Abstract: A laser transmitter capable of transmitting large numbers of WDM channels but requiring locking of only a single channel. Each of the channels can be individually modulated using an external modulator.

Abstract: The present invention provides an all-optical dynamic gain equalizer of an open-loop design using nonlinear optical materials for equalizing channel power without the need of complex electronics and close-loop control, and provides pulse reshaping and in some embodiments noise reduction at no extra cost. The invention achieves restoration of spectral power uniformity by employing nonlinear optical limiters with desirable power transfer function curves to each of the optical signals to be equalized. The invention provides the highly desirable functions of dynamic gain equalization, and optical pulse reshaping. Some embodiments constructed according to the invention provide signal dynamic range control by biasing the nonlinear optical limiter with a biasing optical signal.

Abstract: The present invention discloses a wide band optical amplifier with a common mid-stage device. In the wide band optical amplifier according to the present invention, the signals that enter the amplifier are first split into a couple of sub-band signals. The sub-band signals are amplified independently at different optical amplification sections, but they share a common mid-stage device, which reduces the complexity and the cost of the amplifier. The sub-band signals propagate count-directionally in the common mid-stages device to reduce the nonlinear interactions between the signals in different sub-bands. A wide band optical amplifier incorporating a common mid-stage device with directionality is also disclosed.

Abstract: A fiber optic phased array, as well as associated methods and apparatus for controllably adjusting the frequency of the optical signals emitted by a fiber optic phased array, are provided that permit wide band phase control and may be implemented utilizing conventional analog electronics. In this regard, the method and apparatus can independently control the phase of the optical signals propagating through each fiber optic amplifier of the fiber optic phased array, even as large optical phase disturbances occur. As such, the control method and apparatus permit a fiber optic phased array to generate a flat phase front that, in turn, can provide a diffraction limited output laser beam. Alternatively, the control method and apparatus may be designed such that the output signals emitted by an array of fiber optic amplifiers has any other desired phase front, such as to compensate for atmospheric perturbations or the like.

Abstract: An optical amplifier, or optical repeater, for amplifying wavelength division multiplexed (WDM) light A first demultiplexer demultiplexes the WDM light into first and second lights corresponding to different wavelengths in the WDM light. First and second optical amplifiers amplify the first and second lights, respectively. A first multiplexer multiplexes the amplified first and second lights into a multiplexed light. A dispersion compensator compensates for dispersion in the multiplexed light. A second demultiplexer demultiplexes the dispersion compensated, multiplexed light into the first and second lights. Third and fourth optical amplifiers amplify the demultiplexed first and second lights, respectively. A second multiplexer multiplexes the amplified first and second lights from the third and fourth optical amplifiers into a WDM light. The optical amplifier can be configured so that the first and second lights travel through the dispersion compensator in opposite directions.

Abstract: A low noise optical amplifier used in an optical communication system includes optical amplifying elements for amplifying optical signals of a specific wavelength(&lgr;) incident from their ends(F1,F2) and endowing phase difference between ASEs, optical diverging means to interfere the amplified optical signals and the ASEs output from both ends(F1,F2), first path of length(L1) to optically connect the one end(F1) to first gate(D1) of the optical diverging means, and second path of length(L2) to optically connect the other end(F2) to second gate(D2) of the optical diverging means. The first and second paths are designed with distance(L1-L2) so that the amplified optical signal causes reinforcing interference at the third gate(D3) and destructive interference at the fourth gate(D4), and the ASE causes destructive interference at the third gate(D3) and reinforcing interference at fourth gate(D4).

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: The present invention concerns an apparatus for combining light from at least two laser light sources, preferably in the context of confocal scanning microscopy, and in order to make laser light sources of low output power usable as light sources, in particular for confocal scanning microscopy, is characterized in that the light from the laser light sources has at least approximately the same wavelength; and that at least one beam combining unit that combines the light beams in at least largely lossless fashion is provided.

