Abstract: The invention provides an optical fiber amplifier which assures stable operation of a pump light source and efficiently makes use of residual pump power to achieve improvement in conversion efficiency. The optical fiber amplifier includes a rare earth doped fiber. Pump light from a pump light source is introduced into one end of the rare earth doped fiber by way of a first optical coupler, and residual pump light originating from the pump light and arriving at the other end of the rare earth doped fiber is applied to the other rare earth doped fiber amplifier or the loss compensation of a dispersion compensating fiber by Raman amplification.

Abstract: A device for generating amplified laser pulses includes at least one pulse laser controlled by at least a switch unit transmitting a master laser beam spatially multiplexed into elementary laser beams which are amplified in parallel by at least two optical amplifiers, wherein each of the amplified elementary laser beams is directed towards a single focussing volume. Each optical amplifier includes a fibre with photon layers, at least one optical pumping unit laser diode producing at least one pump wave for longitudinally pumping the fibre and one element for focussing in the focussing volume the amplified beam generated by the fibre, the silica or glass elongated fibre including a doped core, the pumping of each optical amplifier is continuous and the generation of the amplified optical pulses is obtained directly by the pulse laser.

Abstract: An optical fiber communication system is provided which uses remote pumping that is capable of improving pumping efficiency and reducing a noise figure. A coupler (20) of a linear repeater (18) couples signal light to pumping light outputted from a pumping light source (19). The outputted signal light and pumping light reach a linear repeater (25) through transmission fibers (22 to 24) and remote pumping modules (27F and 27R). A coupler (30) of the linear repeater (25) couples the signal light to the pumping light supplied from a pumping light source (29), to output the signal light and the pumping light to the transmission fiber (24). The remote pumping module (27F) divides the pumping light propagated in the transmission fiber (22), from the signal light. The remote pumping module 27F branches the divided pumping light in two directions with a predetermined ratio. After branching, each of the branched pumping light is coupled to the signal light to be supplied to both ends of an erbium-doped fiber.

Abstract: An optical amplifier assembly for submarine applications. The optical amplifier assembly comprises: a first and a second double stage fiber amplifier with respective first and second fiber amplifiers for amplifying optical signals (OS, OS?) each propagated on a respective optical fibre, said optical fibres being operated in opposite operating directions (W-E, E-W), and a common pump source comprising a plurality of pump light sources, the common pump source being coupled via a coupler as a co-propagating pump to the first and second fiber amplifiers of the first and second double stage fiber amplifiers. The proposed optical amplifier assembly further comprises a gain flattening filter between the two fiber amplifiers of the first and second double stage fiber amplifiers. Thus the proposed optical amplifier assembly presents an increased efficiency with respect to an output power at a constant pump power and allows to adjust the pump power for maintaining a given output power without excessive NF degradation.

Abstract: A wavelength division multiplexed optical amplifier, enabling elimination of the problems of oscillation and fluctuation in output due to ASE at the time of a rapid change in the number of input wavelengths, provided with a first-stage optical amplifying unit, second-stage optical amplifying unit, a common AGC circuit for common AGC of the first and second optical amplifying units, and a pumping light distribution means for applying pumping light to the first and second-stage optical amplifying units with a predetermined distribution ratio.

Abstract: An optical component for gain-flattening multiplexed passband signals amplified with optical pump power, comprises a launch port optical waveguide operative to communicate multiplexed passband signals in a passband wavelength range and optical pump power in a different wavelength range; a thin film demux filter oriented to receive combined multiplexed passband signals and optical pump power from the launch port optical waveguide, and operative to pass the multiplexed passband signals and to reflect the optical pump power; a bypass port optical waveguide operative and oriented to receive and carry optical pump power reflected by the demux filter; a gain-flattening filter positioned to receive from the thin film demux filter and operative to pass the multiplexed passband signals with a desired attenuation profile for gain-flattening; and an output port optical waveguide oriented to receive and operative to carry at least multiplexed passband signals passed by the gain-flattening filter.

Abstract: Apparatus for optically pumping a clad amplifier fiber includes one or more transmission fibers arranged and configured to insert pump-light from a pump light source such as a diode-laser into the cladding of the amplifier fiber. The pump light propagates through the cladding and a portion of the pump light is absorbed in the doped core of the amplifier fiber. At least one of the transmission fibers is arranged to receive an unabsorbed portion of the propagated pump light from the amplifier cladding and re-insert the unabsorbed portion of the pump-light into the cladding for re-propagation through the cladding. This provides that pump light that would otherwise be wasted is circulated through the amplifier fiber for further absorption by the amplifier core.

