Fujitsu Corporation

Yokogawa Electric Corporation

Hitachi Cable, Inc.

Fujitsu Network Communications, Inc.

Hirota, Osamu

Hiroshi Onaka

Hideyuki Miyata

Kazue Otsuka

Motoyoshi Sekiya

George Ishikawa

Terumi Chikama

Yutaka Kai

Nobuhiro Fukushima

Takeshi Hoshida

Tadao Nakazawa

Susumu Kinoshita

Takao Naito

Kazue Okazaki

Yasushi Sugaya

Hiroki Ooi

Takafumi Terahara

Setsuo Yoshida

Hiroaki Tomofuji

Miki Onaka

Akira Miura

Etsuko Hayashi

Naoki Hashimoto

Shigeki Watanabe

Kentaro Nakamura

Toru Katagiri

Jens Rasmussen

Tetsuya Kiyonaga

Yoshihito Onoda

Hiroshi Miyata

Osamu Hirota

Yoichi Takasu

Yasuyuki Suzuki

Yuichi Akiyama

Goji Nakagawa

Shinya Inagaki

Hiroyuki Matsuura

Kazuo Yamane

Kazumasa Takabayashi

Kyosuke Sone

Martin Bouda

Takeshi Sakamoto

Morio Wada

Hiroshi Nakamoto

Kazuo Hironishi

Minoru Seino

Ken Morito

Keiko Takeda

Akihiko Isomura

Miki Takeda

Hideaki Arai

Tomohiro Ueno

Yoshihiro Saito

Kaoru Moriya

Makoto Murakami

Kazumasa Kubotera

Yuji Kotaki

Hideo Kuwahara

Satoshi Takasugi

Yoshihto Onoda

Jens C Rasmussen

Martin c/o Fujitsu Limited Bouda

An apparatus comprising an optical modulator modulating a light in accordance with a modulation signal and an operating point of the optical modulator, to thereby output a modulated optical signal; and a controller controlling the operating point in accordance with a branched portion of the modulated optical signal and a detected intensity of the modulation signal so that the operating point is kept stable when the detected intensity falls below a predetermined value.

Optical communication apparatus and optical add/drop apparatus

An optical transmission apparatus for suppressing deterioration of transmission quality due to XPM in a wavelength division multiplexing optical communication system in which an intensity modulation optical signal and a phase modulation optical signal exist in a mixed form. The apparatus has an intensity inversion signal light output section which outputs light having an intensity pattern obtained by inverting intensity changes of the intensity modulation optical signal near a wavelength of the intensity modulation optical signal in arrangement on wavelength axis of optical wavelengths that can be multiplexed as a wavelength division multiplexed signal as intensity inversion signal light, and a wavelength division multiplexed optical signal output unit which wavelength-division-multiplexes the intensity modulation optical signal, the phase modulation optical signal and light from the intensity inversion signal light output section and outputs a wavelength division multiplexed optical signal.

Optical transmission apparatus, wavelength division multiplexing optical communication system and optical transmission method

A variable dispersion compensating unit compensates an optical signal, and changes the compensation amount according to a control signal that has a given frequency. After demodulation of the compensated optical signal, error conditions of the signal are monitored and an error signal is output. A band pass filter filters the error signal for a component having a frequency equal to or less than the given frequency. Based on the component and on the control signal, a synchronous detecting circuit generates a compensation amount modification signal. The compensation amount modification signal is superposed on the control signal.

Dispersion compensating apparatus and dispersion compensation control method

An interferometer for demodulating a differential M-phase shift keying signal includes a PLC type interferometer main body, a heating portion that heats the PLC type interferometer main body, and an intermediate member having a higher stiffness than that of the PLC type interferometer main body, for bonding the PLC type interferometer main body and the heating portion with each other while being sandwiched therebetween. A linear expansion coefficient difference between the PLC type interferometer main body and the intermediate member is equal to or smaller than 4.5&#xd7;10/&#xb0; C., and a thermal conductivity difference between the PLC type interferometer main body and the intermediate member is equal to or larger than 10 W/mK. A phase of an optical signal flowing through the interferometer is adjusted by using the heating portion and a second heating portion.

Interferometer for demodulating differential M-phase shift keying signal

A data modulator unit generates a DQPSK optical signal in accordance with a data signal. A phase shift unit provides a phase difference of &#x3c0;/2 between a pair of arms. A photodetector converts an output signal of the data modulator unit into an electrical signal. A filter is a low-pass filter with a cut-off frequency lower than a symbol frequency, and filters an output signal of the photodetector. A monitor unit detects power of an output signal of the filter. A phase difference control unit adjusts the amount of phase shift in the phase shift unit so as to minimize power of an output signal of the filter.

Optical transmitting apparatus and optical communication system

An encryption technique allowing use of classic Y-00 scheme performed using classic physical random numbers instead of quantum fluctuation in electrical communication and data storage in recording media, including a first modulation step for multilevel-modulating input data by associating with specific state pairs determined by physical random numbers, a second modulation step for outputting the output of the first step by irregularly associating with another signal by physical random numbers, and a channel coding step for channel-coding the output of the second step into desired codeword and outputting it as encrypted data, wherein the decoded signal obtained by channel-decoding the encrypted data can be discriminated which of specific state pairs the signal corresponds to and demodulated into the input data, and output by the first modulation by state pairs other than the specific state pairs and the second modulation by a physical random number different from the physical random number.

