Abstract: A system and method for improving optical signal gain efficiencies of semiconductor optical amplifier devices. The system and method exploits a wavelength-locked loop servo-control circuit and methodology that enables real time mutual alignment of the center wavelength of an optical signal having a peaked spectrum function and transmitted through the semiconductor optical amplifier, and a center wavelength of a wavelength selective device such as an optical filter implementing a peaked passband function in an optical system. The wavelength-locked loop servo-control circuit and methodology may be further exploited to control various types of modulation applied to the optical signals transmitted in optical systems.

Abstract: An optical sending apparatus of this invention includes a plurality of optical signal generating sections, a dispersion compensating section and a wavelength multiplexing section. The dispersion compensating section performs compensation with a predetermined chromatic dispersion value to at least one of polarized light generated by the optical signal generating sections while a predetermined state of polarized light is maintained. The wavelength multiplexing section combines output light outputted from the optical signal generating section with output light passing through the dispersion compensating section so that the polarized light of adjacent wavelengths crosses orthogonal to each other. The optical sending apparatus having such a construction can generate high-density WDM optical signals, the dispersion of which is compensated in advance, by a polarization crossing method.

Abstract: A method and apparatus are provided for increasing the energy of chirped laser pulses to an output in the range 0.001 to over 10 millijoules at a repetition rate 0.010 to 100 kHz by using a two stage optical parametric amplifier utilizing a bulk nonlinear crystal wherein the pump and signal beam size can be independently adjusted in each stage.

Abstract: The invention concerns a method and apparatus for determining noise power caused by amplified spontaneous emission in a signal output by an optical amplifier (100). The amplifier is connected downstream of further optical amplifiers or components that generates noise power due to amplified spontaneous emission (ASE). The amplifier is connected to a control channel and receives via this channel information about the proportion of ASE power contained in the amplifier input signal. The amplifier further includes a control unit for calculating the ASE power generated in the amplifier, for example using a predetermined relationship between the gain of an amplifier and the generated amplified spontaneous emission (ASE). The ASE power in the amplifier output signal is then determined as the sum of the generated ASE power and the power resulting from propagated ASE. The determined target output power can be used to stabilise the amplifier output.

Abstract: Early warning failure detetection is provided for an optical amplifier. The optical amplifier is based on a lasing semiconductor optical amplifier, which generates a ballast laser signal in addition to the amplified optical signal. The ballast laser signal exhibits a wavelength shift before failure and this wavelength shift is used as the basis for an early warning of future failure of the amplifier.

Abstract: A multi-pass optical amplifier system is provided comprising an amplifier medium (20) and at least one relay imaging telescope (18, 24) for imaging light from the amplifier medium onto a primary light directing optical component, such as a mirror (26, 29) and for imaging light directed back from a primary light directing optical component (26, 28) into the amplifier medium so that light is re-passed through the amplifier medium. The system further includes a phase conjugate mirror arrangement for intercepting light between passes for the amplifier medium to generate a phase conjugate reflection of the light incident on it. Preferably, the system is arranged such that a light beam is incident on phase conjugate mirror (22), after having passed through the amplifier medium a predetermined number of times and the phase conjugate reflection retraces the path of the incident beam.

Abstract: The invention provides improved methods and systems for a precise and selective cross-talk cancellation and pilot tones deletion in optical amplifiers. The method for cancellation of cross-talk among multiple channels occurring in a traditional optical amplifier comprises: detecting tones at an input and an output of a Smart Optical Amplifier that includes a traditional optical amplifier and a Cross-talk Cancellation Unit; comparing the detected tones at the input and output of the Smart Optical Amplifier; generating destructive tones with such amplitudes and phases so as to cancel cross-talk; and eradicating cross-talk at the output of the Smart Optical Amplifier by applying the destructive tones in the Cross-talk Cancellation Unit. Eight different embodiments that correspond to different combinations of traditional optical amplifier types and the type of technology (analog or digital) used in processing and control of signals are described.

