Abstract: PROBLEMS To enable a single optical amplifier to function as a boost amplifier and a preamplifier. MEANS FOR SOLVING PROBLEMS By using a wavelength routing, a single optical amplifier can have the function of a boost amplifier and the function of a preamplifier. Moreover, by attenuating a transmission signal in advance, it is possible to adjust a gain difference required in the boost amplifier and the preamplifier.

Abstract: An optical demultiplexer (13, 30) for wavelength division multiplex WDM optical radiation comprising a plurality of wavelength channels (Ch1 . . . Ch16) spaced over a wavelength spectrum said demultiplexer being for separating the WDM radiation into individual wavelength channels is described. The demultiplexer comprises a first demultiplexer (12) for dividing the W-DM radiation into a plurality of sub-bands (Ch1 . . . Ch4, Ch5 . . . Ch8, Ch9 . . . Ch12, Ch13 . . .

Abstract: An optical amplifier apparatus for amplifying a wavelength division signal light includes a detector for detecting an inputted wavelength division signal light, a dispersion compensator for compensating for a dispersion of the inputted wavelength division signal light, an optical amplifier for amplifying the inputted wavelength division signal light after compensation by stimulated emission of an optical gain medium including a rare-earth element, a propagation delay detector for detecting a propagation delay time of the wavelength division signal light between the detector and the optical amplifier, and a controller for controlling the gain of the optical amplifier on the basis of the propagation delay time such that the change of the gain of the optical amplifier is adjusted by the propagation delay time.

Abstract: An electronic circuit for controlling a laser system consisting of a pulse source and high power fiber amplifier is disclosed. The circuit is used to control the gain of the high power fiber amplifier system so that the amplified output pulses have predetermined pulse energy as the pulse width and repetition rate of the oscillator are varied. This includes keeping the pulse energy constant when the pulse train is turned on. The circuitry is also used to control the temperature of the high power fiber amplifier pump diode such that the wavelength of the pump diode is held at the optimum absorption wavelength of the fiber amplifier as the diode current is varied. The circuitry also provides a means of protecting the high power fiber amplifier from damage due to a loss of signal from the pulse source or from a pulse-source signal of insufficient injection energy.

Abstract: A pumping unit supplies pumping light to a fiber connecting medium; a light monitoring unit detects light power of multiple-wavelength light; and a control unit controls the pumping light based on light power detected by the light monitoring unit and connecting medium information indicating optical characteristics in the connecting medium. The connecting medium information includes information indicating a fiber type of the fiber connecting medium, information indicating a length of the fiber connecting medium, an average fiber loss coefficient of the fiber connecting medium and an intra-station loss value.

Abstract: An embodiment of the invention comprises determining a gain tilt based on power measurements from a power measurement block, determining a noise figure penalty based on the gain tilt, determining a gain tilt compensation to compensate for the gain tilt taking into account the noise figure penalty, and communicating the gain tilt compensation to an amplifier block to apply the gain tilt compensation to subsequently received wavelengths.

Abstract: It is described an optical amplification device for receiving an optical input signal and transmitting an amplified optical output signal on the basis of the optical input signal comprising an optical amplifier that comprises an input and an output. An optical gain control unit is connected to the output path of the optical amplifier and the optical gain control unit is connected to the input path of the optical amplifier. The optical gain control unit is configured to control the gain of the optical output signal. Additionally, an electrical gain control unit is connected to the output path of the optical amplifier. The electrical gain control unit is also connected to the input path of the optical amplifier. The electrical gain control unit is configured to control the gain of the optical output signal. By providing both an electrical gain control unit and an optical gain control unit, a control characteristic can be improved.

Abstract: The present invention provides a multi-stage optical amplifier including a high SN ratio and a method of controlling the same. A multi-stage optical amplifier is configured such that the gain of an amplifying unit in a first stage is greater than that of an amplifying unit in another stage. Therefore, it is possible to increase signal components that have been reduced due to spontaneously emitted light in the first stage, and thus relatively reduce noise. As a result, the obtained signals including a high SN ratio can be maintained in another stage, and it is possible to obtain a high SN ratio.

Abstract: A Self-adapting feed forward control apparatus in an optical amplifier includes a feed forward controller for collecting target output power (Pout) and controlling drive current of a pump laser in the optical amplifier; a feedback controller for calculating target output power (Pt) and collecting actual output power (Pout), calculating deviation between (Pt) and (Pout), and controlling drive current of the pump laser; and a parameter estimator for collecting power target, output power and summation of output signal of the feed forward controller and feedback controller, and estimating the feed forward parameter and updating the parameter of the feed forward controller. The apparatus can automatically correct the feed forward control parameters according to the variation of EDFA parameters due to environmental condition changes or device aging.