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: An object of the present invention is to provide a separating apparatus having a simple configuration, capable of time division separating time division multiplexed signal light directly and stably.

Abstract: An optical communication system includes a plurality of optical channels, each of which passes a single optical wavelength signal. Each of the plurality of optical channels includes an optical amplifier which is controlled to operate at a predetermined output power level independent of channel wavelength and input power level by operating each optical amplifier in a saturation mode. Pumping power for operating each optical amplifier in the saturation mode is supplied from shared optical pumps or a plurality of one per channel optical pumps.

Abstract: An image display apparatus comprises a hologram screen 2 formed by bonding a hologram element 20 to light-transmissible films 21 and an illumination device 11 for irradiating image light 10 onto the hologram screen and reproducing an image on the hologram screen 2. The light-transmissible film 21 positioned on the irradiation side of the image light 10 relative to the hologram element 20 has an angle deviation of not greater than 45 degrees between a direction of the light-transmissible film 21 that gives the highest thermal shrinkage ratio and an axial direction in the hologram screen 2. Therefore, the image display apparatus can provide high-quality images without the superposition of an interference pattern on the images on the hologram screen.

Abstract: The present invention relates to an apparatus for optical coherence reflectometry, in particular for optical coherence tomography, wherein the apparatus for optical coherence reflectometry comprises a wavelength scanning laser source for providing a light signal, and splitting means for dividing said light signal into a sample light field and a reference light field, wherein the sample light field is directed to the sample being measured, and the light reflected from the sample is amplified without correspondingly amplifying the light reflected in the reference light field. Thereby, it is possible to direct substantially all light energy from the first reflected light field to the detectors, and to obtain fully the utilisation of the amplification of the first reflected light field. The optical amplifier inserted in the sample reflected light field is different from the source so that the effect of the light source may be regulated independent of the degree of amplification.

Abstract: An interferometer that includes a first beam-splitting surface positioned to separate an input beam into a first beam and a second beam. A first set of optics is positioned to receive the first beam, direct it to contact a first reflector multiple times and produce a first intermediate beam. The first intermediate beam follows a nominal output path when the first reflector has a first alignment normal to the first beam prior to reflection by the first reflector. The first set of optics includes a second beam-splitting surface, a third beam-splitting surface, and a first fold optic that are positioned to reduce displacement of the first intermediate beam from the nominal output path when the first reflector has an alignment different from the first alignment.

Abstract: An external-resonator laser system having multiple laser elements is configured to permit each laser to undergo individual amplification notwithstanding optical beam combination. In this way, overall output power may be scaled in a desired fashion, depending on the selected characteristics of the optical amplifier elements. To achieve additional power, each of the amplifiers may implemented as a phased array. Viewed more generally, a phased-array configuration affords beam combining in two stages, with each contributing input source itself composed of multiple sources whose outputs have been combined. If each phased-array source emits at a different wavelength, this design offers a multi-wavelength output whose power level may be scaled in accordance with the number and character of the devices forming each phased array.

Abstract: An amplification architecture for WDM receiver systems. The WDM channel grid is divided into groups of adjacent channels. A separate optical amplifier is provided for each channel with a single pump being shared among the channels of each group. The gain experienced by channels of a given group may be adjusted by varying the power of the group's pump. This approach allows equalization of received channel power such that all channels fall within the desired dynamic range. The amplification architecture may be implemented in a space-efficient manner at low cost.

Abstract: A method of broadband amplification divides an optical signal of wavelength of 1430 nm to 1620 nm at a preselected wavelength into a first beam and a second beam. The first beam is directed to at least one optical amplifier and produces an amplified first beam. The second beam is directed to at least one rare earth doped fiber amplifier to produce an amplified second beam. The first and second amplified beams are combined.

Abstract: An optical amplifier with improved output power utilizing less optical fiber components and reduced noise is disclosed. A first optical fiber amplifier is pumped by a first light source prior to splitting into a number of sub-bands, and a second optical fiber amplifier is pumped by a second light source. One of the sub-bands is amplified in multiple stages using a reflector, by passing the amplified sub-band back into the second optical amplifier in a reverse direction. Thereafter, all amplified sub-band signals are recombined to produce an output signal.

