Fujitsu Corporation

Kyoto University

Shinichirou Muro

Etsuko Hayashi

Tomoaki Takeyama

Yasushi Sugaya

Keiko Sasaki

Masato Nishihara

Miki Onaka

Ichiro Nakajima

Hideaki Sugiya

Yuji Tamura

Yoshio Shimano

Shunsuke Ono

Setsuhisa Tanabe

Ryo Karube

An optical transmission apparatus includes a first transmitter configured to output an optical signal having a wavelength belonging to a first wavelength band, a switch configured to output the optical signal outputted to the first transmitter toward a first transmission line or a second transmission line, a wavelength converter configured to convert the optical signal outputted from the switch toward the first transmission line into an optical signal having a wavelength belonging to a second wavelength band other than the first wavelength band, a second transmitter configured to output an optical signal having a wavelength belonging to the first wavelength band, and a first multiplexer configured to multiplex the optical signal outputted from the first wavelength converter and the optical signal outputted from the second transmitter, and output a multiplexed optical signal to the first transmission line.

Optical transmission system, optical transmission apparatus and transmission method

An amplifying-apparatus that raman-amplifies light transmitted through an optical-fiber-transmission-path, includes: an inputting-unit that inputs pump light to the optical-fiber-transmission-path; a path-switching-unit that is capable of switching between a first state in which the light transmitted through the optical-fiber-transmission-path is output to a first path and a second state in which the light transmitted through the optical-fiber-transmission-path is output to a second path; a splitting-unit that splits the light output to the second path by the path-switching-unit and outputs resulting first light and second light; and a control-circuit that stores information based on a result of reception of the light output to the first path by putting the path-switching-unit into the first state and then controls power of the pump light on a basis of the stored information and a result of reception of the first light output by the splitting-unit by putting the path-switching-unit into the second state.

Raman fiber amplifier and its control via path switching

An optical amplifier includes a first excitation light source that outputs a first excitation light; a second excitation light source that outputs a second excitation light; a first amplifying optical fiber doped with a rare-earth element and excited by the first excitation light to amplify light input to the first amplifying optical fiber; and a second amplifying optical fiber doped with a rare-earth element and excited by the second excitation light to amplify the light from the first amplifying optical fiber. A ratio between the intensity of the first excitation light and the intensity of the second excitation light is controlled according to the number of signal lights wavelength-multiplexed in the light input.

Optical amplifier

An optical amplifier for amplifying light includes a light source for emitting pump light in accordance with current amount; a rare earth element doped optical fiber doped rare earth element, the rare earth element doped optical fiber pumped by the pump light from the light source; a detector for detecting upconversion light leaked from the rare earth element doped optical fiber; a memory for storing correspondence relationship data of the current amount for the light source and an intensity of the upconversion light in normal state of the light source; a difference calculator for calculating a difference between the intensity of the upconversion light being detected by the detector and an amount being obtained by converting the current amount for the light source by the use of the correspondence relationship data; and a discriminator for discriminating whether the difference calculated at the difference calculator exceeds a predetermined value.

In an optical transmission apparatus, levels of signal lights obtained by demultiplexing a WDM signal and corresponding to channels are detected, based on which a channel in which a signal is transmitted and a channel in which no signal is transmitted are determined. An attenuation amount of a channel in which no signal is transmitted in a predetermined range from the channel in which the signal is transmitted is set to a value equal to an attenuation amount of the channel in which the signal is transmitted. An attenuation amount of a channel in which no signal is transmitted out of the predetermined range from the channel in which the signal is transmitted is set to a value larger than the attenuation amount of the channel in which the signal is transmitted. The signal lights are attenuated based on the values and multiplexed.

