Abstract: Polarization monitoring and control in a lightwave communication system is achieved by using an in-line polarimeter in conjunction with a polarization controller. The devices are readily compact, accurate and therefore capable of implementation in a variety of system applications. In one embodiment, a polarimeter and controller can be coupled together by a feedback loop between the polarimeter output and the controller input to provide “active polarization control” (APC).

Abstract: An optical signal is introduced into a polarization rotator to control the optical signal so that the output of the optical signal is maximized through the rotation of a plane of polarization of the optical signal, and then, introduced into the polarizer to pass a linear polarization of the optical signal therethrough, and then, introduced into the optical electric power detector to detect the output of the optical signal.

Abstract: A method and apparatus for polarization measurements. A polarization state of an optical signal can be determined using a polarization analyzer comprising a polarization controller, a polarizer, a wavelength dispersive element and a photo-detector. The method and apparatus can be applied to polarization and polarization mode dispersion measurements in wavelength division multiplexed communication systems.

Abstract: Method and apparatus for determining scattering parameters of a scattering matrix of an optical device. A method according to the present invention comprises applying an optical stimulus to a plurality of ports of the optical device, measuring optical fields emerging from the plurality of ports in amplitude and phase, and calculating the scattering parameters using the measured optical fields. The applying step includes applying the optical stimulus to the plurality of ports simultaneously. The method ensures a consistent phase reference for measurement of all of the scattering parameters so that all measurable characteristics of the device can be calculated directly from the scattering parameters.

Abstract: Methods and apparatus for coherent PMD generation are provided. A PMD generator can include at least four birefringent stages in optical series, thereby forming at least three pairs of adjacent stages. Each of the stages includes a harmonic differential group delay element and a phase-compensating element. The generator can be made colorless (i.e., made to have the same PMD at each WDM channel) and can be operated such that DGD and second order PMD can be independently generated and controlled. These PMD generators can be used in PMD compensators and PMD emulators.

Abstract: An optical device includes a small and low-cost variable polarization plane rotator that can control a rotation angle of the polarization plane easily. A variable polarization plane rotator is provided with a ?/4 phase plate having an optical axis in the same direction as, or at a 90 degree angle relative to, a polarization direction of an input light beam. A phase difference variable element has an optical axis at a ±45 degree angle relative to the optical axis of the ?/4 phase plate, to apply a variable phase difference between the polarization components parallel to and perpendicular to the optical axis thereof. A phase difference adjustment section adjusts the variable phase difference of the phase difference variable element, wherein the input light beam after being transmitted through the phase difference variable element to form elliptically polarized light or circularly polarized light, is transmitted through the ?/4 phase plate to form linearly polarized light.

Abstract: A method and apparatus for providing optical 3R regeneration involving: 1) generating an encoded optical clock signal from at least an optical signal; 2) introducing the encoded clock signal into a delay interference section of a regenerator such that an amplitude modulated clock signal is produced; andoutputting the amplitude modulated clock signal wherein the output amplitude modulated clock signal preserves information present within the input optical signal.

Abstract: According to the cross phase modulation suppressing device of the present invention, the wavelength multiplexing optical signal from an optical fiber having polarization orthogonality between the adjacent channels is split for every channel and the split optical signals are led to delaying optical waveguides of different lengths by the AWG (Arrayed Waveguide Grating) connected to a second port of an optical circulator, and the split optical signals with each delay added are reflected by the Farraday mirrors in polarization states orthogonal to each other and again led to the delaying optical waveguides. The reflected lights are combined by the AWG and supplied to a third port of the optical circulator as the wavelength multiplexing optical signal with orthogonality of polarization states kept between the adjacent channels.

Abstract: A method and apparatus for determining polarization-resolved scattering parameters of an optical device. A method comprises stimulating a port of the optical device with a stimulation field having at least two polarization states, measuring the optical field emerging from the port in amplitude and phase, and calculating the scattering parameters using the measurements. By stimulating a port of an optical device with a stimulation field having at least two different polarization states, measurements needed to determine scattering parameters of the optical device can be conducted by stimulating the port with only one sweep of a swept optical source.