Abstract: This specification describes technologies relating to controlling optical amplifiers. In one implementation, an optical amplifier is provided. The optical amplifier includes a light amplifying medium for receiving an input optical signal and outputting an output amplified signal; a first measuring block for measuring a change in power of the input signal; a pump laser for supplying pump light to the light amplifying medium; and an electronic control for controlling the power of the pump light in response to the measured change in power of input signal to provide an output amplified signal having a substantially constant power for one or more changes in the power of the input signal.

Abstract: A controller for reducing a transient variation of gain of an optical amplifier is disclosed. The controller includes a control circuit adapted to generate an electrical signal mimicking optical gain transient variation upon an abrupt change in input loading conditions. The electrical signal is applied to a variable optical attenuator disposed downstream of the active optical fiber of the optical amplifier. The control circuit can be realized in a variety of ways, but preferably it includes a logarithmic amplifier and a high-pass filter sequentially connected. The logarithmic amplifier is connected to an input tap/photodetector, and the high-pass filter is connected to the variable optical attenuator.

Abstract: An optical network device of a passive optical network is introduced. The optical network device includes a light source, a control unit, and a variable optical attenuator. The light source can generate an optical signal. The control unit can generate a magnetic signal based on a control signal capable of providing information relating to a distance between the optical network device and an optical line termination. The variable optical attenuator can adjust a polarization angle of the optical signal based on the magnetic signal.

Abstract: In an optical transmission system, a controller acquires a noise light loss value, which indicates a loss that noise light output from an upstream-side optical amplifier undergoes during propagation to a downstream-side optical amplifier through an optical loss medium, and a signal beam loss value, which indicates a loss that a signal beam output from the upstream-side optical amplifier undergoes during propagation to the downstream-side optical amplifier through the optical loss medium, obtains, as a loss difference, a difference between the noise light loss value and the signal beam loss value and, when setting up the downstream-side optical amplifier, determines the gain of the downstream-side optical amplifier by compensating the loss difference.

Abstract: A two-way optical amplifier system amplifies upstream and downstream optical signals in a passive optical network (PON). The downstream optical amplifier system includes an optical amplifier (EDFA), configured and arrange to amplify the downstream optical transport signal.

Abstract: The invention relates to a regulatable optical amplifier which has at least two series-connected amplifier groups, each amplifier group having a regulating device. Connected upstream of the optical amplifier is a power monitor device for detecting changes in the input power, whose electrical output is connected both to the first regulating device and to the second regulating device. In line with the invention, the first and second regulating devices have a control line inserted between them which comprises a series circuit containing a high-pass filter, a delay and signal-shaping unit and a feed-forward control unit for generating a correction signal for the second regulating device. In this arrangement, the high-pass filter has a cut-off frequency which corresponds approximately to the cut-off frequency of the first amplifier group.

Abstract: An optical amplifier includes an input port, an output port, an amplification medium, a light source, a monitor, and a controller. The amplification medium with which doped an rare-earth element for optical amplification is allocated on an optical path between the input port and the output port. The light source supplies the amplification medium with an excitation light. The monitor monitors a total power of an optical signal of each wavelength according to a monitor period which is longer than a transient response time of the amplification medium. The controller controls the light source so that a power of the excitation light is constant when a monitor value of the monitor is equal to or smaller than a predetermined threshold value and controls the light source so that an optical gain in the amplification medium is constant when the monitor value is larger than the predetermined threshold value.

Abstract: A Raman amplifier inputs pump light into an optical fiber (transmission path) through which an optical signal passes, to amplify the optical signal. An optical receiving unit is provided downstream of the Raman amplifier and monitors the power of the optical signal amplified by the Raman amplifier. A calculating unit determines Raman amplification gain based on the power of the optical signal monitored by the optical receiving unit, and calculates the power of a noise component included in the optical signal based on the gain. The calculating unit, in real-time, calculates the power, which varies in complicated manners depending on conditions, and outputs information concerning to the power to another apparatus at a frequency on the order of milliseconds.

Abstract: 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.

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 amplification device which includes first and second optical amplifiers, and a controller. The first optical amplifier receives a light and amplifies the received light. The second optical amplifier receives the light amplified by the first optical amplifier, and amplifies the received light. When a level of the light received by the first optical amplifier changes by ?, the controller controls a level of the light received by the second optical amplifier to change by approximately ??. In various embodiments, the controller causes the sum of the gains of the first and second optical amplifiers to be constant. In other embodiments, the optical amplification device includes first and second optical amplifier and a gain adjustor. The gain adjustor detects a deviation in gain of the first optical amplifier from a target gain, and adjusts the gain of the second optical amplifier to compensate for the detected deviation.

