Fujitsu Corporation

Yuji Tamura

Hiroyuki Itou

Michikazu Shima

Kazuo Yamane

Tsukasa Takahashi

Yumiko Kawasaki

Kazuhiro Suzuki

Shigeki Watanabe

Norifumi Shukunami

Kosuke Komaki

Toshihiro Ohtani

Takashi Tsuda

Shinichirou Muro

Hideaki Sugiya

Kenichi Sasaki

Tatsuya Tsuzuki

Yasunori Nagakubo

Tomoto Tanaka

Yoshihito Onoda

Masao Nakata

Yoshio Shimano

Takashi Satou

Yuji Miyaki

Yoshinori Ohkuma

Keisuke Imai

Tomoyuki Otsuka

Mikinori Yamanaka

An optical transmission system includes an optical transmission apparatus and an optical receiving apparatus. The optical transmission apparatus includes a transmitting unit that transmits signal light to the optical receiving apparatus through an optical transmission path, and a determining unit that determines continuity of the optical path using return light that returns from the optical receiving apparatus to the optical transmission apparatus through the optical transmission path, out of the signal light. The optical transmission apparatus includes a modulating unit that modulates a part of the signal light that is transmitted from the optical transmission apparatus through the optical transmission path to generate the return light, and an output unit that outputs the return light to the optical transmission apparatus through the optical transmission path.

Optical transmission system and optical receiving apparatus

An optical amplifying device includes a semiconductor laser that outputs a pump light having a power according to a provided drive current; a rare-earth-doped amplifying medium that amplifies an input light by the pump light output from the semiconductor laser; and a detector that detects, in the power of the pump light, a fluctuation faster than a response speed of a gain of the amplifying medium with respect to the power of the pump light. The optical amplifying device varies the drive current provided to the semiconductor laser based on the fluctuation detected by the detector.

Optical amplifying device and optical amplifying method

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.

Optical amplifier

According to an aspect of the embodiment of the invention, an optical amplifier including an input port, an output port, a plurality of amplifying parts, an optical attenuator, a gain controller and an optical attenuator controller. The plurality of amplifying parts includes an optical amplification medium and a pumping light source for generating pump light. The optical attenuator is optically connected between the amplifying parts. The gain controller controls the pump light power of the pump sources, respectively, in such a way that the ratio decreases in accordance with the gain set value increasing and the ratio interpose between a first threshold level and a second threshold level. The optical attenuator controller controls attenuation of the optical attenuator in order to maintain the sum of generating gains of the amplifying parts in the gain set value in accordance with a state of the signal light inputted into the input port.

Multistage optical amplifier with gain control using pump ratio

A controller monitors output level variation rate of excitation light outputted by a light source in accordance with a drive current of the light source and provided to a rare-earth doped amplifying medium so that a signal light is amplified as the signal light travels through the amplifying medium. In an embodiment, the controller decreases the drive current when the monitored output level variation rate is larger than a threshold value, to thereby reduce power level of the outputted excitation light and thereby delay progress of degradation of the light source indicated by the monitored output level variation rate being larger than the threshold value.

Control of a light source providing excitation light

An optical amplifier includes a first optical amplification unit that amplifies input light, a variable optical attenuation unit that attenuates an output of the first optical amplification unit, a second optical amplification unit that amplifies an output of the variable optical attenuation unit, and a loss amount control unit that controls the variable optical attenuation unit, wherein an external attenuating optical medium is inserted between the variable optical attenuation unit and the second optical amplification unit. The optical amplifier includes an abnormality detecting unit that detects abnormality in optical loss based on a light level between the external attenuating optical medium and the second optical amplification unit, and a detection invalidating unit that invalidates any abnormality detected by the abnormality detecting unit when a light level between the variable optical attenuation unit and the external attenuating optical medium is lower than a threshold level.

Optical amplifier and abnormality detection method for the same

In an optical switch device, an optical control pulse is inputted into a nonlinear optical fiber in phase with each optical pulse of signal light which is to be outputted, so that the polarization directions of the optical control pulse and the signal light form a predetermined angle at the input stage of the nonlinear optical fiber, the optical control pulse causes polarization rotation and parametric amplification of the optical pulse in the nonlinear optical fiber, and then the optical pulse is outputted through a polarizer. The excitation level of the optical control pulse is set on the basis of the difference of a monitored output level of the optical pulse from a target level so that the output levels of optical pulses of the signal light are controlled at one or more desired levels.

Optical switch device and optical switching method

A light amplification control unit whereby the gain of an optical amplifier can be controlled with ease. A plurality of pump light sources each generate a pump beam having the effect of amplifying a signal beam, and an external control light source generates an external control beam having a wavelength that influences the signal beam amplification effect by means of the pump beams. A multiplexing section multiplexes the pump beams with the external control beam and causes the multiplexed beams to enter an optical fiber in a direction opposite to that of the signal beam. A control section controls the output of the external control beam from the external control light source, whereby the gain of the signal beam amplified by the pump light sources can be controlled.

Light amplification control unit and method

In an optical amplifier of the present invention, a part of an input light output from a transmission path fiber is branched as a monitor light, a frequency component corresponding to a period at which a header area of a framed signal light appears, is extracted, and when a voltage level of a direct-current signal obtained by direct-current converting the frequency component becomes lower than a reference voltage, the input interruption of the signal light is detected, to perform a shut-down control of a pumping light source. Thus, an optical amplifier of low cost capable of suppressing an influence of a noise light while ensuring the immediacy, is provided.