Abstract: A pulsed fiber laser and associated electronics contained in a miniature package is disclosed. The Pulsed Fiber Laser Source (PFLS) can be a single-stage high gain master oscillator power amplifier (MOPA) type fiber laser source. The PFLS can include a distributed feedback (DFB) laser, a narrowband optical filter, a broad area high-power pump diode, and Erbium/Ytterbium (Er/Yb) double cladding doped fiber. Input electrical pulses drive the DFB laser diode to emit optical pulses that are then amplified by the optical amplifier. Active and passive cooling elements may be incorporated for continuous operation without rest time. Passive cooling for intermittent pulsed applications allows the laser source to be miniaturized by eliminating active cooling elements and associated power supplies and controllers. Low duty cycle relaxes drive requirements and further reduces the size.

Abstract: Disclosed is a gain-providing optical power equalizer which can equalize optical channel output or gain while amplifying signal output. In prior art technologies, optical power equalization has been achieved by attenuating signal output differently depending upon optical channels. However, the optical power equalizer of the present invention is characterized in that it achieves equalization of optical power by giving optical gain differently depending upon optical channels. According to the present invention, the output of optical channels can be adjusted to be flat or as desired without deteriorating signal to noise ratio.

Abstract: An optical amplifier and a laser generator based on the fiber side-polished technology having a high pumping efficiency, a low noise figure and a small footprint are provided in this application. The optical amplifier and the laser, which have a very long effective interaction length in conjunction with highly doped Erbium glass attached to its surface and an addition of a slanted fiber grating inscribed in the guiding core at the polished region can spatially separate the signal and pump power to simultaneously improve the pumping efficiency and optimize the penetrated depth of the signal evanescent-field. The spontaneous emission is kept from being amplified and therefore a high quality amplified signal is produced.

Abstract: A Raman amplifier for use in an optical fiber communication system with dispersion compensation has a first order Raman pump source and a second order Raman pump source both coupled to the input ports of a four-port optical coupler having two input ports and two output ports. One output port is connected to an optical fiber length to inject a pump light signal into the fiber length for second-order Raman amplification and the other output port is connected to a dispersion compensating fiber.

Abstract: A wideband erbium-doped optical fiber amplifier is disposed among an optical fiber through which a first and second band-band optical signals (for example, the C-band and L-band) are transmitted and forms a first optical path and a second optical path parallel to each other. The wideband erbium-doped optical fiber amplifier comprising a first amplifying section disposed on the first optical path, including a first erbium-doped optical fiber to amplify the first-band optical signals, a filter to gain-flatten the amplified first-band optical signals, wherein a reflected portion of the first band optical signal by the filter is directed to the second optical path; and a second amplifying section disposed on the second optical path, having a second erbium-doped optical fiber to amplify received second-band optical signals, wherein the reflected first-band optical signal is used to pump the second erbium-doped optical fiber.

Abstract: A long-wavelength band (L-band) optical amplifier capable of maintaining a gain constant, thereby providing a stable optical output even when an optical power or a wavelength of a signal input thereto changes. The optical amplifier includes an amplifier which amplifies an input signal, and an amplified spontaneous emission (ASE) reflector which reflects backward ASE generated by the amplifier so that the backward ASE is fed back to the amplifier.

Abstract: A multiple stage Raman amplifier includes an interstage wavelength-selective pump combiner. Wavelength-selection characteristics are such that the pump combiner substantially blocks the passage of the pump signal of the first stage to the second stage and/or vice versa while allowing the passage of the transmission signal from the first stage to the second stage. The pump combiner substantially blocks different portions of the wavelength spectrum of the pump radiation which is fed into the pump combiner from different ports. The pump combiner preferably includes thin-film filters. The pump combiner has the multiple function of coupling the pump signal of the first (or second) pump source and of isolating from one another the pump signals of the two amplification stages. This allows the reduction of the number of passive components present in a multistage optical amplifier, which in turn leads to a decrease of the overall insertion loss in the amplifier and to shorter assembly processing.

Abstract: An optical amplifier comprises a device substrate, a first waveguide embedded in the device substrate, and a plurality of lasers. The lasers are positioned to provide a first plurality of light beams substantially transverse to the first waveguide.

