Abstract: An optical amplifier for wavelength multiplexing optical transmission has an optical amplifier for amplifying wavelength-multiplexed signal light in which signal lights having wavelengths different from each other are wavelength-multiplexed and outputting the amplified wavelength-multiplexed signal light from an output terminal, and a light-removing portion which is disposed along the light path after the optical amplifier and removes spontaneous emission light existing between the wavelengths of the signal lights included in the amplified wavelength-multiplexed signal light.

Abstract: An optical amplifying apparatus which includes an optical amplifier, an optical attenuator and a controller. The optical amplifier amplifies a light signal having a variable number of channels. The optical attenuator passes the amplified light signal and has a variable light transmissivity. Prior to varying the number of channels in the light signal, the controller varies the light transmissivity of the optical attenuator so that a power level of the amplified light signal is maintained at an approximately constant level that depends on the number of channels in the light signal prior to the varying the number of channels. While the number of channels in the light signal is being varied, the controller maintains the light transmissivity of the optical attenuator to be constant.

Abstract: An optical fibre-amplifier and a transmission system with such a fibre-amplifier is proposed, in which the fibre-amplifier has an amplifying fibre-component with optical fibre-amplifier (2) and at least one optical component (6) which possesses a temperature behavior, which compensates the effects on the optical behavior of the fibre-amplifier.

Abstract: A heater system for heating an erbium-doped fiber amplifier (EDFA) of a fiber optic communication system operable in an environment. The heater system includes a pump laser for providing optical power to an erbium fiber in the EDFA. The pump laser is cooled by a thermoelectric cooler (TEC) when a predetermined maximum temperature is reached to maintain the temperature of the laser below the maximum temperature value. The temperature of the laser is sensed by a temperature sensor and is conveyed to a control circuit for generating a control signal. A heater unit is thermally connected to the erbium fiber and is controlled by the control signal in the event that the sensed temperature falls below a predetermined minimum value to maintain the temperature of the fiber above the minimum temperature value. A switch is connected between the control circuit, the TEC and the heater to automatically direct current to either the heater or the TEC depending on the sensed temperature.

Abstract: To obtain a uniform improving effect of secondary distortion over a wide frequency band with a very simple configuration and less power consumption in the distortion compensation circuit, that improves the secondary distortion circuit of an optical transmitter and a high-frequency amplifier used for a transmission line processing a high-frequency signal over a wide frequency band, such as a cable television(CATV).

Abstract: An optical amplifying apparatus which includes an optical amplifier, an optical attenuator and a controller. The optical amplifier amplifies a light signal having a variable number of channels. The optical attenuator passes the amplified light signal and has a variable light transmissivity. Prior to varying the number of channels in the light signal, the controller varies the light transmissivity of the optical attenuator so that a power level of the amplified light signal is maintained at an approximately constant level that depends on the number of channels in the light signal prior to the varying the number of channels. While the number of channels in the light signal is being varied, the controller maintains the light transmissivity of the optical attenuator to be constant.

Abstract: A display apparatus includes an image source that scans about two axes. To offset motion about a first of the axes during sweeps about the second axis, the apparatus includes a structure to produce offsetting motion about the first axis at a scanning rate equal to the twice-scanning rate about the second axis. The offsetting scan can be a ramp or other motion. In one embodiment, the offsetting motion is a resonant sinusoid. The offsetting motion may be produced by an auxiliary scanner such as a mechanical scanner, a piezoelectric scanner, a MEMs scanner or other scanner. Because the offsetting motion is very small, the auxiliary scanner can function with a very small scan angle.

Abstract: A multichannel fiber optic communication network incorporates multichannel fiber optical amplifiers having different functions but designed to use substantially identical gain flattening filters. This is achieved by designing the amplifiers to have total insertion losses such that their respective internal gains (internal gain=net gain+total insertion loss) are substantially the same, most preferably within 1 dB.