Abstract: A PMD mitigation system is disclosed that is comprised of an interface coupled to a control system. The interface receives an optical signal and transfers the optical signal to the control system. The control system receives the optical signal from the interface, recovers a clock signal from the optical signal, optically reshapes the optical signal using the clock signal to generate a PMD mitigated signal, and transfers the PMD mitigated signal to the interface. The interface transmits the PMD mitigated signal. The PMD mitigation system advantageously mitigates PMD in the optical signal by optically reshaping the optical signal.

Abstract: A polarization mode dispersion generator for generating polarization mode dispersion (“PMD”) spectra is provided. The generator includes a plurality of birefringent stages, each stage including a differential group delay (“DGD”) element and a phase-shifting element. The generator is capable of inducing an amount of polarization mode-mixing between at least one adjacent pair of stages. The shape of a PMD spectrum can be preserved while frequency shifting the spectrum in either direction. Alternatively, the shape of the PMD spectrum can be changed without frequency shifting.

Abstract: The present invention is directed to an integrated system for performing dispersion compensation on wavelength channels in WDM or DWDM transmissions. The system includes a tunable integrated dispersion compensation module that performs chromatic dispersion compensation and polarization mode dispersion compensation on each of the wavelength channels in the transmission. Feedback is used to adjust the tunable integrated dispersion compensation module until receiver performance is optimized.

Abstract: The invention provides a polarization controller to set the state of polarization (SOP) of light in an optical fiber. A plurality of piezoelectric squeezers couple with an electronic drive to apply compression forces to the fiber. The drive applies voltage signals to the squeezers and monitors one or more of (a) a voltage across the squeezer, (b) a capacitance change with the fiber, (c) a force applied to the squeezer, (d) a force applied to the fiber, and (e) a resonance of one or more squeezers. Feedback from one or more of (a)-(e) is used to modify the applied voltage signals in control of the SOP.

Abstract: A spread polarization transmitter for transmitting at least one light signal comprises a spread-spectrum communication apparatus and a polarization modulator. The spread-spectrum communication apparatus modulates the at least one light signal according to a spread-spectrum modulation technique. The polarization modulator comprises a polarizer and a magnetic bubble waveguide. The polarizer is capable of polarizing the at least one spread-spectrum modulated light signal in a polarized direction. And the magnetic bubble waveguide, which is configured in accordance with a pseudo-random polarization code sequence such that the plurality of magnetic bubble domains assume a time varying position representative of the pseudo-random polarization code sequence, is capable of receiving at least one polarized, spread-spectrum modulated light signal.

Abstract: Methods and apparatus for coherent PMD generation are provided. A PMD generator can include at least four birefringent stages in optical series, thereby forming at least three pairs of adjacent stages. Each of the stages includes a harmonic differential group delay element and a phase-compensating element. The generator can be made colorless (i.e., made to have the same PMD at each WDM channel) and can be operated such that DGD and second order PMD can be independently generated and controlled. These PMD generators can be used in PMD compensators and PMD emulators.

Abstract: The present invention provides a method and apparatus for compensating for polarization mode dispersion in an optical transmission system without perturbing the laser source. The present invention compensates for PMD by transferring a sufficient fraction of the light signal in an optical transmission system substantially into a single PSP of the system. As a result, each light pulse in a data stream is not substantially mixed with temporally adjacent light pulses or bit periods.

Abstract: A polarization scrambler unit includes a plurality of polarization scramblers, a switching unit for coupling one of the polarization scramblers to a transmission line fiber, a detection unit for detecting an output signal from the polarization scrambler coupled to the transmission line fiber, and a controlling unit for switching, via the switching unit, between the polarization scramblers and another polarization scrambler whenever a false output signal is detected by the detection unit. Thus, the polarization scrambler unit has a redundant structure.

Abstract: Methods and apparatus for coherent polarization mode dispersion generation are provided. A generator can include at least four birefringent stages. The birefringent stages are in optical series, and each includes a differential group delay (“DGD”) element. The intermediate stages' DGD elements are harmonic. Also, these intermediate stages each include a phase-shifting element. The generator can also include a polarization mode-mixing apparatus and a variable phase-shifting apparatus. The mode-mixing apparatus is capable of inducing polarization mode-mixing between at least one pair of adjacent stages to generate DGD and second order PMD independently at at least one optical frequency. The variable phase-shifting apparatus can include a phase-shifting controller coupled to each of said phase-shifting elements. A graphical user interface for PMD emulation, a PMD compensator for reducing PMD impairment, and calibration methods are also provided.

