Abstract: A broadband semiconductor optical amplifier (SOA) device includes at least two gain-clamped SOAs having different spectral responses. The gain-clamped SOAs are coupled so that the broadband SOA device has a spectral response which is not attainable by any one of the gain-clamped SOAs. The gain-clamped SOAs may be coupled in different ways. For example, they may be coupled in parallel, in series, or in another different and/or more complex ways. In one implementation, the gain-clamped SOAs are vertically lasing semiconductor optical amplifiers.

Abstract: Power transient control in an optical network by power measurement and prediction with a simple-to-compute model to drive an optical filter control.

Abstract: An optical amplifier module that is insensitive to polarization comprises a first fiber, a second fiber, a semiconductor optical amplifier (SOA), and a polarization dependent loss (PDL) unit. The first fiber provides for optical input to the SOA. The SOA amplifies the optical signal received and outputs the amplified signal. The output of the SOA is optically coupled to the PDL unit. The PDL unit provides polarization dependent loss and the loss is preferably selected to match the polarization dependent gain of the SOA such that when two are coupled there is no overall polarization dependence. The output of the PDL is optically coupled to the fiber for transmission output.

Abstract: A method for dynamically compensating for signal loss and dispersion in an optical signal traversing though an optical network. The method includes providing a dynamic gain equalization filter (DGEQ) having a dynamically adjustable transfer function, and providing a first optical amplifier and a second optical amplifier interconnected by the DGEQ to form a dynamic amplifier site in the optical network. The method further includes controlling spectral power profile of the optical signal at an output of the dynamic amplifier site by dynamically adjusting a transfer function associated with the DGEQ.

Abstract: In one aspect of the invention, a method of amplifying optical signals includes identifying one of a plurality of pump signals driving an amplification system as a failing pump signal comprising a reduced power compared to a normal power of the failing pump signal. The method further includes adjusting the power of at least one other of the plurality of pump signals based at least in part on the failing pump signal to at least partially compensate for a degradation of performance of the amplification system that would otherwise be caused by the reduction in power of the failing pump signal.

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: Optical channel monitor depolarizers are provided. The depolarizers may be used to reduce the effects of polarization-dependent loss on optical channel power measurements made in optical amplifiers or other optical network equipment. The channel power measurements may be used in controlling optical amplifiers and other equipment in wavelength-division-multiplexing communications links.

Abstract: In an optical amplifier using a rare earth element-doped optical fiber such as an erbium-doped optical fiber, a variation of amplification gain resulting from temperature change is suppressed and the gain-temperature characteristic is enhanced. Moreover, the quantity of temperature compensation in the gain is easily adjustable. Light from an excitation light source is input to an optical fiber for optical amplification comprising a rare earth element-doped optical fiber, via a temperature compensation optical fiber comprising a rare earth element-doped optical fiber such as an erbium-doped optical fiber. By changing the length of this temperature compensation optical fiber, the quantity of temperature compensation is finely adjusted.

Abstract: An inexpensive broadband source such as an ASE source, used for erbium amplifier measurements, compares well with the use of a prior art ITU grid. Deltas are less than 0.4 and 0.3 dB for gain and noise figure respectively. The spectral loading used to test erbium amplifiers needs to closely resemble conditions seen in the field. Use of an ITU grid is a good way of achieving this, however it is a costly solution and may restrict the spectral resolution. Use of a high power amplified spontaneous emission source gives a cost-effective alternative, which compares well with ITU grid measurements. In addition the spectral resolution of the measurement is then only limited by the spectral resolution of the optical spectrum analyzer.

Abstract: Semiconductor optical amplifiers (SOAs) are cheaper to manufacture, control and test than other types of optical amplifier such as erbium doped fiber amplifiers (EDFAs). However, SOAs are non-linear in the respect that the gain of an SOA is not constant for different input or output signal powers. This is a significant problem because cross-talk between channels occurs as a result. It is known that the gain of SOAs can be clamped by integrating a vertical cavity surface emitting laser (VCSEL) with the SOA such that their active regions are shared. The present invention enables the physical length of such devices to be increased in such a manner that the saturation output power is increased whist retaining the gain clamping effect. This is achieved by using two or more contact points on the device at which different drive currents are applied.

