Abstract: An optical device including an optical amplifier to amplify optical signals received through an optical input, and to supply the amplified optical signals from an optical output, and an optical filter coupled to the optical amplifier. The optical filter changes the gain slope of the optical amplifier in response to a change in a single parameter of the optical filter. The single parameter may be a change in a central wavelength of the optical filter function. The optical filter preferably has a parabolic spectral function. The single parameter may be varied as a function of temperature such that the variable optical attenuator compensates for variations in the gain spectrum of the optical amplifier that occur as a function of operating temperature.

Abstract: An apparatus for sensing changes, e.g. transient changes in the input or output signal spectrum of an optical amplifier, typically an EDFA, uses only a pair of spectrally banded photodiodes to equalize the transient behaviour of the amplifier. The photodiodes provide a control signal which is either sum or difference of signals generated by the photodiodes, that is used in the control of the optical amplifier in a feedback or feed-forward mode in order to counterbalance the effects of changes in the spectral content of the input (or output) signal of the optical amplifier.

Abstract: An optical transmission system for wavelength-division multiplex signals, having cascaded Raman amplifiers, has a number of pump sources for each Raman amplifier, each having different pump wavelengths sets from one pump source to another pump source. This results in a flat gain spectrum for all the channels in a WDM transmission signal.

Abstract: An optical amplifier and communications system for amplifying an input signal and providing an output signal includes a nonlinear light absorber for passively controlling the level of the output signal. The nonlinear light absorber provides an approximately constant output signal level independent of the level of the input signal.

Abstract: Disclosed is an optical gain equalizer for equalizing optical powers for a plurality of signal lights having wavelength different from one another. Disclosed are also an optical transmission line and an optical wavelength multiplex transmission system, for which the optical gain equalizer is used. The optical gain equalizer has a characteristic where a loss is monotonously changed in a signal wavelength band. A characteristic of a monotonous reduction of loss from a short wavelength to a long wavelength and/or a characteristic of a monotonous increase of loss from a short wavelength to a long wavelength is utilized. Specifically, the optical gain equalizer is composed of a well-known optical element such as an optical etalon filter, an optical band-pass filter, an optical fiber grating or the like. Even if a loss varies on the optical transmission line, the optical gain equalizer can provide an uniform optical power for respective channels.

Abstract: An optical device including an optical amplifier to amplify optical signals received through an optical input, and to supply the amplified optical signals from an optical output, and an optical filter component to compensate for variations in the gain spectrum of the optical amplifier that occur as a function of wavelength and operating temperature. The optical filter component includes a first optical filter having an athermalized transmission spectrum and a second optical filter having a transmission (or insertion loss) spectrum that varies as a function of operating temperature.

Abstract: A method for controlling the shape and magnitude of the L-band gain spectrum of an erbium doped optical amplifier, in one aspect, involves saturating the amplifier gain with a saturating signal in the L-band. Another aspect of the method involves saturating the amplifier gain by controlling the temperature of the gain medium. By pumping the amplifier in the 980 nm and/or the 1480 nm pump bands, the gain spectra at different inversion levels are adjusted.

Abstract: An optical signal amplification device (200) comprises an optical amplifier (210) having a wavelength-dependent gain and an equalization device (100) optically coupled in series to the optical amplifier and having a wavelength-dependent transmission function that substantially equalize the gain of the optical amplifier, the equalization device comprising a waveguide Bragg grating having a substantially constant refractive index envelope and a chirp rate that varies in such a way as to obtain the wavelength-dependent transmission function.

Abstract: An optical gain flattening filter for attenuating the wavelength power levels of an optical beam to a threshold value. The filter has a series of volume phase gratings which each have a loss spectrum. The sum of the loss spectra for the volume phase gratings is about equal to the opposite of the gain spectrum of the optical amplifier. As the optical beam passes through the volume phase gratings, the sum of the loss spectra is added to the gain spectrum of the optical amplifier such that the optical beam is attenuated to the threshold value.

