Fujitsu Corporation

Setsuo Misaizu

Motoyoshi Sekiya

Mitsuharu Noda

Tetsuya Kiyonaga

Yasunori Nagakubo

Takashi Tsuda

Hisaya Sakamoto

Nobuaki Sato

Norio Nagase

Kakuji Inoue

Kenichi Kobayashi

Hiroshi Yamada

Makoto Miyoshi

Yuji Miyaki

Sadao Ibukuro

Sunao Itou

Hiroo Kitasagami

Akimitsu Miyazaki

Yasuhiro Tanaka

Keisuke Imai

Tomoyuki Otsuka

Hiroshi Kuzukami

Tetsuji Sato

Isao Nakajima

Masahiko Yamashita

Toru Yamazaki

Hirokazu Osada

Tatsuya Nishimura

Akihiko Yasuda

Kazuhisa Kogure

Shinichiro Sano

Hiroshi Kuwahara

Michinao Kawano

Shihori Imai, Legal Representative

Tomoko Anzai

Takayoshi Ikegami

Yoshinobu Miyamoto

Yuko Yoshida

An identification level control method and an optical receiver are disclosed to determine an optimal identification level in a simple structure without clock extraction. In the identification level control method, an identification level supplied to a limiter amplifier is changed from a lower bound to an upper bound thereof and is stored together with an output average of the limiter amplifier. Then, a first average and a second average are set based on the output average. A first identification level corresponding to the first average and a second identification level corresponding to the second average are obtained, and an optimal identification level is computed based on the first identification level and the second identification level, and is supplied to the limiter amplifier.

Identification level control method and optical receiver

An optical transmitter comprises an amplitude modulation unit performing amplitude modulation of only a one-side amplitude of a main signal with a low-frequency signal having a predetermined frequency. An optical modulator receives an input signal generated after the one-side amplitude modulation, and modulates an incoming light in response to the received signal in accordance with a predetermined modulation-characteristic curve to output an optical output signal. An operating point control unit applies a predetermined bias voltage to the optical modulator to control a level of the input signal substantially applied to the modulation-characteristic curve so that the one-side amplitude of the main signal is applied to a minimum portion of the modulation-characteristic curve of the optical modulator.

Optical transmitter and its control method

There is provided a PLO device which performs high-accuracy, high-quality clock recovery. A shifted data generation part generates shifted data, and a first phase comparison part outputs first difference data. A first filter removes an alternating-current component from the first difference data and outputs a first detection voltage. A delay part delays input data for a time corresponding to half of one time slot with the use of an analog delay element and outputs delayed data. A second phase comparison part compares the phases of the input data and delayed data with each other and outputs second difference data. A second filter removes an alternating-current component from the second difference data and outputs a second detection voltage. An arithmetic section divides the first detection voltage by the second detection voltage to obtain a control voltage. A clock oscillation section outputs recovered clock based on the control voltage.

PLO device

A bias circuit for a photodetector by the present invention provides a bias voltage to the photodetector that performs electric current amplification according to the bias voltage supplied, and is characterized by comprising a power node and an auto-bias circuit that changes a time constant of the bias circuit for the photodetector according to an optical power received by the photodetector, the auto-bias circuit being connected between the power node and the photodetector, thereby reliability of operation of the photodetector is enhanced.

Bias circuit for a photodetector, and an optical receiver

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

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

Laser diode protecting circuit

An optical transmitter comprises a first unit for generating an optical signal having a bandwidth given by a main signal, a second unit modulating the optical signal according to a control signal to extend the bandwidth of the optical signal, a third unit extracting backward light including SBS(stimulated Brillouin scattering) light generated in an optical fiber transmission line, and a fourth unit performing feedback control so that the power of the SBS light becomes substantially constant. Through the structure of the optical transmitter good transmission characteristics of a main signal are obtained and the suppression of the SBS is allowed.

Optical transmitter, optical communication system and optical

An optical transmitter including a light source for outputting a carrier light, an electro-absorption optical modulator for absorbing the carrier light according to an applied voltage to thereby output an intensity-modulated signal light, a device for applying an offset voltage to the optical modulator so that the applied voltage enters a region where the generation of the carrier light in the light source is stable, and a device for receiving an input signal to superimpose a modulation signal corresponding to the input signal on the offset voltage. This optical transmitter prevents wavelength chirping of the light source due to residual reflection in the optical modulator to thereby allow improvement in waveform.

Drive circuit for electro-absorption optical modulator and optical

An optical transmitter includes a laser diode module including a laser diode which outputs a light signal to a transmission line, a driving unit which drives the laser diode in accordance with an input signal indicative of data to be transmitted, and a coupling unit for connecting an output of the driving unit to an input of the laser diode module. The coupling unit allows an alternating current to flow through the laser diode and inhibits the output of the driving unit from being subjected to a direct current from the laser diode module.

Optical transmitter and laser diode module for use in the optical

In an equalizing amplifier that equalizes an electric signal obtained from a light signal received via an optical transmission path, an AGC circuit generates first and second signals from the electric signal by referring to a threshold voltage. The first and second signals are complementary signals. An offset compensation circuit generates a first difference signal based on a difference between the first and second signals, compares the first difference signal with a first reference signal, and outputs, as the threshold voltage, a resultant error signal to the AGC circuit. The threshold voltage is varied so that it is located in the center of an amplitude of the electric signal whereby an offset of the AGC circuit can be compensated for.

Equalizing amplifier, receiver using the same and preamplifier

A light receipt system has a bias circuit and a light-receipt element. The bias circuit controls light input power to the light-receipt element to the optimum multiplication factor. The bias circuit of the light-receipt element has a first resistor, a second resistor, and a third resistor. The first resistor and the second resistor are connected in parallel, and the light-receipt element is connected between a connection of the first resistor and the second resistor, and the third resistor. A bypass current path is provided, connected to a junction point between the first resistor and the second resistor.

Light-receipt system with current bias circuit and pre-amplifier for use

An optical signal transmitter has a laser diode, and an automatic bias current control circuit by which the relation between a light output of the laser diode, a threshold current and bias current are kept constant. The automatic bias current control circuit includes a circuit for modulating a bias current of the laser diode in amplitude with a signal of frequency f1, which is lower than that of the input signal, and a circuit for detecting the signal component of the frequency f1 included in the light output of the laser diode and controlling so as that a detected output becomes a fixed value.

Optical signal transmitter having an apc circuit with automatic bias

An automatic temperature control circuit of a laser diode solves a problem that a temperature control becomes unstable when switching to heat or cool the laser diode. In the circuit, a peltier element changes the temperature of the laser diode by heating or cooling, a temperature detecting section detects the temperature of the laser diode and outputs the corresponding detected voltage, an error amplifying section outputs an error voltage by comparing the detected outputted voltage with a fixed value, a peltier current control section controls the direction of a driving current flowing to the peltier element in correspondence with an error voltage outputted from the error amplifying section. In addition, there is provided a circuit which feed-backs a voltage corresponding to the driving current flowing to the peltier element to an input side of the error amplifying section and adds it to the detected voltage outputted from the temperature detecting section.

Automatic temperature control circuit of laser diode and

Growing community of inventors

Yokohama, Japan

Setsuo Misaizu