Abstract: Optical network equipment is provided. The optical network equipment may include equipment with optical gain stages such as optical amplifiers. The equipment may be used in fiber-optic communications links in communications networks. The gain stages may be based on optically-pumped rare-earth-doped fiber. The equipment may include optical monitors that are used to measure the power of optical data signals propagating through the equipment. A control unit in the equipment may be used to analyze the optical data signal power measurements. The results of the analysis may allow the control unit to determine whether the amplifier output power is affected by gain transients or drift effects. Gain transients may be suppressed by making pump power adjustments. The control unit may compensate for the effects of drift by making pump power adjustments or by adjusting components such as variable optical attenuators or dynamic filters.

Abstract: Control information is embedded in the signal passing through an optical amplifier by varying the power level of that amplifier's pumped laser source. Connection discovery for a given optical port can then be performed by detecting variations in the optical signal present on that given port and then attempting to match these with the variations assigned to each of the optical amplifiers. If a match is found, then the optical amplifier connected to the given port can be identified. As a result, the need to physically handle the fiber in order to effect connection discovery is eliminated, rendering the process faster, safer and more reliable. Also, the present invention advantageously allows a connection discovery function to be invoked from a remote location.

Abstract: An amplifying module 101 for an optical network has a fiber amplifier 102 for amplifying a multiplexed optical stream having a plurality of wavelength channels. The fiber amplifier 102 has a set point gain. The module 101 has module control means 108 for controlling the operating conditions of the fiber amplifier 102 and supplying means for supplying to the module control means 108 information representative of the channel loading condition. In response to the information, the module control means 108 adjusts the operating conditions of the fiber amplifier 102 such that the fiber amplifier gain does not exceed an acceptable deviation limit away from a set point gain.

Abstract: A return-to-zero pulse optical communication system includes fast saturable absorber means (F1,DSF) to provide substantially zero average dispersion in a single amplifier span (SIF,DSF) to reduce the effect of timing jitter an provide considerably enhanced propagation distances.

Abstract: A temperature-stabilized optical amplifier (100) comprises at least an erbium-doped waveguide (101) for amplifying optical signals; at least a first and a second pump sources (103, 104) for generating respective pump beams at a first and, respectively, a second pump wavelength (&lgr;1, &lgr;2), said first and second pump wavelength being lower and, respectively, higher than 978 nm at an intermediate temperature of a predetermined range of temperature, and being subjected to drift as a consequence of temperature variations; and a pump distribution device (105), optically coupled to said pump sources for receiving said pump beams, and optically coupled to said at least an erbium-doped waveguide for feeding to said at least an erbium-doped waveguide a mixed pump radiation comprising at least a power fraction of each of said pump beams.

Abstract: An optical amplifier is implemented which can reduce its size and cost by using a smaller number of components. Signal light coupled by an optical combiner with pump light fed from a pumping light source is incident on an EDF (erbium-doped fiber) to be pumped and amplified by the pump light, is emitted from the EDF to be incident on a second optical circulator and output from its second port, passes through an optical component to be fed back to the second optical circulator and launched into the EDF from the second optical circulator, passes through the EDF again in the direction opposite to the first passing direction followed by passing through the optical combiner, and is output from the third port of a first optical circulator.

Abstract: A multireflector fiber optic filter apparatus, wherein the transmittance and reflectance spectra are periodic in frequency, the apparatus comprising an etalon with N equally spaced reflectors wherein the transmittance and reflectance spectra of said etalon are periodic in optical frequency with a period given by the formula: &Dgr;&ngr;FSR=c/(2ngL), where c=the free space speed of light; ng=the group refractive index for the light propagating in the medium between the reflectors, L=separation between said reflectors, and N is an integer=3,4,5, . . . In a further aspect, an optical circulator is connected to the etalon and an optical fiber is connected to the optical circulator for reflected output.

Abstract: In a method of compensating polarization dependent loss (PDL) in a wave division multiplex (WDM) optical communications system, a performance parameter is monitored at a predetermined monitoring point. The performance parameter is indicative of respective channel PDL for each one of a plurality of channels of the optical communications system. A error function is calculated as a function of wavelength across a wavelength spectrum of interest, using the measured performance parameter values. Finally, a broadband PDL compensator is controlled based on the calculated error function.