Abstract: A method and system is disclosed of characterizing an optical amplifier for operation with a required tilt or curvature within predetermined limits. As the temperature of the erbium-doped optical amplifier is varied while a test signal is launched into the amplifier accompanied by a pump signal the output spectrum is compared with a desired spectrum. At different temperatures different measures of tilt or curvature are present at the output port of the amplifier in the presence of an input signal at the input port. Feedback related to the measure of tilt or curvature of at least one of the plurality of different temperatures is provided in the form of a feedback signal or an information signal.

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: An optical fiber amplifier includes an optical system and an electronic controller. The optical system includes: an optical gain medium; at least one pump source coupled to the optical gain medium; an input port for in-coming signal; and an output port for an out-going signal. It also includes an input optical signal tap coupled to a first optical detector; and an output optical signal tap coupled to a second optical detector. The electronic controller is adapted to utilize inputs received from the tabs to control optical power provided by the pump source. The controller includes a user interface that allows a user to control at least one of the following available functions: desired amplifier gain value; amplifier output power value; ASE noise compensation.

Abstract: Optical detector components in a fiber-optic communication system are temperature stabilized. The optical detector components may be part of an optical amplifier, a receiver, or other optical device. A temperature-controlled housing may be used to stabilize the temperature of a photodiode and/or a transimpedance amplifier of the optical detector. The housing may additionally be used to stabilize the temperature of the coils of a fiber optic amplifier and possibly other components.

Abstract: The object of this invention is to improve SNR in the Raman amplification. An optical fiber (10) consists of a dispersion shift fiber in which a zero dispersion wavelength is shifted to the 1.55 &mgr;m band, and an optical fiber (12) consists of a single mode optical fiber having the effective core area of 100 &mgr;m2 which is larger than that of the optical fiber (10). An optical coupler 14 is disposed at the optical signal emission end of the optical fiber (12). A laser diode (16) outputs the laser light of 1455 nm as a Raman pumping light source. The output light from the laser diode (16) is introduced into the optical fiber (12) from the back, namely in the opposite direction to that of the optical signal propagation. The ratio of the Raman gain coefficient of the optical fiber (12) to that of the optical fiber (11) should be 1/1.08 or less, preferably 1/1.1 or less.

Abstract: A method for amplifying optical signals and an optical fiber amplifier for accomplishing the same. An optical fiber is coupled to a source of pump light and a signal gain level is correlated to a dispersion value of the optical fiber that corresponds to a local minimum power level of a cross-talk signal generated by four wave mixing. Optical signals are transmitted through the optical fiber while admitting sufficient pump light into the fiber from the source to attain the selected Raman gain level.

Abstract: A signal transmission system has a number of wave division multiplex optical carriers linking a number of switching units arranged in a closed ring network. The carriers are amplified to compensate for loss and attenuation, but the ring gain of each carrier must be less than unity to prevent unwanted signal oscillation. An automatic gain control arrangement is operative for each optical carrier which is detected as being present at a switching unit, and the gain control is disabled for each carrier which is detected as being absent.

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: An erbium doped fiber amplifier that includes two separate variable optical attenuators that provide signal attenuation to eliminate spectrum tilt of the amplified optical signal. The erbium doped fiber amplifier includes a first pre-amplifier stage, a second pre-amplifier stage and a power amplifier stage. A primary variable optical attenuator is positioned between the first pre-amplifier stage and the second pre-amplifier stage, and a secondary variable optical attenuator is positioned between the second pre-amplifier stage and the power amplifier stage. By providing two separate variable optical attenuators at two different locations, the internal loss variation in the erbium doped fiber amplifier is averaged to provide an improved amplifier design and noise figure performance.