Signal light interruption detecting method and optical amplifier using same

A constant current driving circuit for supplying a constant current to a load circuit includes: a first driver circuit having a pulse width converting circuit for converting a first difference detection signal into a pulse signal having a pulse width corresponding to a signal level of the first difference detection signal, a switch turned on/off on a basis of the pulse signal, and a smoothing circuit for supplying a smoothed first load current to the load circuit; a first current detecting circuit for converting the first load current into a first voltage corresponding to the first load current, and outputting a first current detection signal; a second driver circuit for supplying a second load current to the load circuit on a basis of a signal level of a second difference detection signal; a second current detecting circuit for converting the second load current into a second voltage corresponding to the second load current, and outputting a second current detection signal; a first difference detecting circuit for calculating the first difference detection signal to make zero a difference between the first current detection signal and an input voltage; a second difference detecting circuit for detecting a difference voltage between the first current detection signal and the input voltage, and outputting a third difference detection signal; and a third difference detecting circuit for detecting a difference voltage between the third difference detection signal and the second current detection signal, and outputting the second difference detection signal.

Constant current driving circuit

An optical amplifying apparatus, an optical output controlling method by the optical amplifying apparatus and an optical transmitting apparatus, in which an optical output constant control is possible irrespective of an optical input level even when power-on is detected or an optical signal inputted after supply of pump light is stopped is recovered. The optical amplifying apparatus has an pump light outputting unit, an optical amplifier amplifying an input optical signal with pump light from the pump light outputting unit, an output constant control unit controlling the pump light outputting unit to keep a level of the amplified optical signal constant, an optical input monitoring unit, a pump light level setting unit setting an optical level of the pump light based on a result of optical input monitoring from the optical input monitoring unit, a pump light monitor control unit monitoring a level of the pump light to control the pump light outputting unit so as to stabilize an output level of the pump light at an optical level set by the pump light level setting unit, an input disconnection detecting unit, and an operation control switching unit switching a control mode for pump light to an output constant control mode, a pump light control mode or a stop control mode.

Optical amplifying apparatus, an optical output controlling method by the optical amplifying apparatus, and an optical transmitting apparatus

The invention relates to an optical amplifier; more particularly, the invention provides an optical amplifier that contains a front-end optical amplifier and a back-end optical amplifier, and that is equipped with an automatic compensation function for automatically detecting and compensating for signal loss caused by a dispersion compensator inserted between the front-end and back-end optical amplifiers. The optical amplifier, which contains a front-end optical amplifier,and a back-end optical amplifier,comprises: a loss detection means,for detecting optical signal loss occurring between the front-end optical amplifier and the back-end optical amplifier; and a gain control means,for compensating, based on the loss detected by the loss detection means, for a variation in optical output power of the entire optical amplifier including the front-end optical amplifier and back-end optical amplifier.

An optical power monitor for an optical signal having a signal spectrum superimposed on a noise spectrum. Typically, the optical power monitor includes an optical coupler, first and second optical band-pass filters, first and second photodetectors, and an operating unit. The optical coupler branches the optical signal into first and second beams. The first optical band-pass filter has a first pass band including the signal spectrum, and the first beam is supplied to the first optical band-pass filter. The second optical band-pass filter has a second pass band including the signal spectrum and narrower than the first pass band, and the second beam is supplied to the second optical band-pass filter. The first photodetector receives the first beam passed through the first optical band-pass filter, and the second photodetector receives the second beam passed through the second optical band-pass filter. The operating unit calculates the power of the optical signal according to output signals from the first and second photodetectors. Since the first and second optical band-pass filters have different pass bands, the power of the optical signal relating to the signal spectrum can be precisely monitored with no effects of the noise spectrum.

Optical power monitor and optical amplifier having the optical power

Spontaneous emission occurring in association with direct optical amplification using an erbium-doped optical fiber is modulated with an auxiliary signal, such as a supervisory signal, for transmission of the auxiliary signal. In a first aspect of the invention, the output of an optical amplifier is passed through a variable optical band-pass filter whose transmission characteristic is varied in accordance with the auxiliary signal, to modulate the spontaneous emission component contained in the optical amplifier output. In a second aspect of the invention, the output of the optical amplifier is separated by an optical branching device into a main optical signal and part of the spontaneous emission. The separated spontaneous emission component is modulated by being passed through a variable optical band-pass filter whose transmission characteristic is varied in accordance with the auxiliary signal, and then, the modulated spontaneous emission component is wavelength-division multiplexed with the main optical signal.

Auxiliary-signal transmission system

A control apparatus for an optical amplifier such as an erbium-doped optical-fiber (EDF) amplifier suppresses overshooting of ALC control at power on and at the time of input light restoration from an off condition, while ensuring quick starting. At power on and at the time of input light restoration from an off condition, an idling current (IDC) reference value generating circuit generates an IDC reference voltage that increases to a value sufficiently greater than a value in a normal operating condition with a time constant corresponding to a rise time of the EDF, and thereby controls a laser diode for pumping the EDF. The voltage may be set to a value larger than the value in the normal operating condition for a predetermined period of time by using a timer.

Growing community of inventors

Kawasaki, Japan

Yuji Tamura