Abstract: A loss-less, optical add/drop multiplexer according to the present invention includes a rare earth-doped fiber amplifier integrated with a wavelength-selective fiber path coupled between two directional optical transfer devices for selectively adding and dropping optical signals from a multi-wavelength signal, such as a wavelength division multiplexed optical signal. One or more fiber gratings are disposed along the length of the rare earth-doped fiber amplifier or between segments of the rare earth-doped fiber so that at least one grating is used for reflecting each optical signal that is expected to be added to or dropped from the multi-wavelength optical signal. By using this configuration, appropriate amplification is provided to compensate for losses in the add, drop, and through paths.

Abstract: An optical fiber used as the active amplifying medium in a fiber laser is arranged to have a high insertion loss at an undesired frequency, while retaining a low insertion loss at a desired lasing frequency. In one embodiment, loss at a Raman-shifted frequency is introduced by using an optical fiber which has multiple claddings with an index profile that includes an elevated index region located away from the core, but within the evanescent coupling region of the core. A distributed loss, which can be enhanced by bending, is produced at the Raman frequency which effectively raises the threshold at which Raman scattering occurs in the fiber and therefore results in a frequency-selective fiber. In another embodiment, an absorbing layer is placed around the core region. The absorbing layer is chosen to have a sharp absorption edge so that it absorbs highly at the Raman-shifted wavelength, but minimally at the desired lasing wavelength.

Abstract: Optical systems of the present invention include a plurality of optical processing nodes in optical communication via at least one signal varying device. The signal varying devices includes an optical fiber suitable for facilitating Raman scattering/gain in a signal wavelength range and a pump energy source for providing pump energy in a plurality of pump wavelengths. The pump source provides sufficient pump energy in each pump wavelength to stimulate Raman scattering/gain in the optical fiber within the signal wavelength range. The pump wavelengths are selected such that the combined Raman gain resulting from the pump energy supplied by each pump wavelength produces a desired signal variation profile in the signal wavelength range. In addition, the pump energy supplied by at least one of the pump wavelengths can be varied to produce a controlled signal intensity variation profile over the signal wavelength range in the optical fiber.

Abstract: An optical fiber amplifier includes an input side wavelength combiner and an output side wavelength combiner arranged at an input side and an output side, respectively. An input optical signal is supplied from a transmission line to the input side wavelength combiner, while an output signal is supplied from the output side wavelength combiner to the transmission line. Further, an optical fiber is connected between the input side wavelength combiner and the output side wavelength combiner, an optical branch circuit is connected to the input side wavelength combiner and the output wavelength combiner and, a laser device is connected to the optical branch circuit and supplies an excited laser light beam to the optical branch circuit.

Abstract: An optical communication system having a transmitting station for outputting WDM(wavelength-division multiplexing) signal light, an optical fiber transmission line, a receiving station, and an optical repeater including an optical amplifier. The transmitting station includes a supervisory circuit for detecting the number of channels of the WDM signal light and transmitting supervisory information including the number of channels to the optical repeater. The optical repeater further includes a circuit for controlling the optical amplifier so that the output level of the optical amplifier becomes a target level. The target level is set according to the supervisory information. According to the structure, it can be possible to provide a system which can easily respond to a change in the number of WDM channels.

Abstract: In the optical amplifier of the present invention, a part of signal light inputted to an input connector is branched out by an optical coupler, whereby its power is detected by a light-receiving device. According to the power of input signal light detected by the light-receiving device, the temperature of an amplification optical fiber is controlled by a temperature control section by way of a Peltier device. On the other hand, a part of the signal light outputted from an output connector is branched out by an optical coupler, whereby its power is detected by a light-receiving device. The power of pumping light supplied to the amplification optical fiber from an pumping light source 152 is controlled by an output control section 162 such that the power of output signal light detected by the light-receiving device becomes a predetermined target value.