Abstract: A wideband optical amplifier for amplifying an input optical signal of known wavelength in one of at least two bands of wavelength has a significantly small number of optical components and thus is low cost. The wideband optical amplifier includes: a first set of a first optical coupler, a first pump light source, and a first erbium doped optical fiber (EDF) which is excited by the first pump light source; an optical switch for changing an output signal of the first set; and a second set of a second optical coupler, a second pump light source, and a second EDF which is excited by the second pump light source. The first set amplifies a first band of optical signal while a series connection of the first set and the second set amplifies a second band of optical signal. In another aspect, a wideband variable wavelength optical source is achieved by utilizing the wideband optical amplifier described above within a closed loop.

Abstract: A dynamic controller for a multi-channel EDFA-type optical amplifier is provided that is capable of providing a substantially tilt-free output over a range of selectable gain set points. The dynamic controller includes a variable optical attenuator coupled between the two amplification coils of the EDFA amplifier, and a control circuit that instructs the attenuator of an amount that each channel should be attenuated to achieve a tilt-free output at a selected gain point. The controller further includes a gain controller and a tilt controller connected to the control circuit of the variable optical attenuator for providing signals indicative of an average amount of per channel attenuation and a relative amount of per channel attenuation necessary to achieve a selected gain set point while reducing or eliminating tilt, respectively.

Abstract: Disclosed herein is a method for level equalization. In this method, a first optical amplifier having a gain tilt coefficient defined as a change in gain tilt to a unit change in gain is first provided. A second optical amplifier having a gain tilt coefficient different from the gain tilt coefficient of the first optical amplifier is cascaded to the first optical amplifier. The gains of the first and second optical amplifiers are distributed so that a level tilt of light amplified by the first and second optical amplifiers becomes substantially flat. Thus, it is possible to provide a simple method for allowing automatic level equalization by providing a plurality of optical amplifiers having different gain tilt coefficients and distributing the gains of these optical amplifiers so that a level tilt of light amplified by these optical amplifiers becomes substantially flat.

Abstract: A bidirectional add/drop optical amplifier used in wavelength division multiplexing (WDM) optical networks to suppress the power change resulting from the adding and dropping of optical signals using an all optical gain control includes two fiber Bragg gratings (FBGs) and a bidirectional add/drop optical amplifier module composed of an Arrayed Waveguide Grating (AWG) and two bidirectional optical amplifiers. The filtered amplified spontaneous emission (ASE) lights are lased with the two FBGs and then used to adjust the gain of the bidirectional amplifiers.

Abstract: An optical amplifier has at least first stage in the form of a distributed Raman amplifier and a second stage in the form of a discrete Raman amplifier. The discrete amplifier has an output for unused pump power, and the distributed Raman amplifier is pumped using the unused pump power from the second stage. This arrangement enables unused pump power to be used in a distributed Raman amplifier, in particular using the transmission fiber at the input to the second stage amplifier.

Abstract: A method and apparatus for dynamically obtaining a substantially linear gain tilting of the output spectrum of an EDFA, in either automatic gain control or automatic power control modes. A necessary tilt is obtained while holding the total gain or total output power of the EDFA constant. The apparatus includes a variable mid-stage attenuator inserted between two (first and second) gain sections of the EDFA. The tilting is performed by ordering the attenuator to increase or decrease its attenuation in a value proportional to the tilting needed, while changing substantially simultaneously the pumping of the second gain section. The attenuation change process is based on the saturation mechanism of the erbium amplifier in the L-band, which translates the wavelength-independent loss of a variable optical attenuator into a linear wavelength-dependent gain at the EDFA output.

Abstract: Devices and methods for equalizing the gain of an optical amplifier are described. For devices including harmonic filters that are controllable by amplitude control voltages and phase control voltages, techniques for controlling the amplitude control voltages and phase control voltages are presented. Additionally, device architectures are described by which an incoming optical signal is equalized to compensate for uneven gain in prior amplifiers or other optical components, and in which the incoming optical signal is received at a beam displacer and separated into orthogonal component beams, wherein the beams are counter-propagated through the equalizer in opposite directions through the same spatial path so as to minimize or eliminate the effects spatially dependent imperfections in the equalizer.