Abstract: The present invention is an arrangement for utilizing optical information sent through an optical network from a sending site to at least one receiving site. An optical parametric amplifier OPA receives the optical information sent at a set of input wavelengths. A mixer amplifier mixes the input wavelengths with an optical pump wavelength. A set of optical conjugate copy wavelengths are generated from the set of input wavelengths. A WDM-splitter separates the set of input wavelengths from the set of conjugate copy wavelengths. The set of input wavelengths and/or the set of conjugate copy wavelengths are forwarded individually to the at least one of the receiving site.

Abstract: An optical amplifier is provided from a body 21, at least part 25 of which is doped with a rare earth such as erbium. At least one waveguide 47 extends through the doped part of the body. Pump light 51 is input on a side face 35 of the body and is distributed in the body over the length of the waveguide 47. A reflective coating 57 may be provided away from the pump light input, including on the opposite face 37 to the pump light input, to multiply reflect pump light within the body 21 to distribute the pump light within the body. The body may be in the form of a slab.

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

Abstract: An object of the invention is to easily realize an optical element using an etalon type structure, capable of changing a periodic transmission wavelength characteristic in an axial direction of transmissivity, and also capable of changing a periodic characteristic with respect to wavelength. To this end, a transmission wavelength characteristics variable optical element according to the invention comprises: a light interference section including a pair of wedge shape magneto-optic crystals arranged with taper faces thereof in close contact, that can change a distance between reflecting films formed on parallel planes of the magneto-optic crystals, by relatively moving the magneto-optic crystals by movable sections, permanent magnets for applying a fixed magnet field to the pair of magneto-optic crystals, an electromagnet for applying a variable magnetic field in a direction different to the fixed magnetic field, and a variable current source controlling the current flowing into the electromagnet.

Abstract: Four-wave mixing crosstalk between co-propagating Raman amplification pump sources and WDM channels is suppressed. Therefore, co-propagating pumping may be applied to Raman amplification without incurring penalties due to four-wave mixing crosstalk. Pump power need not be substantially increased to accommodate use of the present invention. Also, the use of lower cost Fabry-Perot pump sources is facilitated. In one implementation, the advantageous suppression of four-wave mixing crosstalk between pump signals and WDM channels is accomplished by imposing chromatic dispersion on the co-propagating pump sources.

Abstract: An optical output signal of an optical amplifier 1 branched by an optical divider/splitter 2 is separated by an optical demultiplexor 3 into different paths □1 to □n in accordance with the wavelength, and the level of each different wavelength component is adjusted under the control of an optical attenuator control circuit 9 on the basis of a transmission wavelength information notified through a transmission wavelength information input terminal 14. At this time, in the path corresponding to the wavelength transmitted, the attenuation amount of an optical attenuator is controlled to a minimum level, and in the path corresponding to the wavelength other than the wavelength transmitted, the attenuation amount of an optical attenuator is controlled to a maximum level. After the level adjustment, the different wavelength components are combined by an optical multiplexor 5, and the level of the combined signal is detected by a photo diode 6.

Abstract: A system and method for amplifying an optical signal within an optical waveguide amplifier including providing at least one optical waveguide amplifier having an input for receiving an optical source signal therein and an output, wherein a forward pumping direction extends from the input to the output and rearward pumping direction extends from the output to the input. The system also includes providing at least one excitation light source in optical communication with the optical waveguide amplifier and capable of generating at least one excitation light. The system further includes amplifying the source signal by pumping a first excitation light from the excitation light source in the rearward pumping direction, and amplifying the source signal by simultaneously pumping a second excitation light from the excitation light source in the forward direction.

Abstract: Optical signal interleaver/deinterleavers with reduced chromatic dispersion are described. In one embodiment, the interleaver/deinterleavers include two optical filters and an optical isolator coupled to receive the output of each of the optical filters. The optical isolators feed the filtered signals back to the filters. Passing the filtered signals back through the filters in the opposite direction as the first pass allows the filters to cancel, or nearly cancel, the chromatic dispersion caused by the filters on the first pass. Thus, the interleaver/deinterleavers provide reduced chromatic dispersion as compared to use of a single filter or of cascaded filters.

