Abstract: The present invention relates to a wavelength-multiplexed light amplifying apparatus to be used in a state of being connected to a branching portion of a multiplexing/branching unit or to be used for a m×n matrix optical switch of an optical cross-connect. The wavelength-multiplexed light amplifying apparatus is composed of a plurality of wavelength-multiplexed light amplifying units and an optical feedback loop system. A signal input port of an optical branching section in one wavelength-multiplexed light amplifying unit is connected to an output side of an optical amplifying section in the preceding wavelength-multiplexed light amplifying unit. This configuration disperses the power loss of an optical signal to perform amplification with high efficiency and further enables the expansion of the branching port in the in-service.

Abstract: An optical brancher 110 branches an input optical signal into two. An optical detector 120 converts one optical signal branched by the optical brancher 110 into an electrical signal. A first controller 122 generates a control electrical signal having a waveform obtained by inverting the envelope of the electrical signal. Based on the control electrical signal, an optical signal generator 124 produces a dummy optical signal having a waveform &lgr;d and an amplitude &agr;/2. The other signal branched by the optical brancher 110 is delayed by a delay unit 112 for a predetermined time, and then multiplexed by an optical multiplexer 114 with the dummy optical signal from the optical signal generator 124. An optical amplifier 116 amplifies a multiplexed optical signal. An optical filter 118 separates an optical signal of a wavelength &lgr;1 from the amplified optical signal. Thus, optical signal amplification can be carried out without optical surges.

Abstract: The first present invention provides an optical switch including the following elements. At least a plurality of optical transmission lines are provided for transmissions of optical signals. Each of the at least plurality of optical transmission lines have a least an impurity doped fiber. At least an excitation light source is provided for emitting an excitation light.

Abstract: The present invention is to provide an optical fiber amplifier for clamping and equalizing gain in optical communication systems comprising: a gain clamping amplifier unit for clamping the gain, so as to make input signals have the same output power for each channel by applying a compensating signal; a second isolator for passing the input signal light from said gain clamping amplifier unit and isolating the light coming from the opposite direction; a gain equalizing filter for equalizing the output gain spectrum from the input signal from said second isolator; and a post-amplifier unit for amplifying the signal from said gain equalizing filter. Thus, the optical fiber amplifier is capable of clamping gain automatically by maintaining the same population inversion, and capable of maintaining the same gain equalization for the wide signal gain band to achieve the high transmission capacity, in cases that the number of channel varies in the input signal, while providing a high output signal power.

Abstract: An optical equalizer for use primarily with an erbium-doped fiber amplifier has an initial polarizer that convert the input beam to a predetermined polarization, followed by a series of dynamically-adjustable sinusoidal filters that provide attenuation as a sinusoidal function of beam wavelength. Each of the sinusoidal filters has a first liquid crystal cell adjustably rotating the polarization of the beam from the preceding polarizer. This is followed by a second optical element that retards the beam as a sinusoidal function of beam wavelength. For example, the second optical element can be a birefringent crystal that provided a fixed degree of retardance to the beam and a second liquid crystal cell that provides a variable degree of retardance, thereby allowing adjustment of the center frequency of the sinusoidal function. Finally, a third liquid crystal cell adjustably rotates the polarization of the beam.

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: Multiple function bandwidth management systems. Bandwidth-management systems for an optical network are easily assembled by concatenating a plurality of intelligent, miniaturized, bandwidth-management modules (BMM's) together. The BMM's subdivide the wide available spectrum into narrow band segments. Each individual BMM is designed to overcome loss and optimize dispersion, gain, and power or gain equalization for a few channels at a time. Each device includes optical connectors and filters, as well as any other components necessary to direct the band of optical channels through the device's optical path while passing other optical channels within the spectrum to additional devices which can be connected without disturbing existing bandwidth-management modules. Each BMM also includes a digital control module that operates the BMM in any one of a plurality of selectable operating modes.

Abstract: The present invention provides a wavelength division multiplexed optical communication system including an optical fiber ring configured to carry at least one wavelength division multiplexed optical communication signal having plural optical channels at different wavelengths. Optical amplifiers are interposed along the optical fiber ring for optically amplifying the wavelength division multiplexed optical communication signal. Each optical amplifier produces amplified spontaneous emission as well as amplifying the optical channels of the WDM signal. At each amplifier, amplified spontaneous emission is selected by an optical feedback selector and is fed back to the optical amplifier input via an optical feedback path; the created wavelength travels along the ring and is dropped near the input of the next adjacent amplifier, reducing ASE in the optical fiber ring.