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

Abstract: An optical amplifier for two adjacent bands of optical data channels provides gain across the entire spectrum, including the so-called dead-band, by splitting the entire input signal equally into two paths. One path is optimized to amplify one band and the other path is optimized to amplify the other. An optical delay in one path, usually the one optimized for the lower wavelength band, ensures equal optical path lengths for the two paths. The amplified signals in that two paths are then combined to yield or flat gain profile across the two bands and the gap in-between.

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: The present invention provides tunable optical system, and a method for forming the same, that exhibits a broader tuning range with fewer components than prior art tunable optical systems. The tunable optical system of the present invention includes a plurality of wavelength routers, each having a different optical channel resolution, optically coupled to a plurality of optical amplifier arrays. The free spectral range of each of the second and subsequent wavelength routers is equal to a total bandwidth of one of its respective grating orders. The system is tuned by selectively activating optical amplifiers in each of the optical amplifier arrays. The tunable optical system of the present invention can be used to make tunable semiconductor emitters, receivers and filters.

Abstract: An optical amplifier arrangement comprises a splitter for providing an input WDM optical signal on at least first and second output paths. An optical amplifier is provided in at least one of the paths, and a signal routing arrangement is provided for routing individual channels or groups of channels of the WDM signal within the at least one of the paths. A switch selects the signal from one of the at least first and second output paths. In this arrangement, there are two paths between the input and output. Whilst one path is being used, the components in the other path can be upgraded. For example, a switching arrangement may be provided in the other path, and an amplifier may also be upgraded, without disrupting service in the path in use. This enables an amplifying node within an optical communications system to be incrementally upgraded.

Abstract: An optical amplifier for amplifying the channel signals of a WDM signal comprises an amplifier arrangement for amplifying a band of the channels. The amplifier arrangement comprises an amplifier (6) and a filter (8). The filter comprises a controllable optical filter having an attenuation characteristic which comprises a region of positive gradient and a region of negative gradient with respect to input frequency. The magnitude and alignment along the frequency axis of the attenuation characteristic is variable, such that the filter can be tuned to provide gain flattening for the amplified band of channels. The filter can be tuned to the requirements of a particular sub-band, whilst identical filters can be used for each sub-band. This invention enables identical filters to be used, and gives good pump power efficiency, as the attenuation of each filter can be controlled to the desired level, thereby avoiding the need for large increases in pump power.

Abstract: The proposed amplifier structure and associated method of optical signal amplification efficiently utilizes the limited length of rare earth-doped optical amplifier. A multi-stage of amplification stages, which includes a first erbium-doped fiber amplifier stage pumped by a first pump light source and a second erbium-doped fiber amplifier stage pumped by a second pump light source, is provided and includes a split section disposed between the first and second amplification stages for splitting the amplified signal light into a C-band and a L-band; a reflector for reflecting the amplified output of the second amplifier stage back into the second amplifier stage and the first amplifier stage in a reverse direction; a combiner for combining the reflected output, in succession, from the second amplifier and first amplifier to produce an output signal; and, a circulator for redirecting the reflected output traveling in a reverse direction to the input of the combiner.

Abstract: An optical amplifier includes an optical amplification medium, an excitation source to stimulate the amplification medium to output at least one wavelength gain peak, and a gain equalizer to equalize the output of the amplification medium such that gain is produced at wavelengths other than the wavelength gain peak. The gain equalizer may attenuate gain at the peak wavelength. The gain equalizer may equalize the output of the amplification medium such that gain is produced at wavelengths less than the wavelength gain peak. The optical amplifier may include both a gain equalizer and automatic level control circuitry to respectively maintain substantially uniform gain at wavelengths within an optical signal band and maintain constant output power.

