Abstract: The present invention provides systems and methods for the mitigation of PMD impairments in fiber optic links. The present invention utilizes synchronous polarization modulation and digital control of polarization modulation, instead of independent polarization modulators and analog control used in the current state of art. Also, the present invention utilizes a feedback loop to avoid identified bad polarization states instead of a random open loop operation. Further, the present invention includes a mechanism to continually update polarization states based on pre-corrected FEC error analysis from data receivers. Additionally, the present invention includes a mechanism for collecting and correlating error feedback signals from multiple geographically-diverse network nodes. Advantageously, the present invention provides a cost-effective and efficient way to implement mitigation of PMD impairments, while using only a small fraction of the FEC error correction capability.

Abstract: The present disclosure provides polarization mode dispersion compensation (PMDC) and polarization de-multiplexing systems and methods for polarization multiplexed (PolMux) optical transmission systems. The PMDC detects an error signal before a polarization splitter in PolMux systems for controlling polarization controllers (PC) and/or DGDs in the PMDC for return-to-zero (RZ) differential m-phase shift keying (DmPSK) signals. For bit-aligned PolMux systems, the error signal could be the level of clock frequency at one, two, or more times of the baud rate at one polarization. For bit-interleaved PolMux systems, the error signal could be the level of clock frequency at two times of the baud rate at one polarization. The PMDC can operate in PolMux systems with any arbitrary time offset between the two polarizations. The polarization de-multiplexer utilizes error detection at both output arms of a polarization splitter to mitigate PDL impact on any PolMux type of signal.

Abstract: An optical transmitter apparatus for use in an optical communications network has a polarization dithering unit, an optical transmitter unit, and a transmission fiber. The polarization dithering unit is connected in series between an output of the optical transmitter unit and the transmission fiber.

Abstract: A signal equalizer for compensating impairments of an optical signal received through a link of a high speed optical communications network. At least one set of compensation vectors are computed for compensating at least two distinct types of impairments. A frequency domain processor is coupled to receive respective raw multi-bit in-phase (I) and quadrature (Q) sample streams of each received polarization of the optical signal. The frequency domain processor operates to digitally process the multi-bit sample streams, using the compensation vectors, to generate multi-bit estimates of symbols modulated onto each transmitted polarization of the optical signal. The frequency domain processor exhibits respective different responses to each one of the at least two distinct types of impairments.

Abstract: Systems and techniques for optical communications based on polarization division multiplexing are described.

Abstract: A coherent optical receiver of the invention combines local oscillator light having orthogonal polarization components in which the optical frequencies are different to each other, and received signal light, in an optical hybrid circuit, and then photoelectrically converts this in two differential photodetectors. Then this is converted to a digital signal in an AD conversion circuit, and computation processing is executed in a digital computing circuit using the digital signal, to estimate received data. At this time, the optical frequency difference between the orthogonal polarization components of the local oscillator light is set so as to be smaller than two times the signal light band width, and larger than a spectrum line width of the signal light source and the local oscillator light source. As a result, it is possible to realize a small size polarization independent coherent optical receiver that is capable of receiving high speed signal light.

Abstract: A signal equalizer for compensating impairments of an optical signal received through a link of a high speed optical communications network. At least one set of compensation vectors are computed for compensating at least two distinct types of impairments. A frequency domain processor is coupled to receive respective raw multi-bit in-phase (I) and quadrature (Q) sample streams of each received polarization of the optical signal. The frequency domain processor operates to digitally process the multi-bit sample streams, using the compensation vectors, to generate multi-bit estimates of symbols modulated onto each transmitted polarization of the optical signal. The frequency domain processor exhibits respective different responses to each one of the at least two distinct types of impairments.

Abstract: A simplified optical receiver architecture capable of tracking and demultiplexing polarization-multiplexed signals, dynamically compensating for PMD using a variety of polarization controller technologies, and reducing the number of delay line demodulators by two for both DPSK and DQPSK modulation is illustrated. Once polarization is stabilized at the first stage of the cascaded system of the present invention, subsequent stages can be simplified and cost reduced.