Abstract: The specification describes an improved approach to suppressing fast transients in optical amplifier systems. The approach relies on operating the amplifier in an automatic power-mode control with an extra loss component. It is applicable to optical amplifiers based on rare earth amplifier media, such as erbium doped fiber amplifiers (EDFAs).

Abstract: 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.

Abstract: According to a WDM optical transmission system of the present invention, wavelength numbers information of a WDM signal light output from an upstream side optical amplifying unit to a transmission path fiber, and signal output level information thereof are transmitted to a downstream side optical amplifying unit utilizing a supervisory control light. In the downstream side optical amplifying unit, a loss (span loss) in the transmission path fiber is computed using the upstream side signal output level information and downstream side signal input level information, so that a gain to be set for a downstream side optical amplifier is calculated based on the computed loss, and also, the gain is corrected based on a difference between a target value of the signal output level computed using the wavelength numbers information and an actual measurement value thereof, so that the optical amplifier is controlled in accordance with the post-corrected gain.

Abstract: In some embodiments, the present invention provides an apparatus and process wherein excess stored optical energy is removed from one or more stages in a fiber-amplifier, in order to stabilize the gain and obtain a constant level of energy per pulse. In some embodiments, a method of the invention includes providing a gain fiber, optically pumping the gain fiber using pump light, amplifying seed-signal pulses having a signal wavelength using the gain fiber to obtain amplified output pulses, and automatically limiting a gain of the gain fiber. In some embodiments, an apparatus of the invention includes a gain fiber, a source of pump light coupled to the gain fiber, a source of seed-signal pulses having a signal wavelength coupled to the gain fiber, wherein the gain fiber outputs amplified signal pulses, and an automatic-gain-control mechanism configured to limit gain of the gain fiber.

Abstract: An optical amplifier includes a detecting section configured to detect a part of an input optical signal from a first node on an input side optical fiber; and a rare earth element doped optical fiber amplifier configured to amplify a remaining part of the input optical signal supplied from the input side optical fiber by using an excitation optical signal supplied from a second node and to output the amplified optical signal as an output optical signal to an output side optical fiber. A control unit controls the excitation optical signal based on the detected part of the input optical signal by the detecting section without real time control based on the output optical signal.

Abstract: 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.

Abstract: A two-way optical amplifier system amplifies upstream and downstream optical signals in a passive optical network (PON). The downstream optical amplifier system includes an optical amplifier (EDFA), configured and arrange to amplify the downstream optical transport signal.

Abstract: A system and method for controlling the gain of an optical amplifier receiving one or more optical input signal channels at a first end include a source for generating a gain control signal, which is input to the optical amplifier at the opposite end to the input signal channels. The gain control signal is generated at a power level that produces stimulated Brillouin scattering (SBS) in the optical amplifier.

Abstract: The present invention relates to an optical amplifier with a structure for more effectively suppressing the over/undershoot in transient responses in high-speed AGC. This optical amplifier is an optical device for amplifying signal light inputted therein, and comprises a rare-earth-element-doped optical fiber, an optical coupler, a light-receiving section, a pumping light source, and a control section. In particular, as a typical structure of the optical amplifier, the rare-earth-element-doped optical fiber has a cutoff wavelength ?c set longer than the pumping light wavelength ?p but shorter than the signal light wavelength ?s, and mainly allows a pumping light component in a fundamental mode to propagate therethrough.

Abstract: Optical amplifier transient control methods and apparatus which limit the extent of cumulative transient gain errors in the rapid control of multiple optical amplifiers in a communication system. In an exemplary embodiment, if the input power to an optical amplifier drops below a predetermined threshold, the gain of the amplifier is set to clamp the output power of the amplifier to its initial level less the threshold, thereby preventing the continuous growth of gain error. This is based on the assumption that once the input power goes below the threshold, it should no longer go above the threshold until the transient condition is corrected. The present invention can operate to handle down-as well as up-transient events and is not amplifier technology dependent.

Abstract: Provided is an all-optical gain-clamped fiber amplifier, comprising transmission and isolation means for periodically transmitting an optical signal or reflecting amplified spontaneous emission (ASE) back to a gain medium. The transmission and isolation means can be embodied by an optical interleaver or a number of optical fiber Bragg gratings. Accordingly, an optical signal can be amplified across the entire C-band, and an ASE reflector-based gain-clamped fiber amplifier having a wider dynamic range than conventional amplifiers can be implemented.