Abstract: In a light unit that converts a false linear light into which a light from a point light source has been converted by a columnar light guide, into a planar light by a plate-shaped light guide, the point light source is arranged only at an end of the columnar light guide at which an angle between a longitudinal direction of the columnar light guide and ridge lines of recesses and projections forming a prism surface is obtuse. Thus, a positional relationship between the point light source and the ridge lines is set so that a main irradiation direction of band-shaped light emitted from the columnar light guide and which has been obtained by converting the light from the point light source to a false linear light is not substantially orthogonal to the ridge lines of the recesses and projections forming the prism surface of the plate-shaped light guide. Consequently, light obtained by totally reflecting this band-shaped light is unlikely to be viewed.

Abstract: Disclosed is an optical amplifier, comprising: at least one optically amplifying unit having: a forward excitation light source for generating a forward excitation light; a forward excitation light coupler for coupling the forward excitation light with an input optical signal; an optically amplifying medium for amplifying the input optical signal combined with the forward excitation light; a backward excitation light source for generating a backward excitation light; a backward excitation light coupler for coupling the backward excitation light with the amplified optical signal; a first controller for controlling the forward excitation light source to generate the forward excitation light with a power up to a maximum power thereof; and a second controller for controlling the backward excitation light source to generate the backward excitation light in such a way that the backward excitation light compensates gain deficiency as compared with a desired gain of the optical amplifier.

Abstract: In a light amplifier and a light amplifying method, a dummy light (saturated light) source 40 emits dummy light, a directional coupler 11 composes the dummy light with a light signal, and the composite light of the light signal and the dummy light is split into two parts to output a part thereof to a directional coupler 12. One part of the composite light (the light signal and the dummy light) output from the directional coupler 12 is amplified by a light amplifying portion 20, and the dummy light is removed from the composite light thus amplified by a dummy light removing filter 31. A dummy light (saturated light) source control circuit 50 controls the dummy light source 40 so that the light output of the dummy light source 40 is equal to predetermined light output. With this construction, lack of light input power due to reduction in the number of channels of the light signal of a transmission path is compensated by dummy light, thereby preventing over power of the signal light of the remaining wavelength.

Abstract: An optical amplifying apparatus for widening the input dynamic range and lowering noises. The optical amplifying apparatus comprises a first optical amplifier, an optical attenuator, a second optical amplifier and a controller. The first optical amplifier changes the target value of output light when the variance amount of input light reaches a predetermined value. The controller changes the attenuation amount of attenuator in accordance with a difference between the target value and the changed target value of the output light level of the first optical amplifier, when the target value of the output light level of the first optical amplifier is changed.

Abstract: The dual wavelength pumping scheme controls the relative population of the termination state vis-a-vis the metastable state. Praseodymium doped chalcogenide glass and a variety of thulium doped glasses are described as examples. The relative pump powers or wavelengths may be adjusted to control the gain spectrum of the amplifier, making the amplifier useful in a variety of different optical systems including wavelength division multiplexed systems.

Abstract: The present invention relates to an optical attenuator comprising first and second attenuator units cascaded on an optical path, and a control circuit connected to the first and second attenuator units. Each of the first and second attenuator units includes a Faraday rotator provided on the optical path. The Faraday rotator generates a Faraday rotation angle given as a function of wavelength. Each of the first and second attenuator units further includes polarizing unit for generating an attenuation determined by the Faraday rotation angle on the optical path. The control circuit, for example, controls the Faraday rotation angle in each of the first and second attenuator units so that a wavelength characteristic of attenuation in the first attenuator unit is substantially canceled by a wavelength characteristic of attenuation in the second attenuator unit.

Abstract: A broadband nonlinear polarization amplifier includes an input port for inputting an optical signal having a wavelength &lgr;. A distributed gain medium receives and amplifiers the optical signal through nonlinear polarization. The distributed gain medium has zero-dispersion at wavelength &lgr;0. A magnitude of dispersion at &lgr; is less than 50 ps/nm-km. One or more semiconductor lasers are operated at wavelengths &lgr;p for generating a pump light to pump the distributed gain medium. An output port outputs the amplified optical signal.