Abstract: A variable gain optical amplifier, in which homogeneous gain broadening is dominant, has first and second fixed gain rare-earth doped optical waveguide amplifiers (21, 23) optically in series together with an intervening variable attenuation optical attenuator (22). This arrangement circumvents the problem of gain tilt encountered when operating such amplifiers under variable gain conditions. An alternative form of the module has variable gain waveguide amplifiers, but these are co-regulated so that the aggregate of their gain at a wavelength within the gain spectrum is maintained constant. A further alternative form of module is employed in a concatenation of such modules. In such a concatenation, the gain of individual modules is allowed to vary, but the aggregate of the gain, at a wavelength within the gain spectrum, of all the waveguide amplifiers of all the modules of the concatenation is maintained constant.

Abstract: This invention relates to invention relates to a method for filtering and a variable slope optical filter for in-line use with an optical amplifier signal. The filter has a wavelength response that is substantially linear in slope within a band of operation wavelengths of the amplifier; the slope of the filter in an operating band of wavelengths is between zero and a only one of a positive or negative number; furthermore the filter has an amplitude response that has an opposite and counter slope as a function of wavelength to that of a gain tilt of the amplifier within the operation band of wavelengths. Relative movement between the filter and the optical amplifier signal is provided to vary the slope of the filter by means of varying the amplitude wavelength response of the filter.

Abstract: A variable optical gain equalizer in accordance with one embodiment of the present invention comprises a variable branching ratio beam splitter having a variable polarization rotator, the variable branching ratio beam splitter branching an input light beam into two light beams at an arbitrary power ratio, through control of the rotation angle of the polarization direction by the variable polarization rotator; an optical filter presenting different filter characteristics to the two branched output light beams; and a polarization coupler for polarization coupling the two light beams that have passed through the optical filter, wherein the rotation angle of the polarization direction is controlled by the variable polarization rotator so as to vary the spectra of the output light beams.

Abstract: An optical amplifier of a wavelength-division multiplexing transmission system that includes a pre-stage optical amplifying unit and a post stage optical amplifying unit. The pre-stage optical amplifying unit has a rare-earth element doped optical fiber and a pump light source for inputting a pump light to the rare-earth element doped optical fiber. The post-stage optical amplifying unit has a second rare-earth element doped optical fiber and a pump light source for inputting a pump light to the second rare-earth element doped optical fiber. The pre-stage optical amplifying unit and the post-stage optical amplifying unit are optically connected by a detachable optical coupling device. In addition, a gain equalizing unit, positioned on an output side of the optical fibers, compensates for wavelength-dependency of a gain characteristic of the optical fibers.

Abstract: An optical amplifier waveguide provides variable amplification gain to a broad wavelength input signal. The degree of amplification is proportional to the length of the transmission of the input signal along the amplification waveguide. The amplification waveguide means further comprises a series of output wavelength couplers, which are preferably fiber gratings, placed along the length of the amplification waveguide for coupling a predetermined amplified signal from the amplification waveguide to the output fiber. Additionally, the optical amplifier waveguide of the present invention may include a plurality of noise wavelength coupling means, which are preferably fiber gratings, for coupling unwanted noise from the amplification waveguide means to a noise dissipation means.

Abstract: A compensation scheme for an optical amplifier that reduces differences in gain observed at various wavelengths combines and controls characteristics of an automatic gain control circuit and variable gain equalizers. The peak gain wavelength typically observed in optical amplifiers is reduced by shifting the variable gain equalizer characteristic, which has a wavelength region of maximum gain loss. By combining the characteristics of the peak wavelength gain with the maximum wavelength loss according to the various elements, a smooth gain curve can be realized. A variable gain equalizer control circuit provides the required control, and can control multiple variable gain equalizers positioned in various numbers and locations with regard to an optical amplifier section.

Abstract: A multi-mode gain fiber is provided which affords substantial improvements in the maximum pulse energy, peak power handling capabilities, average output power, and/or pumping efficiency of fiber amplifier and laser sources while maintaining good beam quality (comparable to that of a conventional single-mode fiber source). These benefits are realized by coiling the multimode gain fiber to induce significant bend loss for all but the lowest-order mode(s).