Abstract: A planar waveguide module has integrally formed thereon a waveguide and, in sequence along the optical transmission path, a first LOA, a 90° polarisation rotator, a VOA and a second LOA. The LOAs and are gain-clamped SOAs having linear gain responses over the required wavelength range. In the absence of the polarisation rotator the PDGs of the LOAs would be added together to provide an overall PDG of approximately twice the PDG of a single LOA. However the inclusion of the polarisation rotator between the LOAs causes a substantial reduction in the overall PDG. If TE polarised light is supplied to the first LOA, the polarisation rotator will cause TM polarised light to be supplied to LOA, and accordingly the overall gain of the module will equal Gain(TE, LOA 3)+Gain(TM, LOA 7)−attenuation.

Abstract: An active optical amplifier in which a unitary optical amplifier constructed from a unitary optically transparent chip that has been doped so as to be optically active, amplifies incoming signal photons when excited by a pump laser of sufficient energy. The unitary optical amplifier receives input photons and pump laser energy and provides output photons that have the same spatial orientation and phase as the corresponding input photons. A laser direction and ranging (LADAR) may be constructed from the active optical amplifier by further including first imaging optics to focus the input photons onto the surface of the unitary optical amplifier and second imaging optics to focus the output photons from the active unitary optical amplifier onto a focal plane image sensor array. The electronic signals from the focal plane image sensor array may then be displayed on a conventional display.

Abstract: An advantageous amplification architecture for DWDM systems including systems with very high capacity is provided. A modular interleaved structure for amplification is provided. Advantages include robustness to non-linear effects, modular as-needed deployment of system capacity, and low noise figure in implementations that incorporate Raman amplification technology.

Abstract: A method and apparatus to enable the use of low cost high RIN optical sources for microwave photonic links by combining the wide-gain bandwidth and low cost of an EDFA, with the narrow gain bandwidth of a Brillouin amplifier. The hybrid Brillouin/EDFA (“hybrid amplifier”) apparatus of the present invention includes at least two couplers, a phase modulator, an Erbium-doped fiber, a laser source to pump the Erbium fiber, an optical circulator, and a length of fiber used for Brillouin amplification. Optical signals from the laser source are split into two optical paths by a polarization maintaining coupler. Optical signals passing through a first path are amplified by the Erbium doped fiber, and the amplified signals are passed through the optical circulator before sending the optical signals into one end of a spool of fiber in order to pump the Brillouin acoustic wave.

Abstract: Optical amplification systems and methods are disclosed. A first optical amplification system includes an optical interface filter configured to separate a desired communications band from at least one other communications band, and an optical amplifier in communication with the interface filter for amplifying the desired communications band. The optical amplifier includes at least one suppression filter configured to attenuate a wavelength subset of the at least one other communications band nearest the desired communications band and narrower than the at least one other communications band.

Abstract: A mode matching gain element for an optical system is described, that supports a single mode of the optical signal, and that matches the incoming wavefront to a required outgoing wavefront. The incoming wavefront is passed through a phase conjugating structure, and the mode of the gain element is matched to the mode of the input and output optic fibers. The phase conjugating structure includes lenses or mirrors which time-reverse the incoming signal.

Abstract: Optical transmission systems of the present invention include at least one optical amplifier configured to provide optical amplification of one or more information carrying optical signal wavelengths. At least one optical amplifier is controlled based on an in situ performance characterization of the at least one optical amplifier and the transmission fiber. The in situ, or installed, performance characteristics of the optical amplifier can be characterized based on relative gain measurements over the signal wavelength range as a function of the supplied pump power. The installed characterization allows the optical amplifier performance and gain profiles to be tightly controlled over the signal wavelength range in the transmission system.

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

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

Abstract: In a method and apparatus for tracking dynamic characteristics of an optical amplifier, optical signal probes are used to determine the gain and the corner frequency of the optical amplifier. A first optical probe having a predetermined modulation frequency above an expected corner frequency of the amplifier is used to estimate the gain of the optical amplifier. A second optical probe signal having a second predetermined modulation frequency at or below the expected corner frequency of the amplifier is used to estimate the corner frequency. These parameters can be used to optimize gain control of an optical amplifier.