Abstract: Disclosed are optical signal transmission apparatus including a reflective gain-clamped semiconductor optical amplifier and optical communication system using the optical signal transmission apparatus, which can improve modulation speed and optical power by effectively suppressing intensity noise of an incoherent light source.

Abstract: Optical pumping unit comprising a first pump source adapted to emit a first pump radiation at wavelength ?p1; a second pump source adapted to emit a second pump radiation at wavelength ?p2, with wavelength ?p2 different from wavelength ?p1; and a common coupling section comprising a first and a second port connected to the first and second pump source for respectively receiving the first and the second pump radiation; a third port for a signal radiation at wavelength ?s; a fourth port, wherein the coupling section is adapted to combine, in the fourth port, the signal radiation and the first and second pump radiation through a reversal of the direction of propagation of the first pump radiation from the first port to the fourth port.

Abstract: Optical systems of the present invention includes power sources that provide dedicated and shared power to a plurality of optical amplification sections. In various embodiments, multiple optical pump sources are provided the include a plurality of optical sources, which supply dedicated optical pump power and shared optical pump power to two or more optical amplification sections. In other embodiments, remote dispersion compensation is performed and Raman amplification is provided to overcome at least a portion of the loss.

Abstract: Disclosed is a wide-band fiber amplifier for amplifying C-band and L-band optical signals, including a first amplifying unit including a first amplifying fiber adapted to be (1) pumped in at least one direction (2) amplify both the C-band and L-band optical signals and (3) output Amplified Spontaneous Emission (ASE), a second amplifying unit including a second amplifying fiber adapted to be pumped by amplified ASE and secondarily amplify the amplified L-band optical signal, and an L-band pumping light source including a third amplifying fiber adapted to be pumped in at least one direction while being pumped by the ASE, and output amplified ASE used to pump the second amplifying fiber.

Abstract: An optical amplifying apparatus has a plurality of pumping sources generating pumping light beams at different wavelengths, a Raman amplification medium receiving the pumping light beams from the pumping sources to amplify a main signal light beam by using stimulated Raman scattering phenomenon due to the pumping light beams, a rare-earth-doped optical amplification medium receiving the main signal light beam amplified by the Raman amplification medium to further amplify it, and a pumping light introducing means introducing a part or all of a pumping light beam at a specific wavelength of the pumping light beams as a pumping light beam for the rare-earth-doped optical amplification medium to the rare-earth-doped optical amplification medium. The optical amplifying apparatus in a smaller size and with less fluctuation in the optical output power can readily send monitoring control information irrespective of presence of the optical input power.

Abstract: Disclosed wideband optical fiber amplifier amplifies and outputs wideband optical signal containing C-band and L-band optical signals. The amplifier includes: a first amplification section amplifying the wideband optical signals; a second amplification section amplifying the separated L-band optical signals amplified by the first amplification section; an optical signal coupler combining and outputting the optical signals amplified by the first and second amplification sections; and an optical circulator.

Abstract: Apparatus for optically pumping a clad amplifier fiber includes one or more transmission fibers arranged and configured to insert pump-light from a pump light source such as a diode-laser into the cladding of the amplifier fiber. The pump light propagates through the cladding and a portion of the pump light is absorbed in the doped core of the amplifier fiber. At least one of the transmission fibers is arranged to receive an unabsorbed portion of the propagated pump light from the amplifier cladding and re-insert the unabsorbed portion of the pump-light into the cladding for re-propagation through the cladding. This provides that pump light that would otherwise be wasted is circulated through the amplifier fiber for further absorption by the amplifier core.

Abstract: A dual fiber optic amplifier uses a single pump source for two or more optical power amplifiers. The dual fiber optic amplifier includes a pump source that emits light, a pump splitter, a first optical power amplifier and a second optical power amplifier. The pump splitter splits the light emitted by the pump source into two or more portions. The first optical power amplifier includes an optical fiber input, an optical fiber output, and a doped fiber portion, wherein the first portion of light from the splitter is coupled into the optical fiber input of the first optical power amplifier. The second optical power amplifier includes an optical fiber input, an optical fiber output, and a doped fiber portion, wherein the second portion of light emitted from the splitter is coupled into the optical fiber input of the second optical power amplifier.