Abstract: Light signals of first to n-th bands amplified en bloc undergo proper attenuation through an adjustable optical attenuator in conformance with attenuation in an optical fiber connected to input of an optical amplifying repeater apparatus, whereon the light signals are demultiplexed or separated into individual bands and amplified by first to n-th fixed-gain optical amplifiers (#1, . . . , #n) each having a high fixed gain in the respective bands to be subsequently multiplexed by an optical multiplexer and then sent out onto a transmission line. A monitoring light branching device extracts a part of light power of a specific monitoring wavelength, which is then fed to an adjustable attenuator control circuit which controls the attenuation factor of the adjustable optical attenuator so that the light power of the specific wavelength remains constant. The gain of the optical amplifying repeater apparatus at the specific wavelength can thus be determined.

Abstract: A WDM ring transmission system is provided whereby each optical signal is first dropped from the ring, supplied to an amplifier, and then input to an optical receiver. Typically, a filtering element is also provided either prior to or after the amplifier. The amplifier increases the power of the transmitted optical signal so that the optical signals can be transmitted over greater distances, and the filtering element minimizes any adjacent channel cross-talk light fed to the receiver. Moreover, since the amplifier only amplifies the dropped channel, excessive noise accumulation due to non-uniform spectral gain can be avoided. In addition, channels can be arbitrarily assigned to add/drop elements along the ring.

Abstract: In an optical amplifier for use in, for example, a wavelength multiplexing optical communication system, in order to allow an excitation light source to be enlargeable or removable in accordance with an increase/decrease in the number of channels in signal light even if the optical communication system is in operation, there are included an optical amplifying section (2) for amplifying and outputting inputted signal light, a plurality of excitation light sources (3, 4) and an excitation light source control section (5) for controlling operations of the excitation light sources (3, 4), wherein the excitation light sources are composed of a main excitation light source (3) and an auxiliary excitation light source (4), and the excitation light source control section (5) is equipped with a control section (7) which, when the number of channels in the inputted signal light is equal to or less than a predetermined number of channels, executes control whereby the main excitation light source (3) supplies excitation

Abstract: The effects of optical impairments on optical signal transmission are substantially reduced in a lightwave transmission system by positioning optical amplifiers and network elements in respective upstream-downstream combinations. By placing an optical amplifier at a position upstream from its corresponding network element, sufficient amplification can be provided by the optical amplifier to compensate for losses introduced by its corresponding network element. Advantageously, the corresponding downstream network element provides sufficient attenuation of the forward travelling lightwave signals so that power-dependent nonlinear effects in the optical fiber do not significantly distort the lightwave signals.

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: A method of increasing usable bandwidth on a long-haul cable system having at least one optical fiber, the method comprising the steps of: (a) effecting counter-propagating first and second signals of different bands on a common long-haul optical fiber having cascaded optical amplifiers; and (b) band amplifying the first and second signals while reducing BRS in the bands.

Abstract: A method and apparatus for optical amplification with a large dynamic gain range in both the non-linear (1530-1540 nm) and linear (1540-1565 nm) regimes of the C-Band. The large dynamic gain range is achieved by the synergistic operation of a dual-stage Erbium-doped Fiber Amplifier (EDFA) having a self-saturating Thulium-doped fiber inserted between the two stages. The Thulium-doped fiber saturation is determined by the output power of the first EDFA stage, and the synergistic, combined operation of both EDFA stages and the self-saturating absorber is controlled by appropriate algorithms and software.

Abstract: A system for reducing reflection of an optical system can reduce or eliminate reflection at facets of a semiconductor gain medium and can suppress natural longitudinal modes produced within the semiconductor gain medium. In combination with external feedback, the system can allow more precise wavelength control of the light output of a laser, thereby allowing the laser to be used in a dense wavelength division multiplexing system. The system employs a patterned relief surface disposed on a facet of a gain medium. The patterned relief surface may be a “motheye” pattern having a plurality of conical posts disposed on the surface of the facet. The system may be combined with conventional devices, such as a Bragg reflector or a microelectromechanical component, to further improve wavelength control of a resonant optical cavity, thereby improving the operation of optical communications systems.

