Fujitsu Corporation

Naomasa Shimojoh

Takao Naito

Takafumi Terahara

Terumi Chikama

Toshiki Tanaka

Hiroshi Nakamoto

The present invention has an object to provide an optical transmission technology using Raman amplification wherein a supervisory signal transferred among a plurality of optical transmission apparatuses is superimposed on a main signal light by using a pumping light for Raman amplification. To this end, a Raman amplifier applied with the optical transmission method of the present invention, is provided with a supervisory signal superimposing section for superimposing a supervisory signal transferred among the optical transmission apparatuses on at least one of a plurality of pumping lights of different wavelengths to be supplied to a Raman amplification medium via a multiplexer from a pumping light generating section, thereby transmitting the main signal light propagated through the Raman amplification medium to be Raman amplified, which is superimposed with the supervisory signal.

Optical transmission method and optical transmission system utilizing Raman amplification

An optical amplifier is provided for performing amplification of optical signals of two wavelength bands, where deterioration in the optical SN ratio relative to one wavelength band is reduced, with a simple construction which can deal with restrictions on installation space, power consumption and the like. To this end, the present optical amplifier has a C/L band optical amplifying section for amplifying respective optical signals of a C band and an L band, a demultiplexer for demultiplexing output light from the C/L band optical amplifying section into the C band and the L band, an L band optical amplifying section for amplifying L band optical signals which have been demultiplexed by the demultiplexer, and a multiplexer for multiplexing the C band optical signals which have been demultiplexed by the demultiplexer and the L band optical signals which have been amplified by the L band optical amplifying section. The construction is such that a part of excitation light of a 1480 nm band used in the C/L band optical amplifying section is supplied via an input terminal to a Raman amplification producing medium of a transmission path, and Raman amplified L band optical signals are input to the C/L band optical amplifying section.

Optical amplifier

A gain equalizer which equalizes gain versus wavelength characteristics of an optical amplifier. The gain versus wavelength characteristics of the optical amplifier include first, second and third gain peaks in a wavelength band with the second gain peak being between the first and third gain peaks. The optical amplifier amplifies an input signal in accordance with the gain versus wavelength characteristics to produce an output signal. The gain equalizer includes first, second and third optical filters having first, second and third transparency characteristics, respectively. The first, second and third transparency characteristics are periodic waveforms having different periods related to the wavelength difference between the first and third gain peaks. The second transparency characteristic is a periodic waveform having a period equal to 1/(2 ) of the period of the waveform of the first transparency characteristic. The third transparency characteristic is a periodic waveform having a period equal to &frac14; of the period of the waveform of the first transparency characteristic. For example, the first transparency characteristic is a periodic waveform with &frac14; period extending between the first and third gain peaks, the second transparency characteristic is a periodic waveform with one period extending between the first and third gain peaks, and the third transparency characteristic is a periodic waveform with two periods extending between the first and third gain peaks.

Gain equalizer which includes a plurality of optical filters for equalizing the gain of an optical amplifier

The present invention is aimed at providing an optical repeater using Raman amplification that can Raman amplify WDM signal lights propagated through a plurality of transmission systems, with high excitation efficiency and stability. To this end, an optical repeater using Raman amplification of the present invention multiplexes and demultiplexes excitation lights supplied from a plurality of excitation light sources in a star coupler and then supplies the resultant demultiplexed lights to Raman amplification media of a plurality of transmission systems via optical multiplexers, to thereby Raman amplify the WDM signal lights of the respective transmission systems. Moreover, by feedback controlling the power of each excitation light based on the result of monitoring the WDM signal light power after Raman amplification in each transmission system, a stabilized Raman amplification operation with reduced dispersion in the power of each excitation light output from the star coupler is realized.

Optical repeater using raman amplification, wavelength division multiplexed light transmission system, excitation light supply method and excitation light control method for raman amplification

An object of the invention is to provide, for an optical amplifier which performs amplification of optical signals of two wavelength bands, an optical amplifier and an optical amplification method of a simple configuration which can deal with restrictions on installation space, power consumption and the like. Hence with the optical amplifier of the invention, optical circulators are respectively connected to opposite ends of an optical amplifying means, and optical signals of the respective wavelength bands of a first wavelength band and a second wavelength band are input and output to the optical amplifying means via each of the optical circulators so that the propagation directions of the respective optical signals of the respective wavelength bands are in mutually opposite directions inside a rare earth element doped fiber. As a result, the optical signals of the respective wavelength bands can be collectively amplified with a simple configuration using a single rare earth element doped fiber.

Optical amplifier and optical amplification method for amplifying wavelength division multiplexed signal light

A device for equalizing the gain-wavelength characteristics of an optical repeater used in a long distance optical transmission system, wherein the gain-wavelength characteristics are equalized by one optical filter having asymmetrical loss-wavelength characteristics in a desired wavelength range order to flatten the gain-wavelength characteristics curve over a wide wavelength range. Since such a device can equalize the gain by one optical filter, adjustment the would normally be required between plural optical filters is unnecessary, so that it is simple and cost effective.

Method of equalizing gain utilizing asymmetrical loss-wavelength characteristics and optical amplifying apparatus using same

An object is to provide a low cost optical amplifier having a simple construction where gain equalization of wavelength division multiplexed signal light, and the suppression of noise light is realized by a single optical device, and to provide a wavelength division multiplexed light transmission system using such an amplifier. Accordingly, the optical amplifier of the present invention is constructed by providing for a conventional optical amplifier incorporating an EDF, an excitation light source and a multiplexer, an optical filter having a periodic loss-wavelength characteristic with respect to a gain wavelength characteristic of the EDF. The optical filter has the characteristic that a spacing (FSR) corresponding to one period of a loss-wavelength characteristic corresponds to a gain peak wavelength difference of the EDF, and a maximum loss wavelength approximately coincides with a gain peak wavelength on a long wavelength side of the EDF. With such an optical filter, gain equalization of the signal light positioned in the gain peak wavelength neighborhood on the long wavelength side can be effected, and noise light generated in the gain peak wavelength neighborhood on the short wavelength side can be suppressed.

Optical amplifier and wave length division multiplexed light transmission system

The present invention aims at providing an active optical fiber and an optical fiber amplifier, in which a conversion efficiency of pumping light to be input into the active optical fiber is increased to thereby improve optical amplification characteristic. To this end, the active optical fiber of the present invention is formed with fiber gratings arranged over a predetermined region along the longitudinal direction within the optical fiber doped with a rare earth element, and transmitting signal light and reflecting pumping light. Further, the optical fiber amplifier of the present invention is constituted to comprise a pumping light source for generating pumping light, and a multiplexer for multiplexing signal light and the pumping light to thereby output them into one end of the active optical fiber. Thus, the pumping light is reflected by the fiber gratings so as to go and return within the active optical fiber, thereby improving the conversion efficiency of the pumping light.

Growing community of inventors

Kawasaki, Japan

Naomasa Shimojoh