Abstract: An optical fiber amplifier whose characteristics are stable is provided. The optical fiber amplifier provides a short wavelength transmitting coupler that multiplexes pumping light inputted from its forward side and inputted signal light, an EDF that amplifies the signal light inputted from the short wavelength transmitting coupler, a narrow-band coupler that multiplexes the signal light and the pumping light in the transmission band of the narrow-band coupler, a splitting coupler that splits the inputted pumping light at a designated ratio, and a pumping light LD that outputs the pumping light for amplifying the signal light. With this structure, at the optical fiber amplifier that amplifies many wavelengths together being adopted at the WDM transmission, even when the number of input signals is changed, the deterioration of noise figure is avoided.

Abstract: A thulium-doped fiber amplifier is disclosed and includes a thulium-doped fiber to amplify optical signals belonging to S-band, a first pumping unit to output amplified spontaneous emission that represents a peak value in a predetermined wavelength range belonging to C-band, to pump the thulium-doped fiber, and a second pumping unit to output pumping light belonging to the wavelength band different from the C-band to pump the thulium-doped fiber.

Abstract: An integrated optical device is provided for distributing optical pump energy. The device includes at least one input port for receiving optical energy, a plurality of output ports, and a user configurable optical network coupled to the input port for distributing the optical energy among the output ports in a prescribed manner in conformance with a user-selected configuration.

Abstract: Optical systems of the present invention generally include at least one optical amplifier having a first pump source configured to supply power to said amplifier via a first pumping paths. A second pumping path is provided to supply power to the amplifier from a second pump source configured to replace power from the first pump source. The amplifier allows the replacement and repair of a pump source during operation by providing in-service hot swap capability, which increases the overall availability of the amplifier. The pump source can also be changed during operation to allow reconfiguration of the optical system.

Abstract: An amplifying optical element for use within an optical fiber communication system is disclosed which includes a doped optical fiber, an optical excitation source which is physically integrated with and immediately adjacent to and surrounding doped optical fiber, the excitation source being capable of emitting sufficient light to enable power gain of the signal being transmitted, and an external power source electrically connected to the optical excitation source for initiating and maintaining the light emission. Preferably, the excitation source is a multilayer electrically conductive structure which includes a first layer immediately adjacent to the doped optical fiber, wherein the first layer is a transparent, electrically conductive material, a second layer adjacent to the first layer, wherein the second layer is an electroluminescing material, and a third layer adjacent to the second layer, wherein the third layer is an electrically conductive material.

Abstract: This invention relates to an optical fiber for amplification suitable for amplifying signals in the L-band, an optical fiber amplifier including the optical fiber, and an optical transmission system. The optical fiber amplifier according to the invention includes a silica-based optical fiber as an optical fiber for amplification, which has a core region doped with Er and Al. The optical fiber for amplification has an Er concentration of 1,500 wt.ppm or less, and has the characteristics at a wavelength of 1.53 ?m of: an absorption loss of 10 dB/m or more but 25 dB/m or less; and an unsaturated absorption of 900 dB or less.

Abstract: Disclosed is dispersion-compensated erbium-doped fiber amplifier.

Abstract: An optical repeater is provided that includes at least four optical amplifiers each supplying optical amplification to an optical signal traveling in a different unidirectional optical fiber that collectively form at least two bi-directional pairs of optical fibers. The repeater also includes a first plurality of pump sources for providing pump energy to a first optical fiber located in a first of the optical fiber pairs and a second optical fiber located in a second of the optical fiber pairs. The first optical fiber and the second optical fiber support optical signals traveling in a common direction. A first combiner arrangement combines the pump energy from the first plurality of pump sources and distributes it to the optical amplifiers supplying amplification to optical signals traveling in the first and the second optical fibers.

Abstract: The invention provides an optical wavelength multiplex transmission method wherein a band in the proximity of a zero dispersion wavelength of an optical fiber is used and optical signals are disposed at efficient channel spacings taking an influence of the band, the wavelength dispersion and the four wave mixing into consideration to realize an optical communication system of an increased capacity which is not influenced by crosstalk by FWM. When optical signals of a plurality of channels having different wavelengths are to be multiplexed and transmitted using an optical fiber, a four wave mixing suppressing guard band of a predetermined bandwidth including the zero-dispersion wavelength ?0 of the optical fiber is set, and signal light waves of the plurality of channels to be multiplexed are arranged on one of the shorter wavelength side and the longer wavelength side outside the guard band.

Abstract: A method of amplifying a signal light includes initially multiplexing a signal light and a pumping light, initially amplifying the signal light initially demultiplexing so as to separately output the amplified signal light and the pumping light, and modifying a waveform of the amplified signal light so as to compensate for waveform distortion of the signal light along a transmission path of the signal light and providing an output of a waveform modified signal light. Thereafter, the waveform modified signal lights is secondarily multiplexed, secondarily amplified, and secondarily demultiplexed with a waveform of amplified signal light being compensated for waveform distortion of the signal light along a transmission path of the signal light and providing an output of a waveform modified signal light.