Abstract: An apparatus and method are described for exploiting almost the full almost 25 THz of bandwidth available in the low-loss window in optical fibers (from 1430 nm to 1620 nm) using a parallel combination of optical amplifiers. The low-loss window at about 1530 nm-1620 nm can be amplified using erbium-doped fiber amplifiers (EDFAs). However, due to the inherent absorption of the erbium at shorter wavelengths, EDFAs cannot be used below about 1525 nm without a significant degradation in performance. For the low-loss window at approximately 1430-1530 nm, amplifiers based on nonlinear polarization in optical fibers can be used effectively. A broadband nonlinear polarization amplifier (NLPA) is disclosed which combines cascaded Raman amplification with parametric amplification or four-wave mixing. In particular, one of the intermediate cascade Raman order wavelengths .lambda..sub.r should lie in close proximity to the zero-dispersion wavelength .lambda..sub.0 of the amplifying fiber.

Abstract: A return-to-zero pulse optical communication system includes fast saturable absorber means (F1,DSF) to provide substantially zero average dispersion in a single amplifier span (SIF,DSF) to reduce the effect of timing jitter an provide considerably enhanced propagation distances.

Abstract: A system for amplifying separate optical signals traveling in a forward path and a reverse path over an optical communications system used for CATV program distribution. A first and second optical circulator, each having a first, second, and third port, are connected to respective opposite sides of a bi-directional amplifier. The first port of the first circulator inputs a first optical signal traveling in the forward path. The second port of the first circulator is coupled to an input/output port of the amplifier. The third port of the first circulator outputs an amplified second signal traveling in the reverse path. The second circulator is similarly connected to the side of the amplifier. A first and second signal/signal WDM coupler, each having a pass port P, an add port A/D, and a common port C, are coupled to the first and second optical circulators, respectively.

Abstract: A multi-amplification path optical amplifier including a first amplification path for propagating and amplifying a first in-band optical communication signal, including a spectrally selective filter for substantially blocking the propagation and amplification of an out-of-band optical communication signal along the first amplification path, and a second amplification path for propagating and amplifying a second in-band optical communication signal, including a spectrally selective filter for substantially blocking the propagation and amplification of an out-of-band optical communication signal along the second amplification path, wherein the location of the spectrally selective filters in each respective amplification path is selected so that a target noise figure performance and a target output power performance can be obtained from the device. The spectrally selective insertion losses suppress crosstalk or optical leakage that gives rise to multipath interference, return loss, and self oscillation.

Abstract: An optical amplifier has an optical amplifying medium, a pump light source outputting pump light, and a first optical coupler for supplying the pump light to the optical amplifying medium. A probe light source outputs probe light having a wavelength included in an amplification band, a second optical coupler supplies the probe light to the optical amplifying medium, and detectors detect the powers of input signal light and the probe light, respectively. A control unit controls the power of the probe light according to outputs from the detectors. This structure makes it possible to provide an optical amplifier which can reduce the wavelength dependence of gain.

Abstract: An optical transmission system having a linear repeater section that performs linear amplification of an optical signal, in which some functional redundancy is introduced to improve the reliability of long-distance signal transmission. The optical transmission line is segmented by regenerative repeater devices into a plurality of linear repeater sections, in each of which a plurality of linear optical amplifiers are deployed. The regenerative repeater devices have a signal regeneration unit that regenerates the received optical signals to compensate for their deterioration. The present invention eliminates RSOH termination and insertion functions from the regenerative repeater devices connected to at least one end of each linear repeater section. Further, the present invention deploys a signal regeneration unit in parallel with a linear optical amplifier within each linear repeater section.

Abstract: An optical amplifier amplifies a wavelength-division-multiplexed optical input signal composed of optical signals having different wavelengths such that the output level of each of the optical signal is always optimized and such that the difference between the gains of the amplifier on the optical signals is minimized when the number of optical signals is two. The output level of the amplifier is controlled according to the number of the optical signals, to optimize the output level of each of the optical signals.