Abstract: An in-line broadband amplifier includes at least one input fiber and a WDM splitter coupled to the input fiber. The splitter splits an optical signal into at least a first wavelength and a second wavelength. A transition from a stop band to a pass band of the splitter occurs in 20 nm or less. A Raman amplifier and a rare-earth doped optical amplifier are coupled to the splitter. A WDM combiner is coupled to the Raman amplifier and the rare-earth doped optical amplifier. The WDM combiner combines an optical signal into at least a first wavelength and a second wavelength. A transition from a stop band to a pass band of the combiner occurs in 20 nm or less. An output fiber is coupled to the WDM combiner.

Abstract: Wideband optical amplifiers that use two parallel amplifiers in different operating spectral ranges and two different or identical sampled Bragg gratings as the channel splitter and combiner.

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 high power optical combiner (18) is provided for amplifying an optical signal. The combiner (18) includes a splitter (20) having a splitter input (22)and two splitter outputs (24, 26). The splitter input (22) receives an optical signal which the splitter divides (20) into two sub-signals. The splitter outputs (24, 26) have respectively coupled thereto a reference arm (30) and a dither arm (32). Both arms (30, 32) receive the sub-signals from the respective splitter outputs (24, 26) and transmit the sub-signals in parallel. Each arm (30, 32) has an amplifier (34) integrated therein for amplifying the sub-signals in parallel thereby producing amplified sub-signals. The high power optical combiner (18) further includes a combining coupler (42) connected to both arms (30, 32). The combining coupler (42) has two coupler inputs (46, 48), and a coupler output (50). The coupler inputs (46, 48) receive the amplified sub-signals from the arms (30, 32).

Abstract: A high-capacity optical transmission arrangement utilizing a plurality of laser sources and a plurality of wide-band optical amplifiers permit the reliable transmission of 1 Tb/sec rates over significant distances of optical fiber.

Abstract: A broadband optical amplifier is disclosed. The amplifier includes an input having a plurality of optical wavelengths, including optical wavelengths between 1610 and 1620 nanometers, and a first optical splitter optically connected to the input. The first optical splitter splits the input into a first band signal portion, a second band signal portion, and a third band signal portion. An amplifying portion is optically disposed along each of the first, second, and third band signal portions optically downstream from the first optical splitter. A first optical combiner is optically connected to the first, second, and third band signal portions to form an output. A method of amplifying a broadband optical signal is also disclosed.

Abstract: A system provides an input pump pulse and a signal pulse. A first dichroic beamsplitter is highly reflective for the input signal pulse and highly transmissive for the input pump pulse. A first optical parametric amplifier nonlinear crystal transfers part of the energy from the input pump pulse to the input signal pulse resulting in a first amplified signal pulse and a first depleted pump pulse. A second dichroic beamsplitter is highly reflective for the first amplified signal pulse and highly transmissive for the first depleted pump pulse. A second optical parametric amplifier nonlinear crystal transfers part of the energy from the first depleted pump pulse to the first amplified signal pulse resulting in a second amplified signal pulse and a second depleted pump pulse. A third dichroic beamsplitter receives the second amplified signal pulse and the second depleted pump pulse. The second depleted pump pulse is discarded.

Abstract: An optical amplifier, or optical repeater, for amplifying wavelength division multiplexed (WDM) light. A first demultiplexer demultiplexes the WDM light into first and second lights corresponding to different wavelengths in the WDM light. First and second optical amplifiers amplify the first and second lights, respectively. A first multiplexer multiplexes the amplified first and second lights into a multiplexed light. A dispersion compensator compensates for dispersion in the multiplexed light. A second demultiplexer demultiplexes the disperson compensated, multiplexed light into the first and second lights. Third and fourth optical amplifiers amplify the demultiplexed first and second lights, respectively. A second multiplexer multiplexes the amplified first and second lights from the third and fourth optical amplifiers into a WDM light. The optical amplifier can be configured so that the first and second lights travel through the dispersion compensator in opposite directions.

