises; a light source, a temperature control section for controlling the temperature of the light source, a temperature control (ATC) loop for controlling the operation of the temperature control section, and a wavelength control (AFC) loop. The ATC loop detects the temperature of the light source and feedback controls the operation of the temperature control section, so that the optical output wavelengths of the light source fall within a wavelength capture range corresponding to a target wavelength of the AFC loop. The AFC loop has a wavelength detection filter having a periodic transmission wavelength characteristic. After the operation of the ATC loop has stabilized, a wavelength capture operation is commenced, and the operation of the temperature control section is controlled so that the optical output wavelength of the light source is captured at a stable point corresponding to a target wavelength, among a plurality of stable points.

Optical transmission apparatus for multiple wavelengths and optical transmission wavelength control method

A WDM optical transmission apparatus of the present invention comprises: a light source ( ) for generating light whose wavelength is changed according to the temperature and a drive current; a temperature control section ( ) for controlling the temperature of the light source so that a wavelength at the starting of emission of the light source is stabilized in an allowable range of optical output wavelength set in advance; a drive current control section ( ) for controlling the drive current applied to the light source according to the allowable range of the optical output wavelength; a wavelength control section ( ) for detecting a wavelength of light output from the light source and controlling the temperature of the light source based on the detection result, to lead the optical output wavelength into the vicinity of a predetermined target wavelength; and an operation control section ( ) for controlling the start and stop of the control operation of each section at predetermined timing respectively corresponding to the time of optical output generation and the time of optical output stop.

WDM optical transmission apparatus

An electronic circuit module has an electronic circuit module main body and two signal pedestals, one on each side of the main body. The first signal pedestal is formed at a level higher than the second signal pedestal by an amount equal to the vertical thickness of the second signal pedestal. Signal lines are formed on a bottom surface of the first signal pedestal and on a top surface of the second signal pedestal. When connected to adjacent electronic circuit modules, the first signal pedestal of the electronic circuit module overlaps a second signal pedestal of one adjacent electronic circuit module, and the second signal pedestal underlaps a first signal pedestal of another adjacent electronic circuit module to electrically connect electronic circuit modules in multiple stages, improving signal connections and reducing the size of the electronic circuit module package.

Electronic circuit module, electronic circuit module connecting structure and connecting member, and method for connecting the same

Disclosed is a laser diode protecting circuit adapted to prevent a laser diode from producing an excessive emission when the laser diode is driven at low temperature, thereby assuring that the laser diode will not be damaged or degraded in terms of its characteristic. When the laser diode is started at low temperature, a laser diode protecting circuit has a power monitor circuit for monitoring backward power of the laser diode and a laser diode current limiting circuit for limiting the laser diode current when the backward power becomes equal to the set power. When the laser diode temperature subsequently rises and the backward power falls below the set power, an automatic current control circuit performs automatic current control in such a manner that the laser diode current attains a set current value. Alternatively, a temperature monitor circuit monitors the temperature of the laser diode and the laser diode current limiting circuit limits the laser diode current when the monitored temperature of the laser diode is less than the set temperature. When the laser diode temperature exceeds the set temperature, the automatic current control circuit performs automatic current control in such a manner that the laser diode attains the set current value.

Laser diode protecting circuit and laser driving current control circuit

Disclosed is a clock extraction circuit for extracting a clock signal which furnishes timing for discriminating a data signal, from the data signal. The clock extraction circuit has a timing extraction unit for extracting the clock signal from the data signal, and a filter, which is provided in front of the timing extraction unit, having an upper limited frequency sufficiently lower than the bit rate of the data. The data signal is input to the timing extraction unit via the filter.

Clock extraction circuit

Laser diode protecting circuit

A clock signal detection circuit includes a diode to which a clock signal is applied as an input. If a voltage VD IN on the anode side of the diode is greater than a voltage VD OUT on the cathode side, the clock signal is fed into a transmission line and arrives at a reflecting load upon elapse of a prescribed delay time. When the voltage VD IN on the anode side of the diode becomes smaller than the voltage VD OUT on the cathode side, the clock signal is reflected by the reflecting load and returns to the cathode of the diode through the transmission line. This introduction and reflection of the clock signal is repeated at the clock signal period so that the amplitude on the output side of the diode is enlarged, thereby making it possible to obtain, from an averaging circuit, a clock detection voltage substantially equal to the amplitude value of the clock signal.

Clock signal detection circuit

A synchronization control unit for synchronizing serial-to-parallel (S/P) converters operating in parallel, or parallel-to-serial (P/S) converters operating in parallel. More specifically, first and serial-to-parallel (S/P) converters produce respectively corresponding first and second clock signals and operate in parallel. The first and second clock signals are in synchronization, and a synchronization failure occurs when the first and second clock signals fall out of synchronization. When a synchronization failure occurs, the synchronization control unit resets one of the first and second clock signals so that synchronization between the first and second clock signals is restored within a definite time period. Moreover, the synchronization control unit can perform the same operation with parallel-to-serial (P/S) converters, instead of with S/P converters.

Synchronization control unit which maintains synchronization between

An optical parallel receiving module receives optical signals transmitted in parallel in a plurality of channels by using optical fibers. The optical parallel receiving module includes photo-electric conversion elements for converting received signals which are electric signals as received signals, limiter amplifiers for comparing the received signals and a threshold level, and data decision circuits for recognizing data at a timing in every period of received data using a reference clock. Each of the data decision circuits includes a data edge position detecting unit for detecting in which region of a plurality of regions a rising edge of the received data is and for outputting a detecting signal corresponding to a detected region, one period of the received data having a reference phase equal to a phase of the reference clock signal being divided into the plurality of regions; and a data acquisition unit to which a plurality of clocks having different phases and the detecting signal from the data edge position detecting unit are supplied, each of the plurality of clocks corresponding to one of the plurality of regions, for acquiring data at a timing of a clock corresponding to the region in which the rising edge of the received data is detected by the data edge position detecting unit.

Data decision circuit used in optical parallel receiving module, optical

A demodulator comprising an OR/NOR circuit, an exclusive OR/NOR circuit, and a delay circuit is disclosed as that capable of being suitably formed into a monolithic IC. Also, a polarization diversity receiver for coherent optical communication using the above demodulator as its constituent is disclosed as that having a smaller number of variable gain amplifiers and accordingly having the controlling circuit made simpler in structure.

Growing community of inventors

Kawasaki, Japan

Tetsuya Kiyonaga