Abstract: An optical transmission unit is comprised of an optical power control unit to adjust the optical power, an optical detection unit to detect the power of the optical signal from a transmission medium, an optical control-information generating unit to generate information relating to the size of the detected optical power monitor value, an optical control-information introduction unit to input the generated information into the transmission medium as optical control information, an optical control-information input detection unit to detect optical control information from the transmission medium, and a control unit to regulate the detected information so the optical power from the optical power adjustment device is within a specified value.

Abstract: Disclosed is an optical signal repeating and amplifying device which has: an optical amplifier which amplifies an optical signal to be input thereto and then outputs it; and an optical filter means through which only one wavelength light of the optical signal to be output from the optical amplifier is passed. Also disclosed is an optical level adjusting device which has: an optical demultiplexer which demultiplexes a wavelength-multiplexed optical signal into a plurality of wavelength lights; a plurality of optical attenuators which attenuate separately the demultiplexed plurality of wavelength lights to be output from the optical demultiplexer; and an optical multiplexer which multiplexes the attenuated wavelength lights to be output from the plurality of optical attenuators into a wavelength-multiplexed optical signal and output it.

Abstract: Disclosed herein is an inhomogeneity tunable erbium-doped optical fiber amplifier with a long wavelength band and method of blocking a backward amplified spontaneous light emission in the same. The optical fiber amplifier includes a control device situated between a first amplification stage and a second amplification stage for controlling an isolation rate of a backward amplified spontaneous light emission being propagated from a second amplification stage to the first amplification stage. The method blocks a backward amplified spontaneous light emission in a two-stage inhomogeneity tunable erbium-doped optical fiber amplifier with a long wavelength gain band, in which the backward amplified spontaneous light emission being propagated from a second amplification stage to a first amplification stage is blocked, and an isolation rate of the backward amplified spontaneous light emission is controlled according to the intensity of an optical signal inputted to the first amplification stage.

Abstract: The invention refers to an optical power equalizer. Known devices receive an optical main input signal modulating between high and low input power levels. They emit an equalized optical main output signal modulating between high and low output power levels, where at least one of the two sets of high and low power levels is equalized to one high or one low output power level. Such devices can comprise at least one gain-clamped semiconductor optical amplifier, adjusted to work about its saturation range, receiving an amplifier input signal, consisting of one or more portions of which at least one is modulated and emitting a modulated amplifier output signal. According to the invention the dependence of the GC-SOA's gain on the power of the amplifier input signal is adjusted in such a way, that the high input power levels of said amplifier input signal are directly converted into the one high output power level of said amplifier output signal.

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 &Dgr;, the controller controls a level of the light received by the second optical amplifier to change by approximately −&Dgr;. 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: A bi-directional optical amplifier arrangement for use in an optical path along which a bi-directional optical signal is travelling, the arrangement comprising at least two amplifier units disposed to amplify, in use, in different propagation directions, at least two propagation direction dependent optical junction elements, at least two optical paths disposed in parallel between the junction elements, wherein each optical paths comprises one of the amplifier units; and wherein gain settings of the amplifier units are chosen in a manner such that, in use, a total gain experienced by an optical signal re-circulating along both optical paths is less than unity.

Abstract: Feedback instabilities arising from interactions between automatic control loops at the amplifier nodes of an optical network are eliminated by restricting operation to a single amplifier node at a time. Amplifier node activation is accomplished using a global control signal which is sequentially passed from an upstream node through all of the nodes of the system. By controlling the state of the global control signal, an upstream node has operational priority over downstream nodes.

Abstract: The present invention improves the performance of optical networks, particularly optical ring networks, by reducing amplified spontaneous emission thereby increasing the available gain of optical amplifiers within that network. In one embodiment, the invention provides a WDM optical communication system having an optical fiber ring with optical fiber amplifiers interposed along the ring. An optical wavelength is injected into the optical fiber ring at a first location; the optical wavelength is selected to be located within a region of amplified spontaneous emission for the optical fiber amplifier. The optical wavelength is dropped from the optical fiber ring at a second location positioned such that the injected optical wavelength is dropped at or prior to returning to the first location within the ring. The optical wavelength passes through at least two of the plurality of optical amplifiers before being dropped from the optical fiber ring.

Abstract: A fiber Raman amplifier is configured to use a co-propagating Raman pump source, which may be beneficial in a variety of system configurations (for example, in bidirectional communication systems). By carefully configuring the pump source characteristics, sufficient optical gain can be achieved in the co-propagating arrangement, the characteristics including: (1) using an optical pump power of at least 50 mW, (2) having a relatively large spectral bandwidth within the pump (to suppress SBS); and (3) a frequency difference between all longitudinal pump modes of each pump laser being separated by at least the walk-off frequency between the pump laser frequency and the signal frequency, and all intense longitudinal modes between different pump lasers being separated by at least the electrical bandwidth of the communication system.