Abstract: An optical amplifier is disclosed. The amplifier includes an input and an optical splitter adapted to split the input into at least a first band signal portion and a second band signal portion. The first band signal portion includes a first reflector disposed optically downstream from the input, an amplifying gain medium disposed optically downstream from the first reflector, and a second reflector disposed optically downstream from the amplifying gain medium. A first amplifying power source is optically connected to the amplifying gain medium optically upstream from the amplifying gain medium and a second amplifying power source is optically connected to the amplifying gain medium optically downstream from the amplifying gain medium. The first reflector reflects a first light from the amplifying medium back into the amplifying medium and the second reflector reflects a second light from the amplifying medium back into the amplifying medium.

Abstract: In the optical amplifier an optical divider based on long wavelength (or short wavelength) transmission type dielectric multi-layer filter divides input signal light according to wavelengths, and amplifying sections disposed in parallel and having different respective wavelength amplification regions respectively amplify light signals emitted from the optical divider, and an optical combiner based on long wavelength (or short wavelength) transmission type dielectric multi-layer filter combines light signals output from the respective amplifying sections. In another configuration of the optical amplifier, input signal light is divided using an optical divider based on a dielectric multi-layer filter of a long wavelength (or short wavelength) transmission type, and output signals from the divider are filtered using an optical filter connected in series to a short wavelength (or long wavelength) amplifier generating a loss in the long wavelength (or short wavelength) region of the light signals.

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: In order to obtain optical transmission equipment for wavelength division multiplexing for providing a small inter-wavelength deviation regardless of a change in an input level, an amplification band is divided with wavelengths at inflection points in a wavelength gain characteristic of an impurity-doped fiber. The equipment includes an optical filter unit and a optical gain adjusting unit. The optical filter unit obtains filter characteristics associated with wavelength gain characteristics for a plurality of input levels by changing a temperature thereof. The optical gain adjusting unit includes a wavelength gain characteristic shift filter having a Peltier element for controlling the temperate of the optical filter unit.

Abstract: An optical amplifier includes a plurality of optical paths each carrying an optical signal and each including active optical fiber. A shared pump laser is coupled to the plurality of optical paths and provides pump power to the plurality of optical paths to individually amplify the optical signals. The plurality of optical paths includes input and output optical isolators and a coupler for coupling the pump power to the optical path. The active optical fiber is doped with an implant selected from the group of rare earth metals, erbium, ytterbium, and both ytterbium and erbium. A variable attenuator can be connected between the pump laser and the coupler of at least one of the plurality of optical paths or adjacent to the output isolator of one of the optical paths. Another optical amplifier serially couples optical signals to the optical path on a common gain media.

Abstract: An apparatus is provided including a source of spectrally dispersed seed wavelengths optically coupled to an array of fibers. Laser diode pumps are optically coupled to the array of fibers for amplifying the wavelengths through the array. A computer controlled feedback loop intercouples the array of fibers and laser diode pumps, the source of seed wavelengths and/or phase modulators for maintaining the wavelengths and relative phases in the array of fibers to desired levels. A compressor is optically coupled to an end of the array of fibers so as to receive and overlap the wavelengths from the individual fibers of the array.

Abstract: A Raman amplifier providing a wideband gain for use in a wavelength division multiplexing (WDM) optical communication system. In one embodiment, a first optical amplifier Raman amplifies a wavelength division multiplexed signal light in both a first wavelength band and a second wavelength band in accordance with a plurality of excitation (pumping) lights provided to the first optical amplifier, the first and second wavelength bands being different from each other. A divider divides the amplified signal light into first and second lights in the first and second wavelength bands, respectively. A second optical amplifier amplifies the first light and has a gain band in the first wavelength band. The third optical amplifier amplifies the second light and has a gain in the second wavelength band. In various embodiments, a gain equalizer and/or an optical isolator is used in combination with the first optical amplifier providing the Raman amplification.