Abstract: An optical amplifier and communications system for amplifying an input signal and providing an output signal includes a nonlinear light absorber for passively controlling the level of the output signal. The nonlinear light absorber provides an approximately constant output signal level independent of the level of the input signal.

Abstract: An optical amplifier having a suitable length of Er/Yb co-doped double clad optical fiber is used to amplify an input optical signal. The inner clad of the double clad optical fiber supports the propagation of a multi mode signal used to excite Er/Yb co-dopants in the double clad optical fiber. Simultaneously, a single mode signal launched from a single mode laser pump co-propagates with the input optical signal in the core of the optical fiber. In this model, single mode light travels in the single mode core region and the multi mode pump light is mainly in the clad region. The interaction between the two laser pumps is negligible.

Abstract: An optical device including an optical amplifier to amplify optical signals received through an optical input, and to supply the amplified optical signals from an optical output, and an optical filter component to compensate for variations in the gain spectrum of the optical amplifier that occur as a function of wavelength and operating temperature. The optical filter component includes a first optical filter having an athermalized transmission spectrum and a second optical filter having a transmission (of insertion loss) spectrum that varies as a function of operating temperature.

Abstract: Spectral tilt controllers are provided for optical amplifiers and other optical network equipment used in fiber-optic communications links in fiber-optic networks. The tilt controllers may be used to adjust the gain or output power spectrum of an optical amplifier or to modify the optical data signal spectrum in other optical network equipment. Tilt controllers may use mechanical actuators to position a filter element substrate relative to an optical beam. Dielectric filters or other filter arrangements having various different spectral tilt characteristics may be implemented on the same substrate. Spectral tilt and average spectral attenuation values may be adjusted using the tilt controllers if desired.

Abstract: A method and apparatus for amplifying an optical signal is provided. In accordance with one example embodiment of the invention, the optical amplification system includes an optical signal traveling through the system. At least one module of the optical amplification system is suitable for one of selectively separating and combining one or more individual sub-bands of the optical signal. At least one amplifier is disposed to separately amplify each of the one or more individual sub-bands.

Abstract: An optical device comprises an optical amplifier to amplify optical signals, optical pumps coupled to and providing optical pump power to least one amplifying stage of the optical amplifier, so as to produce gain in the said optical amplifier and, a tunable optical filter coupled to the optical amplifier. The optical filter changes the gain slope of the optical amplifier in response to a change in a single parameter of the optical filter. The optical amplifier also includes at least one controller adjusting said single parameter of the optical filter and controlling the optical pumps.

Abstract: Disclosed is a gain equalizer which can adequately flatten the gain spectrum of an optical amplifier by reducing a deviation in center wavelength in accordance with a change in temperature, thereby improving the reproducibility and mass-productivity. The gain equalizer includes a minus filter. The minus filter includes a dielectric multilayer filter which has a transparent base having a first surface, a first dielectric thin film formed on the first surface and a second dielectric thin film formed on the first dielectric thin film. A difference between a refractive index of the first dielectric thin film and a refractive index of the second dielectric thin film is relatively small so that the minus filter has a reflection characteristic for reflecting an optical signal of a predetermined wavelength band including the peak wavelength of the gain spectrum.

Abstract: A switchable dynamic gain-flattened optical amplifier with wide adjustable gain range is provided. Optical signals are amplified through common amplification such that the gain is approximately common to all optical signals. Further, gain specific amplification is then achieved through distinct amplification wherein the optical signal is routed through one of N parallel amplification paths each having its well-designed gain. The amplifier makes use of a control circuit to self-adjust quickly and respond to changes in input conditions, operating conditions of the optical amplifier and gain requirements while maintaining gain flatness and a low noise figure (NF) over a broad optical bandwidth and a wide range of gain levels. The optical amplifier is highly desirable in dense wavelength-division-multiplexed (DWDM) systems for responding to changes in operating conditions due to link loss, pump deterioration, channel add/drop, and network reconfigurations.