Abstract: A turbo equalizer includes a Bahl-Cocke-Jelinek-Raviv (BCJR) equalizer configured to receive a transmitted signal and partially cancel inter-symbol interference (ISI) due to polarization-mode dispersion (PMD). A low-density parity check (LDPC) decoder is coupled to the BCJR equalizer to receive channel bit reliabilities therefrom. The LDPC decoder iteratively provides extrinsic soft information feedback to the BCJR equalizer to compensate for PMD.

Abstract: This application describes optical monitoring devices and applications in optical systems for monitoring various optical parameters of light, including the signal to noise ratio, the degree of polarization, and the differential group delay (DGD).

Abstract: An optical signal of an optical transmission part is brought into a high-speed polarization scrambling state by a polarization scrambling part, and transmitted to en optical fiber transmission line as the optical signal from the optical transmitter. The optical signal passing through the optical fiber transmission line is inputted to an optical receiver. The optical signal inputted to the optical receiver is converted into an electric signal by a polarization dependent photoelectric detection part. The converted electric signal is inputted to a digital signal processing part having a polarization scrambling cancel part of canceling the polarization scrambling state by a digital signal processing operation. At the digital signal processing part, the polarization scrambling state of the electric signal is canceled, and a data signal is outputted.

Abstract: The invention relates to a method of generating a feedback signal for adjusting a polarization mode dispersion compensator (PMDC, 21) in a transmission system with alternate-polarization. A first signal (37) is determined by measuring a spectral component of the radio frequency modulation of an optical signal (33) at a particular radio frequency. Preferably, the radio frequency essentially corresponds to half the symbol rate of the optical signal (33). Also a second signal (35) is determined by coupling the optical signal (33) into a delay line interferometer (DLI, 50) having a delay essentially corresponding to the symbol period or an odd multiple of the symbol period between its arms (51, 54). Downstream of the DLI (50), the signal is optical-to-electrically converted. Downstream of the optical-to-electrical conversion, an intensity measurement is performed. The first (37) and second (35) signals are then combined to generate the feedback signal (28).

Abstract: The invention relates to a method and a system for controlling a PMD compensator (2). For this purpose, a measuring signal (MS) is branched off from an already compensated optical data signal (ODSK) and supplied to a polarization adjuster (2). The output signal of the latter is supplied to an optical filter unit (61) and subdivided into two optical measuring signal components (OMK1, OMK2) having different polarizations. After a respective opto-electrical conversion, the spectra are compared with each other in an analysis and control unit (81) and the PMD compensator (2) is adjusted in such a manner that they are as identical as possible.

Abstract: Efficient apparatus, methods, systems and devices to generate, transmit and detect optical differential polarization-phase-shift keying signals are disclosed for high spectral efficiency optical communication systems. It includes an electrical encoder and an optical encoder for generation of differentially encoded polarization-phase modulated optical signals and optical demodulators and balanced detectors for detection of the optical signals. The optical signals are transmitted through optical fiber links or free space. The electrical encoder maps independent data channels into differentially-encoded data sequences. In the optical encoder, the encoded data sequences from the electrical encoder drive optical modulators to generate differentially-encoded polarization-phase modulated optical signals at a symbol rate equal to the bit rate of each input data channel.

Abstract: In a method and an optical switch by which a signal light is accurately switched even if a polarization state of a signal light inputted has a fluctuation, power of an output light of a polarizer which receives a signal light extracted from an output light of a nonlinear optical medium is monitored and a polarization state of an input signal light to the nonlinear optical medium is controlled so that the power becomes minimum (or maximum). The polarization state of the input signal light is monitored, a calculation of performing a predetermined conversion is executed to the polarization state of the input signal light, and a calculated polarization state is recorded (or recorded without conversion). A polarization state of a control light with respect to the input signal light is monitored and the polarization state of the control light is controlled so as to coincide with the polarization state of the input signal light recorded.