Abstract: A fiber optic system implementing an amplification system is disclosed that provides distributed optical amplification through remote pump technology. The fiber optic system is comprised of a transmitting system, an amplification system, and a receiving system. The amplification system is comprised of a signal processing system and a laser system. The transmitting system transmits an optical signal that includes a C-band and L-band to the signal processing system. Concurrently, the laser system receives a single laser signal and transfers the single laser signal to the signal processing system. The signal processing system receives the single laser signal and the optical signal that includes the C-band and L-band, and combines the optical signal and the single laser signal to amplify the C-band and L-band of the optical signal.

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 &lgr;1 to &lgr;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 low noise optical amplifier used in an optical communication system includes optical amplifying elements for amplifying optical signals of a specific wavelength(&lgr;) incident from their ends(F1,F2) and endowing phase difference between ASEs, optical diverging means to interfere the amplified optical signals and the ASEs output from both ends(F1,F2), first path of length(L1) to optically connect the one end(F1) to first gate(D1) of the optical diverging means, and second path of length(L2) to optically connect the other end(F2) to second gate(D2) of the optical diverging means. The first and second paths are designed with distance(L1-L2) so that the amplified optical signal causes reinforcing interference at the third gate(D3) and destructive interference at the fourth gate(D4), and the ASE causes destructive interference at the third gate(D3) and reinforcing interference at fourth gate(D4).

Abstract: The invention proposes an optical amplifier for the C and L bands having a first stage with an amplification fiber (8) common to the C and L bands, a second stage with a branch (14) for C-band signals and a branch (12) for L-band signals with an amplification fiber (20). According to the invention, most of the power in the C band is created in the common amplification stage. The amplifier has a coupler (24) in the branch for C-band signals coupling pumping light for the amplification fiber of the first stage in the contrapropagating direction. The invention simplifies the structure of the amplifier and limits the number of devices through which L-band signals pass after they are amplified in the common amplification fiber of the first stage. It improves the L-band signal/noise ratio.

Abstract: A method and apparatus are provided for amplifying a first optical signal having a first wavelength and a second optical signal having a second wavelength. The method includes the steps of routing the first and second optical signal into a first and second optical amplifier coupled in parallel and amplifying the first optical signal at the first wavelength in the first optical amplifier and the second optical signal at the second wavelength in the second optical amplifier.

Abstract: Provided are optical amplifiers and method for amplifying an optical signal with an improved noise figure. This is achieved by exploiting the coherence (data) and incoherence of an optical. More specifically, an optical signal is split into two path signals that propagate and are amplified along two independent paths. The path signals each carry a signal path component and an external noise path component. After amplification the path signal each further carry an ASE (amplified spontaneous emission) path component wherein the ASE path components are un-correlated.

Abstract: An optical amplifier suitable for use in optical communication systems such as for telecommunications or cable television provides, for purposes of wavelength division multiplexed communications, the ability to amplify optical signals in both the C band, L band, and S band using conventional EDFA amplifiers. The S band, normally not amplifiable by EDFAs, here is amplified by converting the S band signal to a C band optical signal, providing optical amplification by an EDFA, then reconverting the amplified C band optical signal back to the S band in the same or a subsequent amplifier stage. The wavelength converters are, for instance, periodically poled lithium niobate devices using three-wave mixing, and employing difference frequency generation techniques.

Abstract: An optical amplifier for a 4-fiber system having two inputs and outputs is provided that makes use of a single amplifier rather than two separate amplifiers. The optical amplifier node makes use of an interleaver before and after the single amplifier to demultiplex and multiplex even and odd channel signals traveling in opposite directions. The arrangement can also amplify wide channel spaced signals traveling through a plurality of optical fibers. The optical amplifier node can be combined with other like amplifier nodes to provide more complex amplifier solutions at reduced costs due to the need for only half of the typical number of amplifiers. The optical amplifier node can also be combined with, e.g., variable optical attenuators, L/C/S filters, channel add/drop, co- and counter-propagating Raman amplification, and dispersion compensation modules to modify the optical signals as desired.

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.