Abstract: A variable optical attenuation system has at least one variable optical attenuation device that receives a light signal, attenuates the light signal, and transmits an attenuated light signal. The variable optical attenuator system further has a controller circuit in communication with the variable optical attenuation device to provide an attenuation control signal to the variable optical attenuation device to cause the variable optical attenuation device to adjust an attenuation factor of the variable optical attenuation device. The variable optical attenuator system also has a data retaining device such as an EEPROM in communication with the controller circuit. The data retaining device has a listing of attenuation factors and corresponding attenuation control signals. A communication interface such as a serial data link, within the variable optical attenuator system provides communication between the controller circuit and an external command system.

Abstract: An optical fiber amplifier having improved gain and reduced noise, and an optical amplifier which restrains an unnecessary polarization component in the signal output light, maintains polarization of a signal light and performs optical amplification in which a polarizer is connected between a first optical fiber and a second optical fiber. An amplified spontaneous emission is emitted from the output end of the first fiber with the amplified signal light and is incident to the polarizer. The polarizer is disposed so as to transmit a polarization component which is parallel with the signal light. Among the different light components which are incident to the polarizer, a light having a polarization component which is orthogonal with the signal light is rejected.

Abstract: It is an object of the invention to provide a level-flattening circuit for WDM optical signals which can be used in an optical signal repeating station. A level flattening circuit for WDM optical signals is supplied with WDM optical signal and demultiplexs them into individual optical signals having different wavelengths, levels of which are separately feedback controlled to provide flattened optical signal levels.

Abstract: In method of controlling an optical amplifier dynamically adapts to both configuration and performance changes of a communications system. An error vector is calculated to indicate a difference between respective detected values and target values of a parameter of a light beam downstream of the optical amplifier. A sensitivity matrix indicative of a sensitivity of the detected parameter value to incremental changes in a control variable of the optical amplifier is calculated. A predicted optimum value of the control variable is then calculated using the error vector and the sensitivity matrix. Calculation of the predicted optimum control variable value can be iterative, with the sensitivity matrix calculated either during each iteration, or at the beginning of each optimization run. As a result, optimization of the amplifier control variables is performed based on a sensitivity matrix that accurately reflects the performance of the amplifier.

Abstract: A controlling apparatus and a controlling method for a wavelength division multiplexing optical amplifier to reduce the controlling error due to noise light included in the monitoring light. The controlling apparatus branches, by a photocoupler, a portion of WDM signal light amplified by a light level controlling part and separates the branched light into groups of even-numbered channel components and odd-numbered channel components using a wavelength channel separate filter. Monitor signals corresponding to the light powers of the even-numbered group and odd-numbered group, respectively, are generated by respective photoelectric converting parts and LPF's. One of the monitor signals, which corresponds to one of the even-numbered group and the odd-numbered group, is selected by a monitor signal selecting/controlling part and then sent to a comparator.

Abstract: Optical transmission systems of the present invention include at least one optical amplifier configured to provide optical amplification of one or more information carrying optical signal wavelengths. At least one optical amplifier is controlled based on an in situ performance characterization of the at least one optical amplifier and the transmission fiber. The in situ, or installed, performance characteristics of the optical amplifier can be characterized based on relative gain measurements over the signal wavelength range as a function of the supplied pump power. The installed characterization allows the optical amplifier performance and gain profiles to be tightly controlled over the signal wavelength range in the transmission system.

Abstract: Control information is embedded in the signal passing through an optical amplifier by varying the power level of that amplifier's pumped laser source. Connection discovery for a given optical port can then be performed by detecting variations in the optical signal present on that given port and then attempting to match these with the variations assigned to each of the optical amplifiers. If a match is found, then the optical amplifier connected to the given port can be identified. As a result, the need to physically handle the fiber in order to effect connection discovery is eliminated, rendering the process faster, safer and more reliable. Also, the present invention advantageously allows a connection discovery function to be invoked from a remote location.