Abstract: An optical amplifier for amplifying WDM light which includes an optical fiber used as an optical amplification medium for amplifying WDM light. A pump light source is provided to generate pump light and an optical splitter is provided to generate first branch pump light and second branch pump light from the pump light. The optical amplifier further includes an optical device guiding the first branch pump light to the optical fiber and guiding the second branch pump light to a transmission line connected to an input side of the optical amplifier.

Abstract: In this invention we present a method and apparatus of simultaneously compensating a divider power-loss and managing the pump's power budget in upgradeable and scalable passive optical network architecture. The apparatus namely called lossless splitter, is passive, bi-directional and allows modular and scalable PON architecture. According to the preferred embodiment of the present invention a mean of dividing (combining) optical signals to (from) a plurality of paths in a lossless fashion is proposed. This divider (combiner) also as the property of distributing the residual optical pump power, needed for amplifier stage activation, to other dividers (combiners) in a chain. The incoming pump power may be provided by the signal transmission fiber or by a pump power transmission fiber. Applications of this lossless divider (combiner) are reviewed, alternative embodiments are proposed and system deployment/upgrade strategies are described.

Abstract: An integrated optical fiber amplifier system includes a non-reciprocal combination-device and an optical fiber amplifier. The non-reciprocal combination-device includes a first birefringent wedge, a second birefringent wedge, and a non-reciprocal rotating element. The optical fiber amplifier is optically coupled to the first birefringent wedge for receiving a combined pump light from the non-reciprocal combination-device.

Abstract: A method and apparatus for amplifying optical transmission signals is described. A bi-directional amplifier utilizes a pump feed-through signal from one of the optical pumps used to pump a first amplifying fiber to provide pump power to a second amplifying fiber. If an optical pump within the amplifier fails, this feed-through signal is used to pump the amplifying fiber directly pumped by the failed pump source.

Abstract: A method of amplifying optical signals comprising providing a plurality of input radiation signals into the inputs of a P×V coupler, each of the input radiation signals having a respective input radiation profile having a set of pump wavelengths and pump powers corresponding to the respective wavelengths, wherein at least one set is different from at least one other set; providing V output pump radiation profiles from the outputs of the P×V coupler; and amplifying an optical data signal by coupling at least one of the V output pump radiation profiles with the optical data signal, wherein at least one of the V output pump radiation profiles has a different power than at least one other of the V output pump radiation profiles.

Abstract: A method and system for providing a highly integrated hybrid component is disclosed. The method and system include providing a triple fiber collimator, a dual isolator/polarization beam deflector and a dual fiber collimator. The triple fiber collimator receives a plurality of pump signals in a first direction and outputs an optical signal in a second direction. The dual isolator/polarization beam deflector is optically coupled to the triple fiber collimator. The dual isolator/polarization beam deflector transmits the pump signals in the first direction, prevents a portion of the pump signals from traveling out of the triple-fiber collimator in the second direction, provides the optical signal in the second direction and prevents a portion of the optical signal from traveling out of the dual fiber collimator in the first direction. The dual fiber collimator receives the optical signal traveling in the second direction and outputs the pump signals traveling in the first direction.

Abstract: Systems and methods for ameliorating double Rayleigh backscattering induced impairments are provided. Raman amplification is divided among two or more stages. Optical energy from a single counter-propagating pump may traverse multiple stages while optical energy at the frequency of the signal to be amplified is permitted to propagate in the forward direction only. In this way the pump power can be effectively distributed over the entire amplifier length. The scheme may be implemented in a simple configuration employing a closed circulator and a fiber Bragg grating. Multiple wavelength pump operation may be accommodated as well as either discrete or distributed Raman amplification.

Abstract: An apparatus has first and second light sources, a plurality of filters, and an optical switch. The light sources output a light beam having a spectrum determined by a gain band thereof. The plurality of filters each have a reflection band included in the gain band. The optical switch selectively couples the filters to the light source. The first and second light sources provide pumping light to a single transmission line. The first and second filters are configured so as to not reflect signal light to be amplified.