Abstract: An object of the invention is to provide a method and apparatus of PMD compensation, which enable of compensating for polarization-mode dispersion (PMD) occurring in signal light, at high accuracy over a wide range.

Abstract: An optical circulator has optical elements structured to control return loss for light propagating from an input port to an output port. In some embodiments, the optical circulator has a port configuration that aligns a first optical port along the central axis of a first lens, aligns a second optical port along the central axis of a second lens and positions a third optical port adjacent to the first optical port. A light adjusting optical element may be included to adjust the direction of light emanating from the first optical port and the direction of light propagating to the third optical port to be parallel to each other.

Abstract: An optical device includes a small and low-cost variable polarization plane rotator that can control a rotation angle of the polarization plane easily. A variable polarization plane rotator is provided with a &lgr;/4 phase plate having an optical axis in the same direction as, or at a 90 degree angle relative to, a polarization direction of an input light beam. A phase difference variable element has an optical axis at a ±45 degree angle relative to the optical axis of the &lgr;/4 phase plate, to apply a variable phase difference between the polarization components parallel to and perpendicular to the optical axis thereof. A phase difference adjustment section adjusts the variable phase difference of the phase difference variable element, wherein the input light beam after being transmitted through the phase difference variable element to form elliptically polarized light or circularly polarized light, is transmitted through the &lgr;/4 phase plate to form linearly polarized light.

Abstract: In the invention, an input light including a signal light and a noise light within a signal wavelength band of the signal light is divided into a first component with a polarization parallel to a polarization direction of the signal light and a second component with a polarization orthogonal to the polarization direction of the first component. The first component is supplied into a first arm and the second component into a second arm. The optical phase of the second component in the second arm is shifted so that the optical phase of the second component in the second arm relatively differs by &pgr; from the optical phase of the first component in the first arm. The first component output from the first arm and the second component output from the second arm are combined to make the noise lights included in the first and second components interfere with each other.

Abstract: A signal light from an optical transmission line propagates on a first optical fiber and enters a polarization converter. The polarization converter converts the input light with the given polarization into a linear polarization with a desired angle using two Faraday rotators and a quarter wave plate between them. The output light of the polarization converter propagates on a second optical fiber and enters a polarization beam splitter. The polarization beam splitter splits the light from the second optical fiber into two mutually orthogonal polarization components (e.g. TE and TM components) and outputs either of them (e.g. the TE component) toward a third optical fiber. A portion of the light propagating on the third optical fiber is split by an optical coupler and enters a photodetector. A bandpass filter (BPF) extracts a clock component of the signal from an output of the photodetector.

Abstract: A micro-optical delay element for a time-division multiplexing scheme is disclosed wherein two light beams are provided to a beam splitter/combiner (BS/C) in the absence of optical fibre. At least one beam exiting a modulator is collimated and reaches the (BS/C) unguided as a substantially collimated beam.

Abstract: A polarization diversity receiver has an optical section for converting the received optical signal into four or five polarization diverse component optical signals that substantially represent amplitude and polarization state information of the received optical signal, by respective polarization transformations to respective points on a Poincaré sphere, the points being equally spaced apart to maximise polarization diversity, even in the worst case input polarization state. Detectors produce component electrical signals from each of the component optical signals, for electronic processing to compensate for PMD. By reducing the number of component optical signals significant cost and size reductions are enabled. The need for precise polarization tracking in the receiver can be reduced or eliminated completely. Balanced detectors can be used to reduce the number of electrical signals. The electrical processing can use sequence detection.

Abstract: Systems, apparatuses, and methods for producing and utilizing orthogonal optical data signals, which can be produced by modulating electrical data signals onto orthogonal polarization components of an optical carrier traveling in opposite directions in a common modulator. The modulator can include one or more traveling wave electrodes having first and second ends with a first electrical data input connected to the first end and a second electrical data input connected to the second end.