Abstract: An optical amplifier site comprising: (i) a distributed Raman amplifier providing a first signal gain level; (ii) an optical amplifier located downstream from the distributed Raman amplifier, the optical amplifier being indirectly coupled to the distributed Raman amplifier, the optical amplifier including a first amplification medium, providing a second signal gain level; (iii) at least one optical signal loss element located between the distributed Raman amplifier and the optical amplifier and, contributing at least 0.5 dB optical loss to the amplifier site; (iv) a second amplification medium located down-stream from the first amplification medium; and (v) at least another one optical signal loss element, this at least another one optical signal loss element being located between said first amplification medium and said second amplification medium.

Abstract: Optical amplifiers and other optical network equipment for handling optical data signals in fiber-optic communications links are provided. Optical fiber that is pumped by laser diode pumps is used to provide optical gain. The laser diode pumps may be based on laser diode devices that do not have temperature controllers and integral back facet monitors. A control unit may be used to keep track of the age of the laser diode pumps. Information on the age of the pumps may be used to determine the maximum allowable drive current for driving the pumps. Information on the age of the pumps may also be used to select an appropriate drive current level during operation of the pumps.

Abstract: The invention is directed to an optical fiber amplifier having a switchable or interchangeable fiber module for varying the effective length of an amplification fiber. An optical fiber amplifier for wavelength-division multiplex (WDM) signals comprises an interchangeable fiber module (FM) in the basic amplifier module (VM) for matching the gain to different input levels for optimum noise behavior. The change in amplification is based on the variation of the length of the amplification fibers (EDF1, EDF2).

Abstract: A control method and apparatus used for a bias controller of automatic bias correction on an optical modulator of optical emitter of external modulation type is a close-loop control system, composed of a base signal generator, an optical receiver, a second-order harmonic signal generator, a second-order harmonic signal detector, a DC amplifier, and a temperature automatic correction device. The bias voltage point of the optical modulator can remain a constant, whereby the optical power can be exported in stable level and distortion of transmission is reduced. It can be avoided about the effect of the environmental temperature, resulting in the change of optical output and the additional signal distortion of the transmission signal.

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

Abstract: An optical amplifier includes an optical amplification medium which has simultaneous inputs of a WDM signal light and a pumping light and amplifies the WDM signal light, a pumping light source, and an amplification characteristic supervisor part which evaluates the gain tilt of amplified WDM signal lights. The supervisor part is provided in advance with a record of the relation between the medium output light power and the pumping light power corresponding to the output light power in terms of a number of proper curves plotted for certain gain tilts, and adapted to select a proper curve which is nearest to the relation in operation between the power of the pumping light which is incident to the medium in operation and the resulting amplified output light power from among the recorded proper curves, thereby determining the gain tilt of the medium based on the selected proper curve.

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: The present invention relates to a detection of a cutoff condition of an optical fiber. An optical transmission system includes an optical amplifier, an optical/electrical converter, a dispersion compensator or polarization dispersion compensator. An optical amplifying unit is made up of a former-stage optical amplifier for amplifying and outputting an optical signal inputted thereto, a latter-stage optical amplifier for handling the amplified optical signal from the former-stage optical amplifier and a latter-stage input level detecting section for detecting a latter-stage input level representative of an input level of the optical signal inputted thereto; and a control section for controlling an output level from the optical amplifying section based on the latter-stage input level and a reference latter-stage input level. This configuration enables detecting an off-condition of a fiber with a simple circuit and optical parts already existing therein without suppressing an output level of an optical signal.

Abstract: Designs and techniques for actively stabilizing optical cavities in devices such as fiber lasers with reduced power consumption in the active control.

Abstract: The present invention aims at providing a controlling apparatus and a controlling method for a wavelength division multiplexing optical amplifier to reduce the controlling error due to the affection of noise light included in the monitoring light to be used for controlling the wavelength division multiplexing optical amplifier, to thereby realize precise controlling of the optical amplifier. To this end, the controlling apparatus for a wavelength division multiplexing optical amplifier according to the present invention: branches, by a photocoupler, a portion of WDM signal light amplified by a light level controlling part; and separates the thus branched light into groups of even-numbered channel components and odd-numbered channel components making use of a wavelength channel separate filter. Further, monitor signals corresponding to the light powers of the even-numbered group and odd-numbered group, respectively, are generated by respective photoelectric converting parts and LPF's.