Abstract: This invention describes new developments in Sagnac Raman amplifiers and cascade lasers to improve their performance. The Raman amplifier bandwidth is broadened by using a broadband pump or by combining a cladding-pumped fiber laser with the Sagnac Raman cavity. The broader bandwidth is also obtained by eliminating the need for polarization controllers in the Sagnac cavity by using an all polarization maintaining configuration, or at least using loop mirrors that maintain polarization. The polarization maintaining cavities have the added benefit of being environmentally stable and appropriate for turn-key operation. The noise arising from sources such as double Rayleigh scattering is reduced by using the Sagnac cavity in combination with a polarization diversity pumping scheme, where the pump is split along two axes of the fiber. This also leads to gain for the signal that is independent of the signal polarization.

Abstract: Optical systems of the present invention generally include at least one optical amplifier having a first pump source configured to supply power to said amplifier via a first pumping paths. A second pumping path is provided to supply power to the amplifier from a second pump source configured to replace power from the first pump source. The amplifier allows the replacement and repair of a pump source during operation by providing in-service hot swap capability, which increases the overall availability of the amplifier. The pump source can also be changed during operation to allow reconfiguration of the optical system.

Abstract: A multi-port optical amplifier chip has an inner cladding layer sandwiched between a pair of outer cladding layers, a plurality of active core elements disposed substantially within the inner cladding layer to receive optical signals at respective input ports and transmit amplified optical signals at respective output ports, a pair of reflecting surfaces on opposing sides of the inner cladding and at least one pump source. The pump source directs pump light into the inner cladding layer where it is confined to bounce back-and-forth across the active core elements thereby enhancing the absorption of pump light into the core elements, hence increasing gain. Greater than 5 dB over the C-band (1930 nm-1965 nm) in less than 10 cm is expected with a phosphate glass material co-doped with greater than 2 weight percent Erbium and 10 weight percent Ytterbium. A number of fiber drawing based approaches are contemplated for manufacturing the amplifiers to achieve this performance and reduce cost.

Abstract: Optical systems of the present invention include a plurality of optical processing nodes in optical communication via a plurality of signal varying devices. A first signal varying device includes an optical fiber configured to produce Raman scattering/gain in a signal wavelength range and a first signal variation profile. A first pump source is configured provides sufficient pump power in a plurality of first pump wavelengths to stimulate Raman scattering/gain in the optical fiber within the signal wavelength range. A second signal varying device is provided having a second signal variation profile to produce a cumulative signal variation profile that differs from the first and second signal variation profiles.

Abstract: An optical amplifier array is integrated with a switching matrix with a tunable filter. As a result, switching and amplification can be performed in a common hermetic package, for example, thus offering advantages associated with small footprint and low cost. The optional integration of the tunable filter, with or without the switching matrix, further allows for the monitoring of the separate optical links to ensure the proper routing of signals and/or proper spectral slotting of the various channels in each of the WDM optical signals.

Abstract: A method of amplifying a signal light includes initially multiplexing a signal light and a pumping light, initially amplifying the signal light initially demultiplexing so as to separately output the amplified signal light and the pumping light, and modifying a waveform of the amplified signal light so as to compensate for waveform distortion of the signal light along a transmission path of the signal light and providing an output of a waveform modified signal light. Thereafter, the waveform modified signal lights is secondarily multiplexed, secondarily amplified, and secondarily demultiplexed with a waveform of amplified signal light being compensated for waveform distortion of the signal light along a transmission path of the signal light an output of a waveform modified signal light. The waveform modified signal light is thirdly multiplexed and thirdly amplified so as to provide an output of amplified waveform modified signal light.

Abstract: In a distributed Raman amplification system, the pump laser and the fiber are chosen so as to have characteristics which result in broadening of the DRBS. For example, with a transmission fiber through which signal light of a wavelength &lgr;s propagates, and having zero dispersion at a wavelength &lgr;o; a pump laser producing counterpropagating pump light at a wavelength &lgr;p; where &lgr;p and &lgr;s are on opposite sides of the zero dispersion wavelength is used. The transmission fiber may be large effective area fiber. In a Raman amplification system suitable for use in a WDM optical fiber communication system, pump lasers having mode spacing which is less than the optical bandwidth of the signal channel have been found to be advantageous.

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: An L band optical amplifier in disclosed. The optical amplifier includes a signal line which has an input, an output disposed optically downstream of the input, and an amplifying gain medium optically disposed between the input and the output. The optical amplifier further includes a laser optically connected to the first amplifying gain medium and an apparatus for directing C band light into the amplifying gain medium.