Abstract: An optical clock multiplier comprises a phase modulator (12) to shift a phase in pulse duration of an input optical clock pulse by &pgr;, a polarization mode dispersion device (16) having a predetermined time difference between first and second polarizations orthogonal to each other to divide an output light from the phase modulator into the first and second polarization components, and a polarization device (20) to extract one of polarization components in a third polarization practically inclined at an angle of 45° against the first polarization and a fourth polarization orthogonal to the third polarization out of the output light from the polarization mode dispersion device.

Abstract: The invention is related to a Raman pump source with a first laser diode (40) and a second laser diode (41), a coupler (43) and a polarization beam combiner (46). The signals of the two laser diodes are combined in a polarization maintaining coupler (43) with two in- and two outputs, and the outputs of the coupler (43) are linked to the polarization beam combiner.

Abstract: A dispersion compensation controlling apparatus used in a very high-speed optical communication system adopting optical time division multiplexing system comprises a first specific frequency component detecting unit (2a) detecting a first specific frequency-component in a baseband spectrum in a transmission optical signal inputted to a receiving side over a transmission fiber as a transmission line (6a), a first intensity detecting unit (3a) detecting information on an intensity of the first specific frequency component detected by the first specific frequency component detecting unit (2a and a polarization-mode dispersion controlling unit (220a) con trolling a polarization-mode dispersion quantity of the transmission line (6a) such that the intensity of the first specific frequency component detected by the first intensity detecting unit. (3a) becomes the maximum, thereby easily detecting and compensating polarization-mode dispersion generated in a high-speed optical signal.

Abstract: A polarization mode dispersion (PMD) compensation arrangement receives an optical input data signal which has been subjected to PMD. The arrangement comprises an adaptive chromatic dispersion compensator (24) and a first-order PMD compensator (20,22) in series, wherein the adaptive chromatic dispersion compensator is controlled to provide compensation for both chromatic dispersion and second order PMD. The compensation arrangement is used in a node of an optical network.

Abstract: Methods and systems for PMD compensation in an optical communication system are implemented by transmitting multiple optical signals through a common optical conduit to an optical compensator that adjustably rotates the polarization states of the multiple optical signals and transmits the rotated optical signals to an optical receiver. The receiver, upon sensing an excessive error condition, commands the optical compensator to change the polarization state of rotation, which changes the PMD profile of the received optical signals.

Abstract: With this polarization mode dispersion compensation method, an optical signal which is sent by an optical signal transmitter 5 is propagated along an optical transmission path 6, and, after having passed through a polarization controller 1, is inputted to a polarizer 2. A specified polarization component is separated out by the polarizer 2 from this optical signal which has been thus inputted. The optical signal which has been thus separated is inputted into a waveform deterioration detector 3, which detects waveform deterioration thereof. Based upon information related to the waveform deterioration which has been detected, a control device 7 controls the polarization controller 1 so that the waveform deterioration becomes a minimum.

Abstract: A method and system of coherent detection of optical signals. The system utilizes a digital signal processor to recover an incoming optical signal. The system employs a local oscillator, which does not need to be phase locked to the signal. The signal may be consistently recovered, even when the polarization state varies over time. Additionally, the signal may be recovered when it comprises two channels of the same wavelength that are polarization multiplexed together. In addition, any impairment to the signal may be reversed or eliminated.

Abstract: Transmission characteristics of a multiplicity of light signals each having a different frequency are compensated for simply and at a high accuracy by use of a single type of or a few types of variable optical equalizers, thereby enabling an optical multiplex transmission system having excellent transmission band characteristics to be implemented. Variable Faraday rotators 51, 52 and a polarization dependent element 6 are disposed on an optic axis (Z-axis) extending between an input-side fiber collimator 21 for emitting in the form of a beam signal light transmitted over an optical fiber 1 and an output-side fiber collimator 22 for causing the optical fiber 1 to transmit the signal light input in the form of a beam.