Abstract: A communication system capable of employing polarization-dependent phase modulators with a reversing configuration that preserves security against disturbance of a polarization state at a transmission path but without using Faraday mirrors and a communication method using the same are provided. A quantum cryptography system of the present invention includes a first station 1, a transmission path 2, and a second station 3. The first station 1 has means for emitting time-divided optical pulses into the transmission path 2 and measuring a phase difference between the optical pulses returning from the transmission path 2. The transmission path 2 is a medium of light.

Abstract: The invention related to the system and method for optical communication using light of two polarization states. Polarization distortion loss (PDL) is compensated by implementation of polarization controllers at both the transmitter and receiver sides. The transmitter controller performs a mixing transformation of beam with two polarizations, while the receiver controller performs the same transformation in the opposite direction with exactly same sequence as in the transmitter part. A cross scrambling and a polarization rotation represented by matrix multiplication are examples of such mixing polarization transformations. The averaged PDL induced errors are corrected by the FEC code plus interleavers.

Abstract: A system and method are provided for calibrating skew in a multichannel optical transport network (OTN) transmission device. The method accepts a pair of 2n-phase shift keying (2nPSK) modulated signals via Ix and Qx electrical signal paths, where n>1. Likewise, a pair of 2p-PSK modulated signals are accepted via Iy and Qy electrical signal paths where p>1. The Ix, Qx, Iy, and Qy signals are correlated to a preamble/header portion of an OTN frame. A voltage on the Ix signal path is compared with Qx, and VO12 voltage is generated. A voltage on the Iy signal path is compared with Qy, and VO34 is generated. One of the Ix or Qx voltages is compared with one of Iy or Qy voltages to generate VOxy. Then, the VO voltages are minimized in response to adjusting time delay modules in the Ix, Qx, Iy, and Qy signals paths.

Abstract: This invention relates to crosstalk coefficient estimating apparatus and crosstalk coefficient estimating method. The crosstalk coefficient estimating apparatus is used to estimate a crosstalk coefficient of crosstalk inflicted on one channel of an optical fiber transmission system comprising two or more channels. The crosstalk coefficient estimating apparatus comprises a complex conjugate unit, for obtaining a complex conjugate signal for signal in one polarization-state of another channel other than said one channel; a multiplying unit, for multiplying the complex conjugate signal obtained by the complex conjugate unit with signal in another polarization-state of the another channel; and a filter, for filtering the multiplication result of the multiplying unit to obtain a crosstalk coefficient of crosstalk inflicted on the signal in one polarization-state of said one channel, wherein a transmission function of the filter is set according to system parameters of the optical fiber transmission system.

Abstract: A signal-light detection apparatus includes a polarization extractor that extracts a polarization component that is substantially in parallel with a specified axial direction from an input light, a polarization rotator that changes a relative angle between a direction of polarization of the input light and an axial direction of the polarization extractor, a photodetector that detects an optical power of the polarization component extracted by the polarization extractor, and a determination device that determines whether the input light includes a signal component, based on a variation in the optical power detected by the photodetector.

Abstract: A system and method are provided for controlling time delay in a multichannel optical transport network transmission device. The method accepts a pair of 2n-phase shift keying (2nPSK) modulated signals via Ix and Qx electrical signal paths, where n>1, and a pair of 2p-PSK modulated signals via Iy and Qy electrical signal paths where p>1. A voltage V1 on the Ix signal path is compared with a voltage V2 on the Qx signal path, and a VOx voltage in generated, which is minimized by adjusting time delay modules in the Ix and Qx signals paths. Likewise, a voltage V3 (Iy) is compared with a voltage V4 (Qy), and a VOy voltage is generated and minimized. Subsequent to minimizing VOx and VOy, the sum of V1 and V2 (V12) is compared with the sum of V3 and V4 (V34), and a VOxy voltage is generated and minimized.