Abstract: An optical amplifier is disclosed having substantially uniform spectral gain. The amplifier comprises a variable optical attenuator coupled between first and second segments of active optical fiber. The attenuation of the optical attenuator is adjusted in accordance with the optical power input to the amplifier to thereby obtain substantially flattened gain. Alternatively, the attenuator can be controlled based on the respective gains associated with the first and second segments of optical fiber. For example, the attenuator can be adjusted so that so that the sum of the two gains remains substantially constant, a condition that also yields flat spectral gain. Further, optical powers associated with first and second wavelengths of amplified stimulated emission (ASE) light output from the amplifier can be used to adjust the attenuation of the optical attenuator.

Abstract: A multi-wavelength light amplifier includes a first-stage light amplifier which has a first light amplifying optical fiber amplifying a light input, a second-stage light amplifier which has a second light amplifying optical fiber amplifying a first light output from the first-stage light amplifier, and an optical system which maintains a second light output of the second-stage light amplifier at a constant power level. The first-stage and second-stage light amplifiers have different gain vs wavelength characteristics so that the multi-wavelength light amplifier has no wavelength-dependence of a gain thereof.

Abstract: A wavelength multiplexing optical transmitting apparatus includes a plurality of optical transmitters for transmitting optical signals having mutually different wavelengths, a wavelength multiplexing circuit for wavelength multiplexing optical signals, an optical amplifier for directly amplifying the wavelength multiplexed optical signal and for producing an amplified multiplexed optical signal, an optical signal counting detector for branching the amplified multiplexed optical signal into signals of the respective wavelengths and for detecting the number of optical signals presently being transmitted, and an optical amplifier control circuit for controlling an output from the optical amplifier according to the number of optical signals; the optical amplifier includes a fiber made of a material to which a rare earth element is added and an excitation light to the fiber; the optical amplifier control circuit includes an excitation light control circuit for controlling an intensity of the excitation light accor

Abstract: A semiconductor optical amplifier which has a good extinction ratio and a simple structure includes an optical waveguide having at least a curved portion. The optical waveguide has light input and output ends offset from each other to keep optical fibers out of alignment with each other at respective opposite ends of the optical waveguide.

Abstract: An optical amplifier is disclosed having substantially uniform spectral gain. The amplifier comprises a variable optical attenuator coupled between first and second segments of active optical fiber. The attenuation of the optical attenuator is adjusted in accordance with the optical power input to the amplifier to thereby obtain substantially flattened gain. Alternatively, the attenuator can be controlled based on the respective gains associated with the first and second segments of optical fiber. For example, the attenuator can be adjusted so that so that the sum of the two gains remains substantially constant, a condition that also yields flat spectral gain. Further, optical powers associated with first and second wavelengths of amplified stimulated emission (ASE) light output from the amplifier can be used to adjust the attenuation of the optical attenuator.

Abstract: In accordance with the invention, a temperature-dependent rare earth doped waveguide optical amplifier is compensated by a temperature-dependent loss filter. The filter characteristics are designed to be temperature-dependent filters so that the gain characteristic of the amplifier is compensated over a practical operating temperature range. In essence, the amplifier comprises a length of optical waveguide for transmitting optical signals, a rare earth doped amplifying region in the waveguide for amplifying the transmitted optical signals, a pumping source for optically pumping the amplifying region, and a temperature-dependent loss filter. A typical design compensates an EFDA to a variation of less than 1 dB over a temperature range of -40.degree. C. to 85.degree. C. and a spectral range of at least 20 nm.

Abstract: In an optically amplified multi-wavelength optical fiber communication system, deleterious effects due to channel addition/removal can be reduced or avoided if the optical amplifiers are "overpumped", that is to say, the system is selected such that at least 70%, preferably 90% or more, of the pump power that is introduced into the amplifier fiber is unabsorbed in the amplifier fiber.

Abstract: An optical waveguide amplifier is formed to include an adiabatic region disposed between an input single mode waveguide and a large area, multimode gain region. The utilization of the adiabatic region allows for a single mode signal to be supported and provides for a larger gain area to be formed, thus providing a larger gain and higher output power than conventional prior art waveguide amplifier arrangements.