Abstract: An apparatus and a method provide gain flattening in communications systems wherein a large number of optical signals at different wavelengths must be amplified while maintaining signal power within an acceptable range. Because of differences in gain of typical optical amplifiers as a function of wavelength and input power, the signals at different wavelengths are not amplified by the same amounts. Thus, when amplified multiple times, certain signals tend to become severely attenuated to the point of being no longer useable. The present gain flattening apparatus and method cause signals having higher gain-power products to be attenuated by a greater amount in response to Kerr-induced phase shifting such that after multiple stages of amplification, all the signal powers converge toward a small range of acceptable output powers.

Abstract: A signal light passes through an isolator, and is coupled by a coupler with a pump light from a pump light source. Then, the signal light passes through an ASE reflection filter, is amplified by an EDF, and is transmitted from an isolator. At this time, an ASE light having a predetermined wavelength among ASE lights that occur within the EDF and proceed to the ASE reflection filter is reflected and again input to the EDF. By setting the predetermined wavelength to a wavelength on the short wavelength side of an amplification band of the EDF, gain deviation occurring on the long wavelength side of the amplification band can be cancelled.

Abstract: A control method of an optical amplifier apparatus for compensating a gain characteristic of an optical amplifying medium. The control method includes providing an active gain characteristic actively which is a reverse of a characteristic in gain of the optical amplifying medium, and flattening the gain characteristics possessed by the optical amplifier apparatus at a predetermined value.

Abstract: An L-band optical amplifier has a rare earth doped gain medium including a filter distributed over a finite physical portion of the gain medium. The filter is distributed over between about 25% to substantially the entire length of the gain medium. The distributed filter substantially eliminates out-of-band light emission (C-band ASE, 1520 nm-1565 nm) and thus improves the performance of L-band amplification (1565 nm-1620 nm). Examples of distributed filters include discrete type filters such as long period gratings, or continuous type filters such as rare earth doped, twin core fibers, non-adiabatically tapered fibers and coaxial resonant ring fibers.

Abstract: Methods and systems for reducing a first tilt of a spectrum of light transmitted via an optical fiber are provided. To reduce the first tilt, an amplifier, such as an erbium doped fiber amplifier, is configured to yield a gain spectrum with an opposite tilt to that of the first tilt. When light traverses the fiber by passing the amplifier, the first tilt of the spectrum and the opposite tilt of the gain spectrum cancel partially or totally, thereby reducing the first tilt.

Abstract: The present invention relates to an arrangement and a method relating to optical channel equalizers. The channel equalizer includes at least one Q-port direction-dependent router (40), where Q≧3, one N-channel WDM (de)multiplexer (30), where N≧2, N-number of amplifying waveguides (31, 32, 33, 34, 35, 36, 37 and 38), at least N-number of fiber amplifiers (51, 52, 53, 54, 55, 56, 57 and 58), at least N-number of Bragg gratings (61, 62, 63, 64, 65, 66, 67 and 68), at least N-number of variable optical pump laser attenuators (71, 72, 73, 74, 75, 76, 77 and 78), at least one optical splitter (20 and 22) and at least one pump laser (10, 12, 14 and 16) per optical splitter (20 and 22). At least one of the ports (42, 44 and 46) on the direction-dependent router (40) is disposed on a first side of the WDM (de)multiplexer (30).

Abstract: The present invention relates to an optical filter and the like, applicable to a gain equalizer for equalizing the gain of an optical amplifier as well, comprising a structure enabling a repeater and the like to have a small-sized, inexpensive configuration This optical filter 22 has such a transmission spectrum that a ripple of 1 dB or more exists with respect to light in a communication wavelength band This transmission spectrum is designed so as to yield a transmissivity of −10 dB or less in both of a first blocking wavelength band having a bandwidth of 20 nm or more located on the shorter wavelength side than the communication wavelength band, and a second blocking wavelength band having a bandwidth of 20 nm or more located on the longer wavelength side than the communication wavelength band The optical filter having such a transmission spectrum can function as a filter for blocking noise light and as a gain equalizer

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: Methods and systems for reducing a first tilt of a spectrum of light transmitted via an optical fiber are provided. To reduce the first tilt, an amplifier, such as an erbium doped fiber amplifier, is configured to yield a gain spectrum with an opposite tilt to that of the first tilt. When light traverses the fiber by passing the amplifier, the first tilt of the spectrum and the opposite tilt of the gain spectrum cancel partially or totally, thereby reducing the first tilt.

