Nec Corporation

Mitsubishi Cable Industries, Ltd.

Hideki Okuno

Atsushi Toyohara

Minoru Yoshida

Kazuo Imamura

Katsuaki Kondo

Takashi Okuyama

Yasuhide Sudo

Tatsuhiro Kawamura

Yoshiyuki Imada

An optical transmission system includes an optical signal transmitter to output optical signal, a monitoring light transmitter to generate monitoring light, an optical multiplexer to output a multiplexed signal light by multiplexing the optical signal and monitoring light, an optical relay transmission path to amplify the multiplexed signal light by using a Raman amplification effect, an optical demultiplexer to demultiplex the multiplexed signal light, a monitoring light receiver to receive the monitoring light output from the optical demultiplexer, and a pumping light source stopping device to continuously monitor a transmission state of the monitoring light and, when the transmission of the monitoring light is interrupted, to stop emission of the pumping light from the pumping light source to be used for distributed Raman amplification.

Optical transmission system, and pumping light source stopping device and method to be used in same system

The present invention includes a sheet material, a first optical fiber, a second optical fiber optically coupled to the first optical fiber in portions thereof, and an optical fiber coupler constituted in the portions where the two optical fibers are coupled, and those of the first and second optical fibers, and the optical fiber coupler are integrally held in the sheet material.

Optical fiber holding structure

An optical fiber amplifying apparatus is provided with an optical fiber for amplifying input signal lights, a heating/cooling element for heating or cooling the optical fiber, and a temperature control circuit for controlling the element. The circuit effects control so as to keep the optical fiber at a prescribed temperature on the basis of the output of a temperature sensor. The circuit also controls the heating/cooling element so as to keep the level(s) of at least one signal light extracted out of wavelength-multiplex signal lights at a prescribed value. The circuit can compute the gain from the input and output levels of one or more signal lights, and control the element so as to keep this gain within a prescribed range.

Optical fiber amplifying device stabilized for temperature and signal level

Disclosed is a method for wavelength-multiplexing signal lights with three or more wavelengths, wherein: a wavelength arrangement is made by providing at least a wavelength block of signal light with one wavelength and a wavelength block where signal lights with two or more wavelengths are wavelength-multiplexed or providing a plurality of wavelength blocks where signal lights with two or more wavelengths are wavelength-multiplexed, and by setting a wavelength interval between adjacent wavelength blocks to be wider than a wavelength interval between signal lights in a wavelength block.

Wavelength division multiplexing system, wavelength division multiplexing transmission system and optical path cross connection system

An optically amplifying device with a gain equalizing function comprises: an optical fiber amplifier for receiving, as an input, a wavelength division multiplexed signal light beam which has been obtained by wavelength-division multiplexing a plurality of signal light beams having different wavelengths to output the amplified signal light beam containing the plurality of signal light beams, which is obtained by optically amplifying the wavelength division multiplexed signal light beam; and a gain equalizer for receiving, as an input, the amplified signal light beam to optically amplify the plurality of signal light beams thus amplified to equalize the optical output levels thereof, thereby outputting the equalized amplified signal light beams. The gain equalizer includes a semiconductor optical amplifier, the gain for each of the plurality of signal light beams of the semiconductor optical amplifier is set in a way that when the gain for each of the plurality of signal light beams of the semiconductor optical amplifier is superimposed on the gain for each of the plurality of signal light beams of the optical fiber amplifier, the gain difference between the signal light beam is cancelled out. The gain equalizer may be disposed either before the optical fiber amplifier or between the two optical fiber amplifiers. In the optical amplification of the wavelength division multiplexed signal light beam containing the plurality of signal light beams having different wavelengths, the optical output difference occurring between the levels of the amplified signal light beams is reduced effectively.

Optically amplifying device with gain equalizing function

Disclosed is an optical amplification device comprising a pulser for pulsing a multi-channel signal which has been wavelength division multiplexed; a pulse signal disperser for dispersing the pulsed signal at each wavelength and outputting a dispersed pulse signal; and an optoelectronic converter for converting the dispersed pulse signal to an electrical signal. The number of channels of a multi-channel signal can be counted by counting the number of peaks in a time waveform of the electrical signal. The pulse signal disperser can be realized by using a high dispersion medium having high wavelength dispersion. The pulser can be realized by using an optical switch utilizing a mechanical, acousto-optical or electro-optical effects. The optical signal channel counter can be applied in an optical amplification device and stable optical amplification can be performed by counting the number of channels of an inputted optical signal and outputting pump light in compliance with said number of channels. The number of channels of a multi-channel signal can thus be counted accurately and the configuration of the counter which executes counting can be simplified.

Optical signal channel counter and optical amplification device using

In an optical amplification monitoring apparatus of the invention, the number of signal light beams actually being transmitted is detected and an optical amplifier is controlled in accordance with the detected number. There is provided a means for monitoring intermodulation light beams resulting from signal light beams of two wavelengths which means includes a nonlinear medium and a WDM coupler that are provided on a light transmission path, an optical fiber grating for allowing passage of only intermodulation light components among the branched light beams, and a photodetector for converting the detected intermodulation light components into currents. A dispersion-shift optical fiber having a zero-dispersion wavelength in the 1.55-.mu.m band is used as the nonlinear medium. Intermodulation light beams are generated only when both signal light beams having different wavelengths w1 and w2 exist in the nonlinear medium. Since the intermodulation light beams have different wavelengths than the signal light beams, the number of signal light beams can be detected by monitoring the intermodulation light beams separated from the signal light beams. Thus, in wavelength-multiplexed transmission, optical amplification can be performed independently of the number of signal light beams actually being transmitted.

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Tokyo, Japan

Hideki Okuno