Optical transmission apparatus and optical attenuation amount control method

An optical amplifier including: a first amplifying unit amplifying an input light by utilizing a first excitation light and thereby outputting a first amplified light; a second amplifying unit amplifying the first amplified light by utilizing a second excitation light and thereby outputting a second amplified light; and a control unit detecting a first absorption rate of the first excitation light and a second absorption rate of the second excitation light, and controlling a level of the first excitation light and a level of second excitation light based on the first absorption rate and the second absorption rate. The first absorption rate corresponds to a ratio of the first excitation light absorbed in the first amplifying unit, and the second absorption rate corresponds to a ratio of the second excitation light absorbed in the second amplifying unit.

A photo-detecting apparatus includes a photodiode that coverts light into electricity, a reverse-voltage switching unit that switches a reverse voltage to be applied to the photodiode, a current-difference detecting unit that detects a change in an output current of the photodiode occurring due to switching of the reverse voltage as a current difference, a correspondence retaining unit that retains a correspondence between the current difference and a dark current, a dark-current calculating unit that calculates a dark current by referring to the correspondence based on the current difference detected by the current-difference detecting unit, and a dark-current correcting unit that corrects the output current of the photodiode based on the dark current to find a photocurrent obtained through photoelectric conversion.

Photo-detecting apparatus and photo-detecting method

A Raman amplifier provided with a pump source outputting a pumping light; a rare-earth doped fiber inputting the pumping light and outputting an excitation light; and a guiding unit guiding the excitation light to an optical fiber to a direction opposite to which a signal light propagates in the optical fiber. Also a Raman amplifier provided with a plurality of pump sources outputting a plurality of pumping lights; a plurality of rare-earth doped fibers inputting the each of the plurality of pumping lights and outputting a plurality of excitation lights; a guiding unit guiding the plurality of excitation lights to an optical fiber to a direction opposite to which a signal light propagates in the optical fiber.

Raman amplifier and excitation light source used thereof

An optical amplifier reducing gain deviation caused by wavelength arrangement has a first-stage optical amplifying unit, an attenuator, a second-stage optical amplifying unit, an automatic gain controller controlling the first- and second-stage optical amplifying units so that a gain of signal light outputted from the second-stage optical amplifying unit to signal light inputted to the first-stage optical amplifying unit is constant, and an attenuation amount controller controlling an attenuation amount at the attenuator to adjust gain-versus-wavelength characteristic at the automatic-gain-controlled first- and second-stage optical amplifying units on the basis of information on wavelength arrangement and an input level of the signal light inputted to the first-stage optical amplifying unit so that gain slope characteristic at the first- and second-stage optical amplifying units due to the wavelength arrangement and the input level is flattened.

Optical transmission system

The present invention relates to an optical transmission apparatus capable of suppressing a transitional gain variation when a number of signal wavelengths changes, and maintaining communication quality in optical signals. The optical transmission apparatus is provided with an optical power control device that varies light power of light for each wavelength component corresponding to a wavelength channel, the light including signal light and spontaneous emission light; a wavelength arrangement information obtaining unit that obtains arrangement information of the wavelength channel of the signal light; and a control unit that controls the power control device based on the arrangement information obtained at the wavelength arrangement information obtaining unit so that light power of a wavelength component of the signal light and light power of a wavelength component other than the wavelength component of the signal light become substantially equal.

Optical transmission apparatus and method of controlling the same

An optical amplifier of the present invention comprises: first and second optical amplifying sections connected in series to each other between an input port and an output port; a first variable optical attenuator arranged on a former stage of the first optical amplifying section; a second variable optical attenuator arranged between the first and second optical amplifying sections; an optical amplification control section that controls the first and second optical amplifying sections; and an optical attenuation control section that controls the first and second variable optical attenuators. The optical amplification control section controls each of the optical amplifying sections so that a gain of the entirety of the optical amplifier is held constant, and the optical attenuation control section controls attenuation amounts of the variable optical attenuators so that monitor values of the output powers from the variable optical attenuators approximate the same value, provided that a value of the sum of the attenuation amounts of the variable optical attenuators decided according to the signal light input power per one wavelength of a WDM light is held constant. As a result, it becomes possible to provide at a low cost the optical amplifier capable of achieving flat output wavelength characteristics and the favorable NF, irrespective of the signal light input power per one wavelength of the WDM light and the number of wavelengths thereof.