Abstract: A method for compensating for chromatic dispersion of an optical signal includes: receiving the optical signal from an input fiber; collimating the optical signal using a collimator; delivering the collimated optical signal to a Gires-Tournois interferometer; reflecting a chromatic-dispersion-compensated optical signal from the Gires-Tournois interferometer to the collimator; focusing the chromatic-dispersion compensated optical signal into an output fiber. The compensator in accordance with the present invention provides flexibility in producing periodically varying chromatic dispersion so as to compensate for unwanted periodic chromatic dispersion produced in an interferometric interleaved channel separator. Also, the compensator enables compensation of fiber optic chromatic dispersion.

Abstract: A method and apparatus is provided that yields improved performance of both single channel and WDM long-distance optical transmission systems by synchronously modulating of the transmitted signal's amplitude. An amplitude modulator receives an optical signal onto which data has been modulated at a predetermined frequency. The modulator re-modulates the amplitude of the optical signal in a continues fashion with a waveform that is periodic, whose fundamental frequency is equal to the same predetermined frequency at which the data is modulated onto the optical signal. The resulting signal (which is neither a pure NRZ or RZ signal) is more tolerant to the distortions usually found in lightwave transmission systems, thus giving superior transmission performance.

Abstract: The present invention provides a chromatic dispersion and polarization mode dispersion compensator utilizing a Virtually Imaged Phased Array (VIPA) and birefringent wedges to moderate chromatic dispersion and polarization mode dispersion (PMD). The compensator in accordance with the present invention propagates the composite optical signal in a forward direction; separates the wavelengths in the band of wavelengths in each of the plurality of channels, where the each of the wavelengths in the band is spatially distinguishable from the other wavelengths in the band; spatially separates each wavelength of each band of wavelengths into a plurality of polarized rays; and reflects the plurality of polarized rays toward a return direction, where dispersion is added to the reflected plurality of polarized rays such that the unwanted chromatic dispersion and PMD are compensated.

Abstract: A polarized input optical beam enters a polarization beam splitter/combiner (PBC), where a first polarization component of the polarized input optical beam continues to propagate substantially entirely along a first optical path, whereas at least a portion of a second orthogonally polarized component switches onto a second optical path. A loop back optical fiber incorporated in at least one of the first and second optical paths, adds propagation delay length greater than the coherence length of the polarized input optical beam, giving rise to delayed and undelayed optical beam components, which are then incoherently recombined into a depolarized output optical beam.

Abstract: A communication device uses one or two stacks of reflective deflectors to steer the electromagnetic waves carrying signals received and transmitted through a single telescope/aperture device. The signals outside the device may be circularly polarized while inside the device they are linearly polarized most of the time. The deflectors within each stack are transparent to the signals steered by the deflectors behind them. Since the deflecting wave band may shift with the changing angle of incidence of the signals due to steering, the wave bands are sufficiently spaced apart. When the signals impact the deflectors at nearly normal angles, the wave bands can be made more narrow. When more than one stack of deflectors is used, the spacing between the wave bands within one stack may be utilized by another stack.

Abstract: According to an exemplary embodiment of the present invention, an optical waveguide and method of use includes a grating which has a grating parameter that is adapted for dynamically variable non-uniform alteration. The non-uniform alteration of the grating parameter results in the introduction of a predetermined amount of chromatic dispersion and dispersion slope into an optical signal traversing the waveguide. According to another exemplary embodiment of the present invention, an optical apparatus and method of use includes a plurality of optical waveguides each of which have an optical grating and at least one of the waveguide gratings has a grating parameter that is adapted for dynamically variable non-uniform alteration. The optical apparatus further includes a device, which dynamically varies the grating parameters of each of the waveguides to selectively introduce chromatic dispersion and dispersion slope into an optical signal traversing the apparatus.

Abstract: The present invention provides an improved optical wavelength switch in which no mechanical movement is required to direct optical pathways between several fiber ports. The inventive three-fiber port device divides incoming optical signals into two subsets of spectra and selectively directs them into two output ports in response to an electrical control signal. In the inventive switch, an optical signal is spatially split into two polarized beams, by a birefringent element, which thereafter pass through a series polarization rotation elements and recombine into output fibers, achieving polarization independent operation. Advantageously, the inventive switch incorporates two-stage polarization rotations to improve isolation depth, as well as temperature and wavelength independence. The invention also incorporates light bending devices to allow two fibers to be coupled to the light beams via a single lens, thereby achieving small beam separation for compactness.