Abstract: A coherent optical receiver of the invention combines local oscillator light having orthogonal polarization components in which the optical frequencies are different to each other, and received signal light, in an optical hybrid circuit, and then photoelectrically converts this in two differential photodetectors. Then this is converted to a digital signal in an AD conversion circuit, and computation processing is executed in a digital computing circuit using the digital signal, to estimate received data. At this time, the optical frequency difference between the orthogonal polarization components of the local oscillator light is set so as to be smaller than two times the signal light band width, and larger than a spectrum line width of the signal light source and the local oscillator light source. As a result, it is possible to realize a small size polarization independent coherent optical receiver that is capable of receiving high speed signal light.

Abstract: Photonic signals are tagged with a pre-selected modification, such as a polarization signature to carry data across an obstructed path between sender and receiver. Communication authentication through polarization variation allows for Yuen-Kumar or entangled photon quantum communication protocols to propagate through environmental scattering media such as air, smoke, fog, rain, and water. While ultraviolet light photons are well suited as a carrier for quantum communication signals scattered in air, it is appreciated that visible wavelengths have longer propagation paths in water to convey non-line-of-sight data. A secure signal is scattered by the media and simultaneously communicated to a single recipient or multiple recipients exposed to scattered signal portions. A process of solving the scattering processes through a random scattering media is provided to reconstruct a quantum keyed message at a receiver.

Abstract: In a coherent optical receiver, a method of at least partially compensating Polarization Dependent Loss (PDL) of an optical signal received through an optical communications system. A respective multi-bit sample stream of each one of a pair of orthogonal received polarizations of the optical signal is tapped, and used to derive a respective metric value indicative of a quality of each multi-bit sample stream. A gain of an analog front end of the coherent optical receiver is adjusted based on the derived metric values.

Abstract: The present invention is directed to an in-passband signaling method. The method includes the steps of extracting a control component and a data component from an optical signal. The control component may be used to determine the state of an optical switch in either a packet-switched network or circuit-switched network. The state of the optical switch is switched based on the extracted control signal. The control component may also be used to provide other network functions such as network operations, administration, and management (OA&M), network monitoring, and network control and management (NC&M). The control component is erased by polarization realignment of the optical signal. The control component is updated by remodulating the polarization state of the data component.

Abstract: An embodiment of the invention includes a tunable optical dispersion compensator (TODC) comprising a first beam displacer on an optical path, wherein the first beam displacer separates an optical signal into a first beam and a second beam, and one or more polarizing beam splitters on the optical path, wherein the one or more polarizing beam splitters keep the first beam and the second beam on the optical path. The TODC also comprises one or more etalons on the optical path, wherein the one or more etalons are tunable to introduce a group delay in the first beam and the second beam, and a reflecting mirror on the optical path, wherein the reflecting mirror returns the optical signal back along the optical path. The TODC further comprises a second beam displacer, wherein the second beam displacer combines the first beam and the second beam into an output optical signal.

Abstract: A fiber optic communication system including a fiber optic link, a transmitter system and a receiver system. The transmitter system includes a laser source producing a light beam, and a polarization controller receiving the light beam and providing an expected pattern of changing states of polarization to the light beam to output light signals into the fiber optic link to cause the expected pattern of changing states of polarization to be transmitted along the fiber optic link. The receiver system is provided with a polarization analyzer, and a light detector. The light detector receives the light signals transmitted by the transmitter, and forwards data indicative of the light signals to the polarization analyzer. The polarization analyzer analyzing the data with an inverse polarization reference frame and generates an alert based on deviations of the data from the expected pattern of changing states of polarization.

Abstract: A method and system for averaging the effects of polarization distortions across a multitude of transmitted data streams in a dual polarization multiplexed optical communications system. Data streams are interleaved amongst each other in accordance with a predetermined pattern. The interleaved data streams are symbol mapped and modulated to provide a pair of optical signals. The pair of optical signals are orthogonally polarized, and multiplexed for transmission across an optical fiber. A receiver circuit receives the transmitted signal and extracts the interleaved data streams. The interleaved data streams are de-interleaved to generate the original data streams. While the data streams can be interleaved and transmitted via a single wavelength optical signal, the data streams can be interleaved and transmitted over two or more different wavelength optical signals to further mitigate the effects of polarization distortions.