In an optical transmission apparatus, optical power of each of wavelength contained in a wavelength multiplexing signal is measured, a measured value of the optical power of each wavelength is compared with a predetermined threshold value, a total value of the measured values of the optical power, which are equal to or larger than the threshold value, is calculated as a total value of signal beam power, and a total value of the measured values of the optical power, which are less then the threshold value, is calculated as a total value of ASE power. The number of the measured values of the optical power, which are equal to or larger than the threshold value, is calculated as a wavelength count of the signal beams contained in the wavelength multiplexing signal. A signal-to-ASE ratio is calculated from the total value of the signal beam power and the total value of the ASE power. The optical power of the wavelength multiplexing signal inputted to an optical amplifier is measured, and a target value of the automatic level control (ALC) is determined by use of the measured values of the wavelength count, the signal-to-ASE ratio and the optical power of the wavelength multiplexing signal in order to execute the ALC of the optical amplifier so that the optical power of each of the wavelengths in the wavelength multiplexing signal outputted from the optical amplifier, becomes constant.

Optical transmission apparatus

In an optical amplification characteristics simulation apparatus according to the present invention, using spectrums of a signal light input to an optical amplifier and a characteristic parameter for amplification medium, gain wavelength characteristics of the amplification medium are calculated. A calculating formula for the above has a parameter corresponding to a gain fluctuation portion due to a gain spectral hole burning (GSHB) phenomenon, and this parameter is defined by a function obtained by modeling a physical phenomenon in which a population inversion rate is reduced due to the GSHB, based on that electron occupation numbers in each Stark level on the end level side are increased. Then, based on the calculated gain wavelength characteristics, the output power of the signal light is obtained, to thereby perform the optical amplification characteristics simulation on the optical amplifier. As a result, it is possible to construct a high versatile calculation model based on the physical phenomenon for the gain fluctuation due to the GSHB, to thereby simulate with high precision the optical amplification characteristics of the optical amplifier under arbitrary conditions.

Optical amplification characteristics simulation apparatus and optical amplification characteristics simulation method

In an optical transmission system according to one aspect of the present invention, for transmitting a WDM light from a transmission station to a reception station, utilizing a Raman amplifier, the Raman amplifier comprises an optical amplification medium; a pumping light source generating a plurality of pumping lights having wavelengths different from each other; an optical device introducing the plurality of pumping lights to the optical amplification medium; and control means for controlling the pumping light source, the transmission station sends out a plurality of reference lights having wavelengths at which respective Raman gain obtained by the plurality of pumping lights reach peaks or wavelengths close to the above wavelengths, and the control means controls the plurality of pumping lights based on the optical powers of the plurality of reference lights. Thus, it becomes possible to accurately manage the optical power balance of the WDM light and the optical power of the entire WDM light.

Optical amplifier provided with control function of pumping light, and optical transmission system using the same

There is provided an optical amplifier including a Raman amplification medium, a rare earth doped fiber located at a latter stage of the Raman amplification medium, a first pump light outputting unit for outputting pump light with a plurality of wavelengths, a variable distribution element for distributing the pump light with the plurality of wavelengths, outputted from the first pump light outputting unit, to the Raman amplification medium and the rare earth doped fiber in a variable distribution ratio for each wavelength, and a control unit for individually controlling the distribution ratio of the pump light with the plurality of wavelengths in the variable distribution element and the power of the pump light with the plurality of wavelengths from the first pump light outputting unit in accordance with a wavelength arrangement of each of signal lights wavelength-multiplexed into the wavelength-multiplexed signal light.

Growing community of inventors

Kawasaki, Japan

Shinichirou Muro