Abstract: A semiconductor optical amplifier includes in integrated form a linear response attenuation segment in series between first and second amplification segments. The amplifier can be used to implement a high-speed wavelength converter that can be used with advantage in an optical telecommunication system.

Abstract: In an optical amplifier, multiplexed light beams inputted to an optical amplifying medium are guided and the optical amplifying medium is excited by an exciting source to change the mu-factor. Part of multiplexed light beams amplified by the optical amplifying medium are branched by an optical coupler, only a probe light beam is separated from the branched multiplexed light beams by means of a light separating unit, and the probe light beam is detected by a light receiving unit. A controller controls an amount of operation of the exciting source on the optical amplifying medium such that an output of the light receiving unit (an output of the probe light beam) becomes constant, thereby controlling the output of the probe light beam and the outputs of the multiplexed signal light beams to constant values.

Abstract: A doped fiber amplifier which provides bidirectional pumping to amplify a signal light, and reduces instability of gain caused by the bidirectional pumping. The doped fiber amplifier includes a rare earth element doped optical fiber, a first light source and a second light source. The optical fiber has first and second ends, with the signal light propagating through the optical fiber from the first end to the second end. The first light source provides pump light which propagates in the optical fiber from the first end to the second end and is at a first wavelength. The second light source provides pump light which propagates in the optical fiber from the second end to the first end and is at a second wavelength. The first wavelength is different from the second wavelength. The pump light provided by the first and second light sources causes the signal light to be amplified as the signal light propagates through the optical fiber.

Abstract: An optical amplifying apparatus which includes an optical amplifier, an optical attenuator and a controller. The optical amplifier amplifies a light signal having a variable number of channels. The optical attenuator passes the amplified light signal and has a variable light transmissivity. Prior to varying the number of channels in the light signal, the controller varies the light transmissivity of the optical attenuator so that a power level of the amplified light signal is maintained at an approximately constant level that depends on the number of channels in the light signal prior to the varying the number of channels. While the number of channels in the light signal is being varied, the controller maintains the light transmissivity of the optical attenuator to be constant.

Abstract: An optical communication system having a transmitting station for outputting WDM(wavelength-division multiplexing) signal light, an optical fiber transmission line, a receiving station, and an optical repeater including an optical amplifier. The transmitting station includes a supervisory circuit for detecting the number of channels of the WDM signal light and transmitting supervisory information including the number of channels to the optical repeater. The optical repeater further includes a circuit for controlling the optical amplifier so that the output level of the optical amplifier becomes a target level. The target level is set according to the supervisory information. According to the structure, it can be possible to provide a system which can easily respond to a change in the number of WDM channels.

Abstract: An improved method of measurement of noise figure and gain of optical amplifiers is based on transforming the amplifier into an oscillator by applying optical feedback with known loss. The feedback consists of a tunable filter for wavelength control and of a variable attenuator for gain control. Measuring the output power at a given wavelength and the noise characteristics of the output signal, either with an optical spectrum analyzer or with a set of tunable filters and a power meter, provides data for full characterization of the optical amplifier. Another method is disclosed that utilizes the self-heterodyne setup and electrical spectrum analyzer to measure the spectral line width of the lasing amplifier, from which the noise figure is derived.

Abstract: A laser amplifier, an optical system comprising such a laser amplifier and a method of forming such a laser amplifier for obtaining polarization independent amplification over a large wavelength region. The optical amplifier comprises an active region that is formed on a semiconductor substrate (6). The active layer has been formed through growing of quantum well layers (13, 14, 15, 16) alternating with barrier layers (12). The well layers comprise well layers of a first type (14, 15, 16) having tensile strain together with or without well layers of a second type having compressive strain (13). At least one of the well layers of one type (16) has been grown to a different width and/or with a different material composition than the other well layers of the same type (14, 15).