Abstract: An automated optical transport system is provided which provides for automatic discovery of system components, automatic inventory of system components, automatic topology detection, automatic provisioning of channels, and automatic characterization and tuning of system components and fiber. The invention provides automation capability through inclusion of management card capabilities at each station which communicates through a reverse propagating service channel. Dynamic and propagation direction independent segments are provided in conjunction with a token-based scheme to repeatedly tune, update and monitor the transport system.

Abstract: In an optical transmission system, a controller acquires a noise light loss value, which indicates a loss that noise light output from an upstream-side optical amplifier undergoes during propagation to a downstream-side optical amplifier through an optical loss medium, and a signal beam loss value, which indicates a loss that a signal beam output from the upstream-side optical amplifier undergoes during propagation to the downstream-side optical amplifier through the optical loss medium, obtains, as a loss difference, a difference between the noise light loss value and the signal beam loss value and, when setting up the downstream-side optical amplifier, determines the gain of the downstream-side optical amplifier by compensating the loss difference.

Abstract: A method of operating an amplifier system includes providing a pump signal at a pump wavelength. The pump signal is a function of a pump power. The method also includes providing an input signal at a signal wavelength and coupling the pump signal and the input signal to an optical amplifier. The optical amplifier includes a gain medium characterized by a gain value at the signal wavelength. The method further includes amplifying the input signal to provide an output signal, detecting a feedback signal related to the gain value, and modifying the pump power based on the detected feedback signal.

Abstract: A high-speed bit stream interface module interfaces a high-speed communication media to a communication Application Specific Integrated Circuit (ASIC) via a Printed Circuit Board (PCB). The high-speed bit stream interface includes a line side interface, a board side interface, and a signal conditioning circuit. The signal conditioning circuit services each of an RX path and a TX path and includes a limiting amplifier and a clock and data recovery circuit. The signal conditioning circuit includes an AGC loop, an equalizer, and an equalizer feedback loop. The AGC loop includes a gain path and a feedback path that couples to the output of the equalizer. The equalizer feedback loop couples to the output of the equalizer and produces spectral shaping control settings that the equalizer uses to produce an equalized high-speed serial bit stream at an equalizer output.

Abstract: An optical transmission apparatus for amplifying and relaying a wavelength-division-multiplexed optical signal includes (1) a variation-detecting unit which detects varying speed of input power of the wavelength-division-multiplexed optical signal and compares the varying speed with a set value, (2) an optical amplifying unit which amplifies the wavelength-division-multiplexed optical signal at a fixed amount of amplification, (3) a variable optical attenuating unit which variably attenuates the wavelength-division-multiplexed optical signal, (4) and a controlling unit which controls attenuation amount of the variable optical attenuating unit in accordance with the varying speed.

Abstract: 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.

Abstract: A photo amplifying apparatus for amplifying wavelength division multiplexed signals includes a specific wavelength measuring unit for measuring a specific wavelength at a measuring point, a total power measuring unit for measuring all wavelengths at the measuring point, and an output control unit for controlling the output of the photo amplifying apparatus based on the light power measured by the specific wavelength measuring unit and the total power measuring unit. Since the photo amplifying apparatus measures both the specific wavelength and all wavelengths, the photo amplifying apparatus can determine change in the number of multiplexed wavelengths and the gain gradient of the photo signals, and can properly control its output level.

Abstract: The present invention relates to an optical amplifier provided with a plurality of optically cascade-connected amplification units and also with a structure for enabling suppression of transient gain variations as a whole. Each of the plurality of amplification units in the optical amplifier has a pumping light source and an amplifying optical fiber, and at least one selected from the plurality of amplification units includes a timing adjustment system for temporally moving back or forth the variation timing of pumping light power accompanying the signal light power variation due to the variation of the number of signal channels, with respect to the variation timing of signal light power at a light incident end of the amplifying optical fiber contained in the own amplification unit.

Abstract: In a wavelength-division-multiplexing optical transmission system in which optical-node apparatuses that perform relay transmission of wavelength-division-multiplexed light are located at specified nodes in a main optical transmission path, an optical amplifier switches level control to constant-gain control when there is a notification of a change in the number of multiplexed wavelengths, and then after a specified amount of time restarts level control so that the level becomes a target level that corresponds to the actual number of wavelengths.

Abstract: An optical amplifier includes a rare-earth doped optical fiber or rare-earth doped optical waveguide serving as an amplification medium where rare-earth ions have been doped in its core and/or clad, an excitation mechanism for exciting the amplification medium, and a plurality of optical resonator that causes laser oscillation at a plurality of wavelengths of amplified spontaneous emission light produced in the amplification medium.