Abstract: A method of assembling an optical system includes the steps of: (i) selecting, from a plurality of optical fibers characterized by a common nominal cut-off wavelength &lgr;cn and an actual cut-off wavelength &lgr;c such that the cut-off wavelength &lgr;c of each one of this plurality of fibers is the same as the nominal cut-off wavelength &lgr;cn or differs slightly from the nominal cut-off wavelength due to manufacturing tolerances, only fibers with &lgr;c>&lgr;min, where &lgr;min is a predetermined minimum acceptable cut-off wavelength of the selected fibers; and (ii) bending at least one section of at least one of these selected fibers such that this bent section has a bend radius R, where 12 mm<R<18 mm.

Abstract: Optical amplifier equipment for operation in fiber-optic communications networks is provided. The optical amplifier equipment may include one or more gain, stages based on rare-earth-doped fiber or Raman-pumped fiber. The gain stages may be optically pumped using diode lasers. Optical monitors may be used to measure optical signals in the optical amplifier equipment. Input signals and output signals may be measured. A control unit may adjust the pump powers in the gain stages based on the measured optical signals to suppress gain transients. An optical delay line may be used to provide additional time for the control unit to process the optical signals before adjusting the pump powers. A midstage module including dispersion-compensating fiber may be installed in the optical amplifier equipment. The control unit may automatically detect the amount of optical delay associated with the installed module and may control the pump powers accordingly during transient control operations.

Abstract: In order to be able to use a semiconductor light amplifier of conventional type and operating under gain saturation conditions while nevertheless providing constant gain for an optical signal to be amplified, the device comprises means for producing a compensation light wave and coupling means for injecting the optical signal to be amplified and the compensation light wave into the amplifier. The compensation light wave presents amplitude modulation such that when combined with the optical signal to be amplified the overall amplitude modulation is eliminated or at least attenuated. The device is applicable to optical transmission systems operating at a single wavelength or with wavelength division multiplexing.

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

Abstract: A hybrid amplifier reduces the noise generated by the hybrid amplifier. The hybrid amplifier includes a rare-earth doped fiber amplifier such as an EDFA (erbium-doped fiber amp), a Raman amplifier, a controller and a memory device. Noise is reduced by determining a gain balance between the EDFA and Raman amp that minimizes the noise figure. The controller performs a method that generates a plurality of functions relating the hybrid amp noise figure and the Raman gain for a particular span loss. These functions are then utilized to determine the Raman gain portion of the gain balance that minimizes the noise figure. The remaining portion of the gain balance is made up by the EDFA. For a hybrid amplifier that will see only one span loss value, then only one such function needs to be generated. Furthermore, the memory device of the hybrid amplifier can be programmed to store an optimum control curve that minimizes the noise figure for one or a plurality of span losses.

Abstract: In a method of amplitude equalization of a plurality of optical signals having mutually different wavelengths, the optical signals are launched into a first end of an optical fiber (5). The optical signals are amplified, before being launched into the fiber (5), to a level at which at least one of the signals exceeds a stimulated Brillouin scattering (SBS) threshold value (TSBS) characteristic of the fiber, so that part of the signal energy in the fiber is transferred to a Stokes signal propagating in the fiber (5) in a direction opposite to said optical signals. An apparatus for amplitude equalization of a plurality of optical signals having mutually different wavelengths comprises an optical fiber (5) having an input end (6) where said optical signals may be supplied to the fiber, and an output end (10) where said optical signals may be tapped from the fiber after equalization.

Abstract: The present invention aims at providing an optical amplifying apparatus constituted by combining Raman amplifiers, in which deterioration of a signal/noise ratio of output light is prevented to thereby improve the transmission characteristic of signal light, and an optical communication system utilizing such an optical amplifying apparatus. To this end, the optical amplifying apparatus according to the present invention comprises: first optical amplifying means for supplying excitation light to a Raman amplifying medium to thereby Raman amplify signal light; second optical amplifying means for amplifying the signal light output from the first optical amplifying means; and controlling means for controlling an operating state of the first optical amplifying means or the second optical amplifying means, so that a signal/noise ratio of the signal light to be output from the second optical amplifying means is kept substantially constant.