Abstract: An optical amplifier comprises: a first gain medium having an optical host that contains a rare earth dopant and a first pump that supplies optical energy at a first wavelength into this first gain medium. The first gain medium is an optical fiber of a predetermined length, such that inversion of this first gain medium is not saturated. The optical amplifier further comprises a second gain medium operatively coupled to the first gain medium and a second pump that supplies optical energy into the second gain medium. According to an embodiment of the present invention the predetermined length of the optical fiber of the first gain medium is 1 to 6 meters and preferably 1.5 to 4.5 meters.

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: WDM transmission system comprising transmitters 2 for generating optical signals in different channels, a multiplexer 3 for combining said optical signals into a WDM signals, a transmission line 4 for transmitting said WDM signal, a demultiplexer 6 for demultiplexing the WDM signal received from the transmission line 4 and receivers 7 for receiving the optical signals of each channel, characterized in that it further comprises a Raman depletion compensator 8, 10 for compensating the depletion due to Raman-shift in the power of the wavelength grid spectrum.

Abstract: A method of providing a predetermined insertion loss in an optical fiber amplifier,includes the step of utilizing a predetermined, fixed, spectrally-flat loss compound (insertion loss pad, ILP) to pad total optical fiber amplifier insertion loss up to a predetermined fixed level.

Abstract: Data transmitted on optical fiber over long distances is subject to the introduction of errors at the receiving end, caused by distortions and alterations of the original data. Raising the transmission power to increase the level of signals at the receiving end also increases errors due to non-linear characteristics of the fiber. The invention optimizes launch power by assessing error rates due to amplified spontaneous emissions and due to four wave mixing, so that signal to noise ratios due to these causes exceed threshold levels while enabling launch power to be maximized.

Abstract: An optical amplifier and optical amplifier arrangement with reduced cross phase modulation wherein in an active fiber of the optical amplifier, the fiber being doped with ions of elements from the group of rare earths, in order to reduce the cross phase modulation of the optical amplifier, at least one active fiber section is allocated a dispersion coefficient having a high magnitude, in which the optical transmission signal to be amplified assumes a high signal level.

Abstract: An apparatus for maintaining the temperature stability of an amplifier system comprises a device for heating, cooling or heating an cooling one or more sub-assemblies of the amplifier system, a temperature sensor for detecting variations in temperature of a sub-assembly, and a controller operably connecting the two. The signal from the sensor is used by the controller to adjust the amount of heating, cooling, or heating and cooling of a sub-assembly in order to maintain its temperature within a range sufficiently small to ensure stable performance.

Abstract: The cross phase modulation generated by a fiber amplifier is compensated for by converting the amplitude variations of the wavelength-division multiplex signal (WMS) into an electrical signal which controls a phase modulator (2) in such a manner that the signal distortion caused by cross phase modulation is compensated for.

Abstract: An optical amplifying apparatus of the present invention comprises a correction part for correcting a predetermined fixed value of an output optical level by a correction amount according to an optical power of amplified spontaneous emission (ASE). The correction amount is, for example, computed by predetermined formulas. According to the present invention, when a WDM optical signal is optically amplified, the output is fixedly amplified for each channel by the correction amount which is a value obtained with the ASE levels taken into consideration, so that a fluctuation in the level of the average optical power of the channels is suppressed even if an optical signal is dropped/added therefrom/thereto during repeated transmissions.

Abstract: An optical amplifier comprises a pumped doped fiber with a power measurement circuit for measuring the input and output power of the amplifier. Automatic gain control is implemented, and the calculation of output power for the AGC loop takes into consideration the temperature provided by a temperature measurement device. This enables a flatter gain response to be achieved over varying input power, which enables an increase in the dynamic range of the amplifier and thereby a possible increase in system capacity of a WDM system using the amplifier.

Abstract: In an optically amplified wavelength division multiplexed (WDM) system having a WDM signal comprising a plurality of optical channels, the per-channel gain of the optical channels is kept relatively constant despite changes in input power at the optical amplifier, such as when individual optical channels of the WDM signal are added and dropped. More specifically, gain of an optical amplifier is controlled by controlling the amount of pump power supplied to the optical amplifier as a function of changes in input power which are measured in a feed-forward monitoring path. The amount of pump power for effecting gain control is adjusted according to a scaled relationship to the measured input power of the optical amplifier. By controlling the pump power directly in response to changes in input power, gain of the optical amplifier can be controlled within a sub-microsecond time scale from the time that a change in input power is detected.