Abstract: A method of analysing an input signal, the method including the steps of: (a) dividing a first input signal into first and second orthogonal signal polarisation components; (b) dividing a second input signal into orthogonal first and second orthogonal local polarisation components; (c) mixing the first orthogonal signal component with the second orthogonal local polarisation component to provide a first mixed signal; (d) mixing the second orthogonal signal component with the first orthogonal local polarisation component to provide a second mixed signal; (e) analysing the first and second mixed signal to determine the polarisation or phase information in the input signal.

Abstract: At least two light beams with polarization diversity are generated that each carry a representation of the same information. Separate optic fibers carry each of the at least two beams through a region subject to vibration to a remote location where the information is recovered by an optical receiver based on the separate light beams. Using separate fibers to carry polarization diverse information minimizes polarization noise at the optical receiver due to vibration of the fibers.

Abstract: A surface emitting laser includes a plurality of light-emitting portions for emitting laser light beams in different linearly polarized light directions. The light-emitting portions are formed on the substrate and located close to each other. The light-emitting portions include metal opening arrays through which light beams in different linearly polarized light directions respectively pass.

Abstract: The invention aims to provide a monitoring method that can measure an optical SNR in an ultra high speed optical transmission system with high accuracy, and an optical transmission system using the same. To this end, in the optical transmission system to which the monitoring method of the present invention is applied, the degree of polarization of an optical signal transmitted from an optical transmission apparatus to an optical receiving apparatus via an optical transmission path is measured by a DOP measuring device, and an optical SNR of the optical signal is determined by an optical SNR calculation circuit based on a measured value of the degree of polarization.

Abstract: Described is a method and system for reducing system penalty from polarization mode dispersion. The method includes receiving a plurality of signals at a receiving end of a transmission line, each signal being received on one of a plurality of channels of the transmission line and measuring a signal degradation of at least one of the channels of the transmission line. An amount of adjustment of a polarization controller is determined based on the signal degradation, the amount of adjustment being selected to reduce the polarization mode dispersion. The amount of adjustment is then transmitted to the polarization controller.

Abstract: In order to reduce mutual interferences between POLMUX and signals, the signals are transmitted with differed to each other carrying signals, thereby making it possible to obtain the circular polarization of each resulting POLMUX signal. Each second POLMUX signal is transmissible with an opposite circular polarization. In order to reduce also interferences when only one modulated data signal is transmitted through a POLMUX channel, a polarization plane of modulated data signals of each second POLMUX channel is turned at 45°. In a variant, polarization multiplex signals are produces and the resulting polarizations thereof in adjacent channels are perpendicular to each other.

Abstract: A method, apparatus and system for providing clock and data recovery in a receiver for receiving a high speed coherent polarization division multiplexed optical signal using a digital signal processing block including a spectral domain spatial combiner are provided.

Abstract: The polarization direction of an optical signal is changed by a polarization controller so as to be orthogonal to a main axis of a polarizer. A control pulse generator generates control pulses from control beam with a wavelength which is different from the wavelength of the optical signal. The optical signal and the control pulse are input to a nonlinear optical fiber. In the nonlinear optical fiber, the optical signal, during a time period in which the optical signal and the control pulse coincide, is amplified with optical parametric amplification around a polarization direction of the control pulse. The optical signal, during the time period in which the optical signal and the control pulse coincide, passes through the polarizer.

Abstract: Methods and apparatus are provided for transmitting alternate-polarization phase-shift-keyed data. The output of a laser is modulated to optically encode electronic data using phase shift keying (PSK) to generate an optical signal. An alternate polarization PSK (APol-PSK) signal is generated by alternating the polarization of the optical signal using a modulator such that successive optical bits have substantially orthogonal polarizations.