Abstract: An erbium doped fiber amplifier having one pumping source which outputs pump power so as to excite a light signal, the amplifier including: a first erbium doped fiber for receiving an excitation light signal input from the pumping source, and amplifying a transmitted light signal input from an input stage; a first wavelength division multiplexer located at an output of the first erbium doped fiber, for inputting the excitation light signal input from the pumping source to the first erbium doped fiber, the first multiplexer also receiving the transmitted light signal amplified from the first erbium doped fiber and outputting it to a next stage; a dispersion compensation fiber at an output of the first wavelength division multiplexer for compensating for loss caused due to the dispersion characteristics of the transmitted light signal; a second wavelength division multiplexer located at an output of the dispersion compensation fiber, for receiving the input transmitted light signal and the excitation light sign

Abstract: An Erbium doped fiber amplifier (EDFA) is placed in a laser cavity to clamp the gain of the amplifier. The laser cavity is preferably formed to minimize the effects of relaxation oscillations and of spectral hole burning. In a preferred embodiment, the laser cavity supports a lasing wavelength which makes the saturation energy at the laser wavelength less than that at the signal wavelengths. In an erbium doped fiber implementation, the laser wavelength is shorter than that of the signal wavelengths and is separated from them by no more than approximately 75% of the width of the spectral hole. The compounding of relaxation oscillations may be substantially eliminated by varying the length of the fiber within each laser cavity within a system to change the photon round-trip time within each cavity.

Abstract: An optical fiber amplifier with an absorber, including a first amplification unit for amplifying an input signal light, using first pump light; an absorption unit for separating the signal light and the pump light from the output light of the first amplification unit and absorbing a light signal in a wavelength range; and a second amplification unit for amplifying the signal light output by the absorption unit, using second pump light. The optical fiber amplifier can be easily manufactured by adding an absorber, an erbium doped fiber, to a conventional optical fiber amplifier. The characteristics of the optical fiber amplifier can be easily changed by controlling the length of the absorber.

Abstract: Optical signals transmitted from optical transmission panels are received by photodetectors, which detect the number of actually transmitted optical signals. A control signal depending on the number of optical signals detected is supplied to an optical amplifier. The intensity of a combined optical signal amplified by the control signal is controlled by controlling a current supplied to a pumping light source. Information representative of the number of optical signals detected is superposed onto the amplified optical signal by generating the current supplied to the pumping light source as a sine-wave signal depending on the detected number of optical signals. In a downstream optical repeater, the information representative of the number of optical signals is extracted, and the optical signal is amplified, after which the information representative of the number of optical signals is superposed again onto the amplified optical signal for transmission.

Abstract: A doped fiber amplifier which provides bidirectional pumping to amplify a signal light, and reduces instability of gain caused by the bidirectional pumping. The doped fiber amplifier includes a rare earth element doped optical fiber, a first light source and a second light source. The optical fiber has first and second ends, with the signal light propagating through the optical fiber from the first end to the second end. The first light source provides pump light which propagates in the optical fiber from the first end to the second end and is at a first wavelength. The second light source provides pump light which propagates in the optical fiber from the second end to the first end and is at a second wavelength. The first wavelength is different from the second wavelength. The pump light provided by the first and second light sources causes the signal light to be amplified as the signal light propagates through the optical fiber.

Abstract: An optical amplifying apparatus which includes an optical amplifier, an optical attenuator and a controller. The optical amplifier amplifies a light signal having a variable number of channels. The optical attenuator passes the amplified light signal and has a variable light transmissivity. Prior to varying the number of channels in the light signal, the controller varies the light transmissivity of the optical attenuator so that a power level of the amplified light signal is maintained at an approximately constant level that depends on the number of channels in the light signal prior to the varying the number of channels. While the number of channels in the light signal is being varied, the controller maintains the light transmissivity of the optical attenuator to be constant.