Abstract: A transmission apparatus designed to be capable of monitoring faults which occur between the input stage of an optical multiplexer and the input stage of an optical amplifier, appropriately switching between automatic gain control and automatic level control, and outputting signal lights with appropriate optical power, without using a spectrum analyzer. The optical multiplexer combines the wavelengths of a plurality of signal lights. The optical amplifier is connected at the latter stage of the optical multiplexer, and operates in the automatic gain control mode or in the automatic level control mode, the automatic gain control mode maintaining a constant gain for wavelength-multiplexed signal light, the automatic level control mode maintaining constant output power for the wavelength-multiplexed signal light.

Abstract: A pumping unit supplies pumping light to a fiber connecting medium; a light monitoring unit detects light power of multiple-wavelength light; and a control unit controls the pumping light based on light power detected by the light monitoring unit and connecting medium information indicating optical characteristics in the connecting medium. The connecting medium information includes information indicating a fiber type of the fiber connecting medium, information indicating a length of the fiber connecting medium, an average fiber loss coefficient of the fiber connecting medium and an intra-station loss value.

Abstract: An optical amplifier includes a rare-earth doped optical fiber or rare-earth doped optical waveguide serving as an amplification medium where rare-earth ions have been doped in its core and/or clad, an excitation mechanism for exciting the amplification medium, an optical resonator that causes laser oscillation at one or more wavelength of spontaneous emission light produced and amplified in the amplification medium, a monitoring mechanism that monitors a power of at least one light selected from a power of at least one light with at least one prescribed wavelength band selected from the light inputted to the amplification medium and a power of at least one light selected from a power of at least one light with at least one prescribed wavelength band selected from the light outputted from the amplification medium, and a control unit that controls the excitation mechanism based on a value from monitoring mechanism.

Abstract: An optical amplifying device includes an amplifying unit for amplifying an optical signal using stimulated emission; a filter unit for attenuating at least part of a band of an output of the amplifying unit other than a main signal band of the optical signal; and an amplification control unit for controlling the amplifying unit on the basis of an output of the filter unit, the amplification control unit having, as a mode for controlling the amplifying unit, an amplified spontaneous emission output mode for causing the amplifying unit to operate, with the optical signal not being input to the amplifying unit, and for causing the filter unit to filter the amplified spontaneous emission output from the amplifying unit and to output the filtered amplified spontaneous emission to outside.

Abstract: There is described a method for compensation of gain variations in a multistage optical amplifier, for the amplification of an optical wavelength multiplex signal, comprising several amplifier stages in series, each with at least one pumping device. Gain variation occurring after a switching process can easily be compensated for, when the power jump expected at the second amplifier stage is determined and, depending thereon, a new pump power is calculated for the corresponding pump device, the new pump power is set for the pump device before the power jump arrives at the input of the second stage.

Abstract: Provided is an all-optical gain-clamped fiber amplifier, comprising transmission and isolation means for periodically transmitting an optical signal or reflecting amplified spontaneous emission (ASE) back to a gain medium. The transmission and isolation means can be embodied by an optical interleaver or a number of optical fiber Bragg gratings. Accordingly, an optical signal can be amplified across the entire C-band, and an ASE reflector-based gain-clamped fiber amplifier having a wider dynamic range than conventional amplifiers can be implemented.

Abstract: A proportional constant adjusting circuit is arranged in the AGC circuit of the optical amplifying apparatus, and the proportional constant of the proportional circuit is continuously adjusted in correspondence to the optical input power monitored by the PD and the logarithmic transformation circuit. The AGC circuit controls the pump LD based on the monitored optical input/output power so as to control the gain of the optical amplifier to be a requested value.

Abstract: Optical amplifier transient control methods and apparatus which limit the extent of cumulative transient gain errors in the rapid control of multiple optical amplifiers in a communication system. In an exemplary embodiment, if the input power to an optical amplifier drops below a predetermined threshold, the gain of the amplifier is set to clamp the output power of the amplifier to its initial level less the threshold, thereby preventing the continuous growth of gain error. This is based on the assumption that once the input power goes below the threshold, it should no longer go above the threshold until the transient condition is corrected. The present invention can operate to handle down- as well as up-transient events and is not amplifier technology dependent.

Abstract: An optical amplifier is disclosed that includes an input monitoring part configured to monitor an input wavelength division multiplexed light; an amplification part configured to amplify and output the input wavelength division multiplexed light; an output monitoring part configured to monitor the wavelength division multiplexed light output from the amplification part; a gain control part configured to perform gain control so that the ratio of output light intensity monitored by the output monitoring part to input light intensity monitored by the input monitoring part is constant; and a response speed switching part configured to switch the response speed of the gain control.