Abstract: The present invention relates an optical waveform measuring apparatus designed to eliminate the polarization dependency of an intensity correlation signal without a polarization diversity arrangement. The apparatus comprises a sampling light outputting unit for outputting a sampling light pulse to sample light under measurement, a sampling result outputting unit for developing a nonlinear optical effect stemming from the light under measurement and the sampling light pulse from the sampling light outputting unit to output light corresponding to a result of the sampling of the light under measurement, and a polarization state control unit for, before the start of the measurement of the light under measurement, carrying out control on the basis of a power level of the light from the sampling result outputting unit so that a polarization state of the light under measurement, which is to be inputted to the sampling light output unit, is placed into a predetermined state.

Abstract: An optical communication system is provided. In one embodiment, a source creates a multiplicity of photon pairs, with each photon pair comprising a first photon and a second photon. The first photon is sent to a transmitter, and either remains in the transmitter or is transmitted by the transmitter to a receiver. The second photon is sent to the receiver. Data is decoded by determining a polarization direction and a time of detection of any photon pairs detected at the receiver.

Abstract: An optical transmission system includes an optical transmitter that includes first and second light sources, first and second phase modulators respectively modulating light from the first and the second light sources, and a polarized beam combiner combining the light output from the first and the second phase modulators to output an optical signal; and an optical receiver that includes a local oscillator, a polarization beam splitter splitting, according to polarization, the optical signal transmitted from the optical transmitter, and first and second digital coherent receivers corresponding to the first and the second phase modulators, and including a frontend that mixes light from the local oscillator and the polarization-split optical signal to output an electrical signal of real and imaginary parts, an analog-digital converting unit converting the electrical signal to a digital signal, and a digital signal processing unit estimating phase of the digital signal and extracting a signal.

Abstract: Methods and apparatus are provided for optical polarization mode dispersion compensator (PMDC) feedback control for APol-DPSK signals. A feedback signal generator includes a delay-line-interferometer (DLI), with a differential delay line delay (D) different from one bit period (Tb). In an exemplary embodiment, the DLI delay is in the range of 0.5 Tb<D<1.0 Tb, or 1.0 Tb<D<1.5 Tb, preferably 0.85 Tb or 1.15 Tb. The DLI is coupled to a single-ended detector, whose output is amplified and bandpass filtered around the frequency of half the bit rate. The filtered signal is then applied to an RF power detector to generate the PMDC feedback signal. Generation of the PMDC feedback signal in accordance with the present invention is insensitive to any alignment of the state of polarization (SOP) of the received APol-DPSK signal with the principal state of polarization (PSP) of the transmission link. As a result, there is no need for a polarization scrambler at the transmitter.

Abstract: Photonic signals are tagged with a pre-selected modification, such as a polarization signature to carry data across an obstructed path between sender and receiver. Communication authentication through polarization variation allows for Yuen-Kumar or entangled photon quantum communication protocols to propagate through environmental scattering media such as air, smoke, fog, rain, and water. While ultraviolet light photons are well suited as a carrier for quantum communication signals scattered in air, it is appreciated that visible wavelengths have longer propagation paths in water to convey non-line-of-sight data. A secure signal is scattered by the media and simultaneously communicated to a single recipient or multiple recipients exposed to scattered signal portions. A process of solving the scattering processes through a random scattering media is provided to reconstruct a quantum keyed message at a receiver.

Abstract: Multilevel soft-equalizer detectors, such as a maximum a posteriori probability (MAP) detector, suitable for use in polarization multiplexed optical communications using multilevel modulations and coherent detection are disclosed. Detection systems and methods may consider two symbols transmitted over two orthogonal polarization states as a two-component symbol, which is effective in eliminating the bit error ratio (BER) floor phenomenon introduced by conventional soft equalizers.

Abstract: This application describes devices and techniques for dynamically controlling polarization light at one or more locations along the optical transmission path to reduce optical noise and PMD in the optical signal. One device according to an implementation includes a polarization controller to receive an optical signal and operable to control polarization of the optical signal in response to a control signal, a fixed optical polarizer to receive output from the optical polarization controller and to produce an output optical signal, and a circuit to receive a fraction of the output optical signal from the fixed optical polarizer and operable to produce the control signal in response to an output power level of the output optical signal which controls the polarization controller to maximize the output power level.