Abstract: In a gain-controlled erbium-doped optical amplifier, gain control is achieved by clamping the gain of a laser cavity to be equal to the overall cavity loss and by fixing the resonant wavelength of the amplifier to be at a first wavelength. When an optical signal to be amplified having a second wavelength different from the first wavelength passes through the amplifier the gain experienced by the signal depends entirely on the gain of the cavity, and not on the intensity of the signal. If the first wavelength is arranged to be at the peak of the sum of the absorption and emission cross sections of erbium, the amplifier exhibits minimum sensitivity to ambient changes in temperature.

Abstract: A dual-stage doped fiber amplifier is provided which utilizes a single pump laser and a passive power splitter to pump both amplifier stages. The passive splitter couples a first portion of the power output of the single pump laser to a first stage amplifier and a second portion of the pump power to the second stage. In this manner, the performance characteristics of the amplifier can be controlled by utilizing a single pump source.

Abstract: An optical amplifier prevents generation of an optical surge when an input signal to the optical amplifier is interrupted. A synthesized signal of an input signal light and a pumping light is input to an optical amplifying medium. An input signal light interruption detecting circuit detects an interruption of the input signal light. A variable attenuator element is provided on a signal light input side of the optical amplifying medium so as to attenuate the input signal light. The variable attenuator element is controlled based on an output of the input signal light interruption detecting circuit so that a degree of attenuation of the variable attenuator element is increased when the input signal light is interrupted and the degree of attenuation is gradually decreased when the input signal light returns.

Abstract: The amplifier is a two-stage amplifier in which dispersion compensation and WDM channel equalization are carried out using a plurality of in-waveguide Bragg gratings placed between the two stages. The first stage has a gain able to raise the intensity of WDM optical communications signals to a high enough level that after dispersion compensation and equalization, the signals fed into the second stage nearly or substantially saturate the second stage amplifier. The noise figure signal-to-noise ratio is thereby of good quality since there are no significant losses at the signal input of the signal into the optical amplifier. Erbium-doped optically pumped fiber amplifiers are used for the two stages. An add/drop filter can be appended to the end of the conditioning Bragg gratings. Residual optical signal from the fiber Bragg grating may be used to optically pump another amplifier for amplifying longer wavelength optical signals.

Abstract: An optical amplifying apparatus which includes an optical amplifier, an optical attenuator and a controller. The optical amplifier amplifies a light signal having a variable number of channels. The optical attenuator passes the amplified light signal and has a variable light transmissivity. Prior to varying the number of channels in the light signal, the controller varies the light transmissivity of the optical attenuator so that a power level of the amplified light signal is maintained at an approximately constant level that depends on the number of channels in the light signal prior to the varying the number of channels. While the number of channels in the light signal is being varied, the controller maintains the light transmissivity of the optical attenuator to be constant.

Abstract: 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.

Abstract: A monitoring apparatus for an optical fiber amplifier includes a branch member, an optical filter, a light-receiving element, and a detector. The branch member branches reflected light obtained by reflecting, by an output portion, output light from an optical fiber amplifier for directly amplifying an optical signal. The optical filter removes a signal wavelength component from the reflected light branched by the branch member. The light-receiving element receives the reflected light output from the optical filter from which the signal wavelength component is removed. The detector outputs a detection signal representing an abnormality on a transmission path when the output level of the light-receiving element is a predetermined level or higher.

Abstract: An optical amplifier is disclosed having substantially uniform spectral gain. The amplifier comprises a variable optical attenuator coupled between first and second segments of active optical fiber. The attenuation of the optical attenuator is adjusted in accordance with the optical power input to the amplifier to thereby obtain substantially flattened gain. Alternatively, the attenuator can be controlled based on the respective gains associated with the first and second segments of optical fiber. For example, the attenuator can be adjusted so that so that the sum of the two gains remains substantially constant, a condition that also yields flat spectral gain. Further, optical powers associated with first and second wavelengths of amplified stimulated emission (ASE) light output from the amplifier can be used to adjust the attenuation of the optical attenuator.