Abstract: Methods and systems for implementing polarization division multiplexing to allow recovery of data in different multiplexed channels at a receiving end without recovering multiplexed polarizations used in the transmitting stage.

Abstract: To increase the bit rate at which and the distance over which data can be transmitted by optical fiber, polarization dispersion is compensated by means of a polarization controller, a system for generating a differential group delay between two orthogonal modes of polarization and a control unit of the polarization controller. A chromatic dispersion compensator applies compensation which is adjusted dynamically to optimize the quality of the received optical signal. Applications include long-haul optical transmission on standard fibers.

Abstract: A fiber optic communications link having PMD characterization across multiple optical channels to identify PMD problems. The communications link has adaptive PMD controls employed along the optical link, whereby PMD phenomena detected by instruments, such as PMD compensators, are interpreted as being either attributable to perturbation of fiber characteristics at large, or by failure of PMD equipment along the link. The present invention avoids taking unnecessary control or maintenance actions upon PMD related controllers and compensators. PMD notifications from various PMD compensators are correlated to identify which portion of the link has undergone a change in polarization characteristics to further identify PMD related errors and problems.

Abstract: The present invention is a device to increase the bit rate and distance at which data can be transmitted by optical fiber. The device compensates the polarization dispersion of the line by processing a received optical signal with the use of a polarization controller, the generation of a differential group delay between two orthogonal polarization modes and a control unit for the polarization controller. The data that is sent is redundant to enable detection of errors affecting the data received and the control unit is adapted to minimize the error rate calculated in real time by using the redundant data. The application of the device is to long-haul optical transmission, in particular over stranded fibers.

Abstract: An all-optical 3R regenerator (AO3R) and a method for using the AO3R to retime, reshape and retransmit an optical signal are described herein. The AO3R includes a polarizer that receives an input optical signal which is of unknown, potentially varying phase and outputs a stable polarized input optical signal. The AO3R also includes a first interferometer (e.g., interferometric converter module) that retimes and reshapes the polarized input optical signal and transmits the retimed and reshaped polarized input optical signal as a polarized output optical signal. The first interferometer is able to retime the polarized input optical signal with the aid of a laser and a clock recovery mechanism.

Abstract: A method and apparatus for managing state-of-polarization (SOP) controllers along an optical communications link. When the polarization-mode dispersion (PMD) in the link exceeds a preset limit as determined by a PMD compensator, the SOP controller is directed to change rotation angle in an arbitrary fashion. This shift is only undertaken after other indicators are examined to determine that PMD is the main problem affecting the link, and not simply a consequence of a separate problem that the SOP controller rotation angle should not try to fix. By reducing unnecessary SOP adjustments which can disrupt data traffic, the reliability of the optical link is improved.

Abstract: A polarization-independent optical switch is disclosed for switching at least one incoming beam from at least one input source to at least one output drain.

Abstract: Use of a filter in lieu of a secondary reflector in a reflective telescope provides compact design that eliminates the obstruction caused by the secondary reflector. The filter is selectively reflective to either the angle of incidence of radiation striking the filter or to the polarization exhibited by the radiation. An angularly sensitive filter may be constructed to either a bandpass filter or a short pass filter. A filter that is sensitive to polarization is constructed from a cholesteric liquid crystal. The filter is disposed in front of a primary reflector that comprises an aperture for collecting radiation observed by the telescope.

Abstract: The present invention offers a polarization mode dispersion compensator and a compensation method for polarization mode dispersion having simple constitution and being strong against external disturbances. The polarization mode dispersion compensator, a representative example of the present invention, is provided with a compensation circuit for polarization mode dispersion, a degree of polarization measuring circuit, and a control circuit. An optical signal is input to the compensation circuit for polarization mode dispersion through an optical fiber, and after the process of compensation for polarization mode dispersion, it is output to an optical fiber. An optical coupler divides a part of the optical signal passing through the optical fiber. The degree of polarization measuring circuit finds the degree of polarization of the divided optical signal.