Abstract: A method of an apparatus for compensating optical non-linearity in optical devices and transmission systems. Two second order interactions are cascaded in phase-mismatched second harmonic generation to accumulate a non-linear phase shift of a fundamental wave. The non-linear phase shift can be set to provide a desired amount of non-linearity compensation. Compensation takes place in a compensating medium having a negative effective non-linear refractive index at the design operating conditions of the compensating medium. Compensators incorporating these principles may be incorporated as passive or active components in optical transmitters, repeaters or receivers. Active components may be tuned by varying the operating condition of the compensating medium, for example by controlling temperature or applied stress.

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 amplification apparatus for adjusting optical power of wavelength-multiplexed signal light at respective wavelengths and for adjusting the optical output power at the respective wavelengths and a deviation of the optical output power between the wavelengths. An optical power adjusting unit for receiving inputted light having signal light at a plurality of different wavelengths (&lgr;1, &lgr;2, &lgr;3, . . . , &lgr;N) multiplexed thereon, amplifying or attenuating light at least one wavelength included in the received light independently of light at different wavelengths from the wavelength of the light, is provided before or after an optical amplifier unit for amplifying the light having the signal light at the plurality of different wavelengths multiplexed thereon. Further, a control unit is provided for controlling the gain of amplification or attenuation performed by the optical power adjusting unit and the gain of amplification performed by the optical amplifier unit, respectively.

Abstract: Circuitry and a concomitant methodology for generating a burst support signal to augment an input bursty optical signal in an optical channel. The burst support signal is produced whenever the input bursty optical signal falls below a predetermined threshold. The burst support signal is the result of self-oscillation of a semiconductor optical amplifier and a tunable optical feedback loop. The wavelength of the self-oscillation is determined by the operating characteristic of the feedback loop.

Abstract: Optical amplifiers are provided in which optical gain is produced by Raman pumping fiber. The Raman-pumped fiber may be a span of transmission fiber or a coil of fiber in a discrete amplifier. Raman pump light may be provided using laser diodes operating at different wavelengths. The Raman pump light that is produced by the laser diodes may be modulated to reduce pump interactions in the fiber. Raman pump light may be modulated by directly modulating the laser diodes or by using optical components that modulate constant power pump light from the laser diodes.

Abstract: The present invention relates to a fiber optic amplifier comprising a structure enabling favorable signal amplification characteristics to be maintained even in an environment exposed to radiation. The fiber optic amplifier according to the present invention comprises a bleaching system for restoring glass defects generated within an optical fiber for amplification upon exposure to ultraviolet rays. This bleaching system carries out at least one of optical bleaching and thermal bleaching for the optical fiber for amplification. The optical bleaching is effected when bleaching light having a shorter wavelength shorter and a higher power than pumping light is supplied into the optical fiber for amplification, whereas the fiber optic amplifier has a structure which can introduce and eliminate the bleaching light.

Abstract: Regulated optical amplifiers for wavelength-division multiplex signal transmission that include a first control device for regulating the gain and a second, dominating control device having a significantly slower control behavior for regulating the output power level in conformity with a supplied rated power value. Both rapid level changes as well as slow changes in attenuation of the transmission path can be leveled with a transmission path utilizing these amplifiers.

Abstract: An optical transmission device that can be applied to a wavelength-multiplexed optical transmission system includes a first part creating a supervisory control signal to be transmitted in optical formation together with an optical main signal, the supervisory control signal comprising a vector of elements respectively corresponding to wavelengths. The device further includes a second part converting a vector included in a supervisory control signal received from a remote optical transmission device into another vector by a process using a path matrix in the vector received forms diagonal elements of the path matrix, the above another vector being transmitted to a next stage in the wavelength-multiplexed optical transmission system.