Encryption method, cryptogram decoding method, encryptor, cryptogram decoder, transmission/reception system, and communication system

A chromatic dispersion monitoring apparatus according to the present invention comprises: a photodetector which photo-electrically converts an optical signal; a low-pass filter which limits a frequency bandwidth of the photo-electrically converted electrical signal to be within a range set according to a modulation format of the optical signal and a bit rate thereof; a DC elimination circuit which eliminates a direct current component of the bandwidth limited electrical signal; and a power detector which detects the power of the bandwidth limited electrical signal to detect the residual dispersion of the optical signal. As a result, it becomes possible to easily realize the chromatic dispersion monitoring apparatus of low cost, which is also capable to be arranged on an in-line.

Chromatic dispersion monitoring method and chromatic dispersion monitoring apparatus, and optical transmission system

An optical amplifier of the present invention comprises: an optical amplifying circuit which amplifies a signal light; an optical reflection medium which is disposed on an optical fiber connected to the optical amplifying circuit and is capable of reflecting a noise light which exists in a predetermined wavelength range outside a signal band, among noise lights generated in said optical amplifying circuit, to radiate the reflected noise light to the outside of a core of the optical fiber; a light receiver which receives the noise light reflected to be radiated to the outside of the core of the optical fiber by the optical reflection medium, to detect the power of the noise light; and a computation circuit which computes the total power of the noise lights generated in the optical amplifying circuit based on the detection result of the light receiver. Thus, it is possible to provide at a low cost an optical amplifier provided with a monitoring function capable of detecting high accurately, with a simple optical circuit configuration, the noise light power and the like generated when the signal light is amplified.

Optical amplifier and optical monitor circuit

The present invention is an optical waveform shaper that utilizes a plurality of interferometers. Each interferometer has one of two types of transfer functions. One type is a first transfer function characterized as having a positive second order derivative of the output optical power in respect to the input optical power. Another type is a second transfer function characterized as having a negative second order derivative of the output optical power in respect to the input optical power. The characteristics of both the first transfer function and the second transfer function are actualized when the input optical power is in the neighborhood of zero and the output optical power shows substantially periodic change with respect to the input optical power. At least one of the plurality of interferometers uses the second transfer function.

Optical waveform shaper

An optical receiver comprises branching units for branching and supplying the signal lights to be inputted to the first to fourth optical waveguides provided on a substrate, second to third optical waveguides for giving delay time differences corresponding to a symbol of the DMPSK modulated signal, a demodulating unit for demodulating two light signals through interference of signal lights between the first to second optical waveguides and between the third to fourth optical waveguides, two optical detectors for converting two light signals from the demodulating unit, and a light path length varying unit for identically varying each light path length of two optical waveguides being arranged through selection of combinations of the first and third optical waveguides, the first and fourth optical waveguides, and the second and third optical waveguides in one region when the wavelength of the signal light is varied.

Optical receiver and optical receiving method corresponding to differential M-phase shift keying system

A method and system for transmitting information in an optical communication system includes modulating a non-intensity characteristic of an optical carrier signal with a data signal to generate an optical information signal. The optical information signal is transmitted over an optical link. The optical information signal is amplified over a length of the optical link with a co-launched amplification signal traveling in the optical link in a same direction as the optical information signal.

Method and system for transmitting information in an optical communication system using distributed amplification

An encryption technique having a greater encryption strength than conventional mathematical encryption by using classic physical random numbers etc., including a step for modulating one-bit input data into a coded signal by associating it with a discrete value of at least two bits determined by pseudo random numbers and physical random numbers and a step for channel-coding and outputting the coded signal, wherein 1) the coded signal can be demodulated into the input data by the pseudo random number, 2) the number of sets of input data, pseudo random number, and physical random number corresponding to a particular discrete value is equal for two values of the input data, and 3) the number of sets of pseudo random number and physical random number corresponding to respective values of the input data and respective values of the discrete value is equally associated also with any set of them.

Encryption method, cryptogram decoding method, encryptor, cryptogram decoder, and communication system

Disclosed herein is an optical node device applicable to an optical network including a closed loop provided by an optical fiber. This optical node device includes a tunable wavelength selecting element adapted to input WDM signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths, the tunable wavelength selecting element having a function of dropping at least one optical signal from the WDM signal light and a function of adding at least one optical signal to at least one unassigned wavelength channel of the WDM signal light; and a wavelength selecting filter optically connected to the tunable wavelength selecting element for removing noise present in any bands other than a signal band of each optical signal passing through the tunable wavelength selecting element. With this configuration, the oscillation of optical power in the closed loop can be prevented by the use of the wavelength selecting filter for removing noise in any bands other than the signal band.

Optical node device and system including the device

Growing community of inventors

Kawasaki, Japan

Hiroshi Onaka