Fujitsu Corporation

Other

Kyoto University

Etsuko Hayashi

Yasushi Sugaya

Miki Onaka

Tomoto Tanaka

Masato Nishihara

Shinichirou Muro

Hiroshi Onaka

Norifumi Shukunami

Keiko Sasaki

Susumu Kinoshita

Tomoaki Takeyama

Manabu Watanabe

Hideaki Sugiya

Hisao Nakashima

Hideyuki Miyata

Terumi Chikama

Shinya Inagaki

Ichiro Nakajima

Yoshihito Onoda

Chihiro Ohshima

Shunsuke Ono

Setsuhisa Tanabe

Sinya Inagaki

Manabu Watanbe

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

It is an object of the present invention to provide an optical amplifier using optical amplification mediums each doped with a rare earth element for increasing amplification efficiency of signal light in S-band and the like. To this end, the optical amplifier is constituted such that, when performing optical amplification for S-band and the like in which a center wavelength of a gain peak in the optical amplification medium is located at an outside of a signal band, a gain coefficient of when a pumping condition of the optical amplification medium is maximum is set so that a parameter &#x3b7; obtained by dividing a minimum value of the gain coefficient in the signal band by a maximum value of the gain coefficient outside of the signal band becomes a previously set value or more, wherein, for example, the parameter &#x3b7; can be increased by controlling a temperature of each of a plurality of EDFs between which gain equalizers are disposed.

Optical amplifier

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

The present invention relates to an apparatus for controlling a gain of an optical amplifier, and the apparatus comprises a target gain calculating unit for calculating, as a target gain for an optical amplifier, a value obtained by increasing or decreasing a gain (output) of signal light as the number of wavelengths of wavelength-multiplexed signal light decreases, and a control signal outputting unit for outputting a control signal to the optical amplifier so as to amplify the wavelength-multiplexed signal light with the target gain calculated by the target gain calculating unit. This promptly suppresses a fluctuation of signal light level, particularly, a fluctuation of output light power of an optical amplifier stemming from a variation of the number of wavelengths of wavelength-multiplexed signal light.

Gain control apparatus, optical transmission apparatus, gain control method for optical amplifier, and wavelength multiplex 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

According to an optical surge suppressive type optical amplifier in the present invention, for a WDM optical amplifier having a multi-stages amplification configuration in which a plurality of optical amplifying means is connected in series, an optical amplifying medium capable of causing a homogeneous up-conversion (HUC) phenomenon is applied to the optical amplifying means on the signal light output side, so that an optical surge is suppressed utilizing the degradation of gain efficiency by the HUC caused at the time when the input power is decreased. Further, for a one wave optical amplifier, an optical amplifying medium capable of causing a pair induced quenching (PIQ) phenomenon is applied to the optical amplifying means on the signal light input side, so that the optical surge is suppressed utilizing the degradation of output power efficiency by the PIQ caused at the time when the input power is increased. As a result, it is possible to provide a low cost optical amplifier capable of effectively suppressing the optical surge without leading the complexity of control circuit or optical circuit configuration.

Optical surge suppressive type optical amplifier

An optical fiber includes: a first core portion doped with rare earth ions; a second core portion having a lower refractive index than that of the first core portion, provided along an outer circumference of the first core portion, and doped with the rare earth ions; and a clad portion having a lower refractive index than that of the second core portion and provided along an outer circumference of the second core portion, and is configured such that a concentration of the rare earth ions added to the second core portion is higher than that to the first core portion. With this configuration, it is possible to suppress an amount of FWM crosstalk in an optical amplification by decreasing the length of a fiber while alleviating efficiency deterioration due to concentration quenching.

Optical fiber, manufacturing method of the same, and optical amplifier

A control apparatus comprises a light monitoring unit for dividing a signal wavelength band into at least a band in which output light power of an optical amplifier tends to decrease at an decrease in the number of signal wavelengths and a band including a gain deviation band, and for monitoring inputted light power for the individual divided bands, a calculation unit for obtaining the number of signal wavelengths in the individual divided bands based on a monitor result, and a target gain correction unit for correcting a target gain based on a result of the calculation. This suppresses a transient variation of signal light level due to SHB or SRS at a high speed with a simple configuration without deteriorating noise characteristic, thus enabling optical amplifiers to be further disposed in a multi-stage fashion, which can lengthen the transmission distance of a transmission system including an optical add/drop unit.

Individual band gain equalizer for optical amplifiers

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

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

The present invention has an object to provide a Raman amplifier, a WDM optical communication system and a method of controlling the Raman amplification, capable of optimizing amplification characteristics in response to a change of operating conditions of the system so that transmission quality of the WDM signal light can be maintained in good. In order to achieve the above object, in the Raman amplifier according to the present invention, a plurality of pumping light generated by a pumping light generating section capable of varying a wavelength and power of the plurality of pumping light, are multiplexed by a pumping light multiplexing section that has wavelength variable transmission characteristics, and are supplied to an optical transmission path via a pumping light supplying section, and signal light being propagated through the optical transmission path is Raman amplified, wherein the Raman amplifier comprises a pumping light administrating section that controls supply conditions of the pumping light by adjusting operational setting of the pumping light generating section and the wavelength transmission characteristics of the pumping light multiplexing section in synchronization with the change with time of the system operational conditions.

Raman amplifier and wavelength division multiplexing optical communication system, and method of controlling raman amplification

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.

Multi-wavelength light is inputted to an erbium-doped fiber as an optical amplification medium. Pump light is supplied to this erbium-doped fiber. When a transition from a state signal light on the short wavelength area in the multi-wavelength is input in the erbium-doped fiber to a state the signal light is not input, the output power of signal light on the long wavelength area in the multi-wavelength light can vary. The wavelength of pump light is selected in such a way that the output power of the signal light on the long wavelength area can not be negative when the power varies.

Growing community of inventors

Kawasaki, Japan

Etsuko Hayashi