Abstract: A programmable amplifier 100 operable to independently adjust the amplification given to various optical signals passing through an optical fiber. An input optical fiber 102 provides a number of optical signals to a demultiplexer which separates each signal carried by the input fiber 102. Each individual wavelength travels to a variable attenuator 106 which lowers the signal strength of each signal based on an input from the system controller 108. The attenuated signals are combined by multiplexer 112 and input to an optical amplifier 114. The optical amplifier 114 receives the combined signal and amplifies each signal in the combined DWDM signal across the entire bandwidth of the amplifier 114. The amplified signals are input to a splitter 116 which removes a small portion of the entire spectrum output by the amplifier 114. The remaining portion of the signal passes to an output fiber 110 and travels to the remainder of the optical network.

Abstract: The present invention provides a hybrid Raman/EDFA optical amplifier that utilizes a first optical detector that generates a first electrical or electronic signal that is proportional the combined optical power of the signal light and the leaked pump laser light, a second optical detector that generates a second electrical or electronic signal that is proportional to the power of the pump laser light and an electronic subtraction circuit that receives the first and second electrical or electronic signals and generates a difference signal that is proportional to only to the optical power of the signal light and insensitive to the power of the Raman pump laser light. The difference signal is utilized by an EDFA control circuit to control and/or adjust the operation of the EDFA based upon changes in the power of the input optical signal.

Abstract: A performance monitoring method for an optically amplified transmission system. The method provides the optical power at each amplifier site, taking into account the inaccuracies introduced by the SRS in the power estimation obtained with the current methods. An optical spectrum analyzer is used at the output of the transmission link of interest to accurately measure the output power of each wavelength. This value is sent upstream to the last amplifier in the link, to compute an error term as the difference between the actual measurement and the estimation. The error term is used to infer the SRS-induced error by system elements not accounted for in the model. The error term is then fed-back to each amplifier in the link, so that the estimated power is adjusted to account for the SRS-induced inaccuracy.

Abstract: An optical brancher 110 branches an input optical signal into two. An optical detector 120 converts one optical signal branched by t e 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: A dynamic slope compensation filter (DSCF) provides dynamic gain slope modification for an optical amplifier. The optical amplifier provides amplification for a plurality of wavelengths within an amplification band. The filter includes an optical waveguide core, an optical waveguide cladding and an optical waveguide overcladding. The optical waveguide core guides a plurality of wavelengths. The core has a core refractive index and includes at least one coupler that functions to couple at least a portion of the plurality of wavelengths from the core to the cladding. The optical waveguide cladding surrounds the core and has a cladding refractive index that is less than the core refractive index. The optical waveguide overcladding surrounds at least a portion of the cladding and has a variable overcladding refractive index that is adjustable within a range that is less than and greater than the cladding refractive index.

Abstract: This invention describes an apparatus and method for a self adjusting Raman amplifier for fiber optic transmission lines incorporating a line diagnostic mechanism in order to calculate, control and optimize the operating parameters for the amplifier. This need arises because the amplifier gain medium is the transmission line itself and the amplifier properties depend on the optical fiber properties along the first tens of kilometers of the transmission line from the pump. A Line Analyzing Unit, adjacent to the Raman pump unit, operates before the Raman pump is enabled and during operation, and characterizes the transmission line. The Line Analyzing Unit determines and characterizes the types of optical fibers installed along the transmission line and calculates and optimizes the pump or pumps power in order to achieve optimum gain and gain equalization.

Abstract: An optical communication system which includes a transmission path through which a light is transmitted to a specific point, such as to a receiver. The transmission path includes a plurality of sections so that the light travels through the sections to the specific point. Each section overcompensates for dispersion produced in the respective section for the light so that an amount of dispersion for the light at the specific point is substantially zero.

Abstract: An intermediate optical amplifier stage of an optical amplifier having cascaded amplifier stages includes an optical circulator having a first port forwardly coupled with a second port which is forwardly coupled with a third port, wherein the second port is optically coupled with an orthogonal polarisation state converting reflector via a length of optically pumped optically amplifying optical fibre. The orthogonal polarisation state converting reflector may be constituted by the series combination of a collimating lens, a Faraday rotator that provides a &pgr;/4 plane of polarisation rotation in respect of a single transit of light through the rotator, and a mirror.