Abstract: An optical amplifier has a gain profile which is substantially flat and independent, over a wide range, of the pump power, power of the input signals, and the number of input signals. The amplifier utilizes an optical resonator having a gain medium whose gain broadening behaves inhomogeneously by pumping the gain medium at at least one wavelength in at least one absorption tail of the gain medium. The resonator is a ring resonator that preferably includes an erbium-doped fiber. Codopants may be added to the fiber to enhance the inhomogeneous broadening effect. A method of gain flattening introduces a pump signal into a gain medium. The pump signal has a wavelength in the tail of the absorption profile of the gain medium. A plurality of optical signals at different wavelengths are introduced into the gain medium. Stimulated emission within the gain medium clamps the gain of the gain medium.

Abstract: An apparatus and method are described for controlling response to power transients in an optically amplified wavelength division multiplexed (WDM) network when WDM optical channels are added and dropped, during network reconfigurations, during failure events, and so on. In one embodiment, a variable bandwidth filter circuit operates at a first prescribed bandwidth during a first time period &tgr;0 to detect a change in signal power (i.e., power transient) caused by a transient event, and operates at a second prescribed bandwidth that is less than the first prescribed bandwidth after the first period of time elapses, e.g., &tgr;0+&Dgr;&tgr;, to substantially suppress low level signal variations, such as remnants of the power transient. In this way, the power transient related to the actual transient event will be preserved to trigger control circuitry, e.g.

Abstract: An optical level controller (13) for a wavelength division multiplex optical communication network (17) includes one or more variable gain elements (1;9) adapted to suppress transient amplitude fluctuations in traffic signals caused by the adding or the dropping of traffic signals at one more points in the optical communication network. The at least one variable gain element (1;9) is controlled through a negative feedback loop adapted such that a response time of the negative feedback is shorter than a time scale of the transient amplitude fluctuations.

Abstract: A wavelength division multiplexed transmission system and a transmitting method using the same are provided. The wavelength division multiplexed transmission system includes a transmitting optical terminal station for transmitting a supervision channel, delaying a plurality of data channels by a predetermined time, and transmitting the delayed data channels, a plurality of wavelength division multiplexed optical amplifying portions for controlling amplification gain according to gain information included in the supervision channel and amplifying the delayed and incident data channels according to the controlled gain, and a receiving optical terminal station for receiving the supervision channel and the data channels output from the wavelength division multiplexed optical amplifying portion.

Abstract: The method and system are disclosed for reducing an optical surge in an optical data communication system that includes at least pair of optical lines, optical switches and optical amplifiers to maintain high reliability in data transmission. The optical surge is substantially reduced or suppressed by assuring a proper timing of the optical switch operation based upon a predetermined elapsed time or a predetermined safe amplification gain of the optical amplifier.

Abstract: Compound gain flattening filters of optical amplification include a series of filter components with spectral responses that are combined to approach a target loss spectrum. Small variations in the central wavelengths of the component responses can produce large errors in the combined response of the compound gain flattening filter. However, the components can be divided into sub-components with balanced central wavelength deviations to achieve the desired response goals despite exhibiting otherwise detrimental wavelength deviations.

Abstract: An all fiber optical filter is formed by stretching an optical fiber. The all fiber filter includes a core, an inner cladding, and an outer cladding. A core index of refraction is greater than an outer cladding index of refraction. The outer cladding index of refraction is greater than an inner cladding index of refraction. The all fiber optical filter attenuates a portion of an optical signal by transferring optical energy from the core to the outer cladding by evanescent coupling. The all fiber optical filter has a compact structure, which prevents bending and provides stable temperature performance. The all fiber optical filter is preferably used in Wavelength Division Multiplexing (WDM) systems for gain flattening of gain responses from Erbium Doped Fiber Amplifiers (EDFAs). Alternatively, the all fiber optical filter is used in other applications where optical filtering or attenuation is needed.