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 dynamic gain equalizer using amplification instead of attenuation is disclosed. The device relies on integrated semiconductor optical amplifiers in line with a demultiplexer on a single integrated substrate for performing equalization of signals within each of a plurality of channels.

Abstract: An optical amplifier with a flattened wideband response is obtained by coupling counter-propagating pumping energy into an optical waveguide to cause Raman amplification in the optical waveguide, and by reflecting an amplified signal received from the optical waveguide into an output waveguide using a reflector having a spectral characteristic that is complementary to the spectral gain characteristic of the Raman amplification.

Abstract: A wavelength-selective filter, such as a narrow bandpass filter, is used to filter both the input and output of an optical amplifier. The selected channel is amplified and can be re-combined with the other original channels or provided to another output, depending on amplifier configuration. In a particular embodiment, a two-stage amplifier with center stage access uses a single gain-flattening filter to compensate for gain tilt of both amplifier stages.

Abstract: Disclosed is a fiber optic filter that includes a central core, a ring core concentric with the central core, an inner cladding region of refractive index ni between the central and ring cores, and a cladding layer of refractive index nc surrounding the ring core. The maximum refractive index n1 of the central core and the maximum refractive index n2 of the ring core are greater than nc and ni. The propagation constants of one core mode and one ring mode are different at wavelengths except for at least one wavelength &lgr;0 whereby power transfers between the two cores at &lgr;0. At least a portion of the fiber optic filter fiber is wound around a reel to subject it to a continuous curvature, the radius of which determines the amplitude of the attenuation. Such fibers are useful in fiber amplifiers in which the central core contains active dopant ions.

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: Optical amplifiers and methods for manufacturing optical amplifiers are provided that allow amplifiers to be fabricated to match design expectations. Optical amplifiers may be manufactured by assembling passive optical components in the amplifier before assembling active optical components such as doped fiber coils. Passive losses may then be characterized and used to calculate the lengths of the fibers that should be used in the amplifier gain stages. Following corrections to the nominal doped-fiber lengths based on the measured passive losses, the passive and active components of the amplifier may be assembled and characterized. Final corrections may be made to the amplifier assembly based on these characterizations. For example, the lengths of one or more of the doped fibers may be adjusted. If desired, such length adjustments may be made to fiber coils in the mid-stage portion of the amplifier, so that the impact on the operating characteristics of the amplifier are minimized.

Abstract: An optical amplifier arrangement having at least one optical amplifier stage (V1, V2) and a variably settable attenuator (VDL), whose attenuation spectrum (DV2, DV3, DV5, DV6) assumes an attenuation profile (DV2, DV3, DV5, DV6) that increases or decreases proportionally to wavelength. To reduce tilt of the channel level spectrum of an optical transmission signal, the profile of the attenuation spectrum (DV2, DV3, DV5, DV6) is variably settable. An advantageous structure of the variably settable attenuator according to the invention is furthermore specified.

Abstract: The optical amplifier includes 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 pump operates at a pump wavelength that has a lower inversion saturation than the highest wavelength of absorption of the first gain medium. 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.

Abstract: An optical amplifier device intended for WDM light signals comprises a preamplifier (3) and a power amplifier (11) of the optical fiber amplifier type, which are connected in series and have gain curves dependent on the wavelength. A controllable attenuator (5) is connected between the amplifiers (3 and 11) and is controlled by a control device (7). The signal input to the preamplifier (3) has a low power and is amplified to provide an output signal where the signals of the input channels have been amplified with different gains. The input signal of the power amplifier (11) then has a larger power resulting in a gain characteristic different from that of the preamplifier (3). By adapting the attenuation of the attenuator (5) for variations in the input signal the gain characteristic of the power amplifier (11) can be set so that the signal output from the amplifier device has a spectral dependence that is the same as the original spectral dependence obtained without variations.