Abstract: A polarization mode dispersion (PMD) suppressing apparatus wherein a first polarization controller adjusts a polarization of an input signal, thereby generating a first polarization adjusted signal; a variable DGD compensator gives a DGD to the first polarization adjusted signal, thereby generating a first PMD compensated signal; a second polarization controller adjusts a polarization of the first PMD compensated signal, thereby generating a second polarization adjusted signal; a polarization beam splitter produces a higher-order PMD suppressed signal forming one of two orthogonal components of the second polarization adjusted signal and a monitor signal forming the other component; an intensity detector generates an optical carrier intensity signal reflecting the intensity of an optical carrier wavelength component; and a control signal generator controls the first polarization controller, etc.

Abstract: A method and system for single laser bidirectional links are disclosed and may include communicating a high speed optical signal from a transmit CMOS photonics chip to a receive CMOS photonics chip and communicating a low-speed optical signal from the receive CMOS photonics chip to the transmit CMOS photonics chip via one or more optical fibers. The optical signals may be coupled to and from the CMOS photonics chips utilizing single-polarization grating couplers. The optical signals may be coupled to and from the CMOS photonics chips utilizing polarization-splitting grating couplers. The optical signals may be amplitude or phase modulated. The optical fibers may comprise single-mode or polarization-maintaining fibers. A polarization of the high-speed optical signal may be configured before communicating it over the single-mode fibers. The low-speed optical signal may be generated by modulating the received high-speed optical signal or from a portion of the received high-speed optical signal.

Abstract: First and second transmitted optical waves having orthogonal polarization states are combined in a polarization multiplexed optical wave. At an optical receiver, an electrical field of the polarization multiplexed optical wave is measured. A plurality of polarization states of the polarization multiplexed optical wave is determined from the measured electrical field. From the plurality of polarization states, a transform that aligns the orthogonal polarization states of the first and second transmitted optical waves with respect to principal axes of the optical receiver is estimated. The first and second transmitted optical waves are recovered by applying the transform to one of i) the polarization multiplexed optical wave and ii) the measured electrical field of the polarization multiplexed optical wave.

Abstract: Polarization multiplexing with different differential phase shift keying (DPSK) schemes generally uses DPSK modulated signals modulated using different DPSK modulation schemes and combined with orthogonal polarizations relative to each other. The different DPSK modulation schemes may use different DPSK phase shifts to represent data, such as a regular DPSK modulation scheme and a ?/2 DPSK modulation scheme. By using different DPSK modulation schemes to represent data on the orthogonally polarized signals, the DPSK demodulators may effectively separate the orthogonally polarized signals using the property of the DPSK receivers. To optimize performance, the DPSK modulated signals may also be bit-interleaved when combined with orthogonal polarization.

Abstract: A method and device for reducing the distortion of optical pulses caused by the polarization mode dispersion in optical communication systems is provided. When an optical pulse having any polarization is transmitted through an optical communication system, which is optically anisotropic, at least in sections, the optical pulse may become distorted due to the different velocities of the various polarization components. This distortion of the optical pulses may reduces the maximum transmission rate of the system. A method is provided for functioning in response to the detected transmission quality of the communication system where a polarization-controlling device for setting the polarization of the optical pulse is driven in such a way that the transmission quality is maximized. An optical communication system, including an optical transmission medium, involves a device for determining the transmission quality of the communication system, a regulating device, and a polarization-controlling device.

Abstract: In a coherent optical receiver, a frequency domain engine digitally processes at least two multi-bit sample streams of a received optical signal. The frequency domain engine includes a Fast Fourier Transform (FFT) filter for computing a complex vector representative of a frequency-domain spectrum of the received optical signal. A transpose and add block computes a vector sum of the complex vector and a transposed version of the complex vector, and an Inverse Fast Fourier Transform (IFFT) filter computes a complex output vector from the addition result. With this arrangement, parallel real filter operations are efficiently performed on each of the multi-bit sample streams, using a single back-to-back FFT-IFFT filter structure.