Abstract: A double cladding fiber and an optical fiber amplifier, which have a function equivalent to that of a pumping light cut filter with a simple structure are provided. In the double cladding fiber, a core transmitting a signal light is covered with a first clad having a refractive index of n7b. A second clad having a refractive index of n7c, covers the surrounding surface of the first clad. At an output end of the fiber, a designated length of the second clad is removed and a substance having a refractive index of “n” (“n”>n7b) is coated on the first clad where the second clad has been removed. With this structure, a remaining pumping light leaks to this coated part. That is, and the substance coated part works as a filter for the remaining pumping light. As a result, a signal to noise ratio (SNR) of the amplified signal light is improved with a simple structure.

Abstract: A pump light source provides pump light to an optical fiber arranged to guide the pump light to a first optical isolation device. Light output by the first optical isolation device is input to a wavelength division multiplexer. A gain fiber is connected to the wavelength division multiplexer and arranged to be optically pumped by the pump light such that the gain fiber emits broadband light that propagates to the wavelength division multiplexer. An output optical fiber is connected to the wavelength division multiplexer and arranged to guide a portion of the broadband light emitted by the gain fiber to a second optical isolation device for input to a fiber optic rotation sensor.

Abstract: An optical isolator module in which an optical splitter for splitting an optical signal input through an input port, an optical detector for detecting the separated light, and a compensator for compensating for polarization mode dispersion are integrated into a single component along with an isolator, and an optical amplifier employing the optical isolator module are disclosed. In the optical isolator module, a first lens focuses the incident optical signal. A first birefringent device has a tapered shape in which a first incident surface forms a first predetermined angle with a first emitting surface from which a polarized light is emitted, and the incident surface of the first birefringent device is coated for partial reflection so that the portion of the incident optical signal is reflected as an reflected light. A Faraday rotator rotates polarized light by a second predetermined angle.

Abstract: In an optical amplifier evaluation instrument, a rectangular spectrum light source 1 transmits continuous light having a wide-band and flat spectrum shape, a first optical modulator 2 receives and pulse-modulates the continuous light. Further, a second optical modulator 3 operates in the same period as the first optical modulator 2 and performs the on/off pulse operation, thereby providing a sampling window in a time domain for extracting and suppressing an optical signal. A modulation signal generation section 4 performs such control and drive. An optical signal undergoing pulse intensity modulation is input to a measured optical amplifier 6. Post-amplified signal light power for each frequency component and amplified spontaneous emission power for each frequency component in a time domain in which no optical pulse signal exists are measured and operations are performed for each wavelength.

Abstract: In an optical communication system, the signal power level injected into each of one or more optical fiber spans is reduced so as to suppress undesired non-linear effects. This reduction in injected signal level is made possible by remotely pumped amplification in the spans that are affected.

Abstract: Techniques for controlling the shape of the gain spectrum of an optical amplifier (13) based on the temperature and level of inversion of the amplifier's amplifying medium (20) are provided. An increase in temperature for an amplifying medium having a high level of inversion results in an increase in gain for longer wavelengths relative to shorter wavelengths, i.e., a counterclockwise tilt of the gain spectrum, while an increase in temperature for an amplifying medium having a lower level of inversion results in the opposite effect, i.e., a clockwise tilt. These effects can be used to compensate for changes in the operating conditions of the amplifier, e.g., to compensate for changes in signal powers. The effects of thermal tuning are especially useful in WDM systems employing multi-stage amplifiers.

Abstract: Each of a series of optical amplifiers is arranged such that, in response to detecting particular stimuli occurring at an input or receipt of an adjustment start message from an upstream amplifier, adjusts certain amplifier parameters using small steps and completes the adjustment using large steps if it does not receive the adjustment start message within a predetermined period of time of starting the adjustment in response to detecting the stimuli. If the optical amplifier receives the adjustment start message, then it continues to perform the adjustment and completes the adjustment using large steps when it receives an adjustment done message from the upstream optical amplifier. At that point, the optical amplifier sends an adjustment done message to the next downstream amplifier if it is not the tail-end amplifier.

Abstract: An optical amplifier that can easily cope with alteration of characteristics and whereby a prescribed characteristic can be obtained in a stable fashion. In an optical amplifier, a plurality of optical components including optical amplification media that amplify input signal light are cascade-connected. There are provided (1) a temperature adjustment member capable of changing the temperature of one or a plurality of optical components in accordance with a temperature control signal that is input, and (2) a characteristic control device that supplies in respect of the temperature adjustment member a control signal that controls a prescribed optical characteristic having temperature dependence in one or a plurality of optical components that are the subject of adjustment by the temperature adjustment member, being a prescribed optical characteristic that is demanded for the optical amplifier.