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: A two-pump optical parametric device (OPD) having a nonlinear birefringent fiber, in which various four-wave mixing (FWM) processes can occur. The OPD applies, to the nonlinear birefringent fiber, two pump waves, each polarized at about 45 degrees with respect to a birefringence axis of the fiber, and a polarized input signal. A relevant FWM process couples the pump waves and the signal to cause the fiber to generate a desired output signal. In one configuration, the relevant FWM process is inverse modulational interaction, which causes the desired output signal to be generated through amplification or attenuation of the input signal. In another configuration, the relevant FWM process is phase conjugation, which causes the desired output signal to be generated through amplification of the input signal. In yet another configuration, the relevant FWM process is Bragg scattering, which causes the desired output signal to be generated as a corresponding idler signal.

Abstract: A WDM system having at least two channels, each of which employs two polarizations, is arranged so that the start times of symbols carried by one polarization of a channel are displaced in time from the start times of symbols carried by the other polarization of that channel, e.g., the start time for each symbol on one polarization is not substantially synchronized with the closest-in-time symbol start time on the other polarization of that channel. Preferably, the data signals are modulated using a return-to-zero (RZ) format and the start times of the symbols of the data signal carried by one polarization of a channel is offset from the start time of the symbols data signal carried by the other polarization of that channel by between 20% to 80%—preferably 50%—of the symbol period of the data signals, when the data signals have the same symbol period.

Abstract: Method and apparatus are provided for polarization demultiplexing for a Polarization Division Multiplexed (PDM) signal stream in the optical domain. The optical PDM signal stream includes a first channel representing a first data stream and a second channel representing a second data stream, a time delay between the first channel and the second channel. A Polarization Beam Splitter (PBS) demultiplexes an optical PDM signal into the first channel and the second channel. An associated processing block obtains one of the channels and provides a Polarization Controller with for a control signal corresponding to the power level of the low frequency portion of the RF spectrum of the channel obtained. Based on the control signal, the Polarization Controller adjusts a state of polarization of the optical PDM signal stream that is provided to the PBS for demultiplexing.

Abstract: An arrangement is described for compensating intra-channel nonlinearities in an optical communications system which combines optical dispersion compensation with electronic pre-distortion (EPD). EPD with moderate lookup table size can effectively suppress intra-channel nonlinearities over optical transmission links incorporating optical dispersion compensation. The arrangement can be implemented for a variety of optical communications systems, including 10 Gb/s, 40 Gb/s and higher bit rate systems as well as single-channel and wavelength-division multiplexing (WDM) systems.

Abstract: A two-pump optical parametric device (OPD) having a nonlinear birefringent fiber, in which various four-wave mixing (FWM) processes can occur. The OPD applies, to the nonlinear birefringent fiber, two pump waves, each polarized at about 45 degrees with respect to a birefringence axis of the fiber, and a polarized input signal. A relevant FWM process couples the pump waves and the signal to cause the fiber to generate a desired output signal. In one configuration, the relevant FWM process is inverse modulational interaction, which causes the desired output signal to be generated through amplification or attenuation of the input signal. In another configuration, the relevant FWM process is phase conjugation, which causes the desired output signal to be generated through amplification of the input signal. In yet another configuration, the relevant FWM process is Bragg scattering, which causes the desired output signal to be generated as a corresponding idler signal.

Abstract: An arrangement is described for compensating intra-channel nonlinearities in an optical communications system which combines optical dispersion compensation with electronic pre-distortion (EPD). EPD with moderate lookup table size can effectively suppress intra-channel nonlinearities over optical transmission links incorporating optical dispersion compensation. The arrangement can be implemented for a variety of optical communications systems, including 10 Gb/s, 40 Gb/s and higher bit rate systems as well as single-channel and wavelength-division multiplexing (WDM) systems.

Abstract: A feedback signal indicative of the average RF power of an APol-DPSK optical signal is used by a PMD compensator to adjust the amount of compensation applied to the optical signal.

Abstract: An optical receiver adapted to apply multiple-sampling processing to an optical duobinary signal received over a transmission link in an optical communication system. In one embodiment, the receiver has an optical-to-electrical signal converter coupled to a decoder adapted to process an electrical signal generated by the converter to generate a bit sequence corresponding to the optical signal. To generate a bit value, the decoder first obtains two or more bit estimate values by sampling the electrical signal within a corresponding signaling interval two or more times. The decoder then applies a logical function to the bit estimate values, which produces the corresponding bit value for the bit sequence. Advantageously, embodiments of the present invention improve overall back-to-back (i.e., source-to-destination) system performance, e.g., by reducing the number of decoding errors associated with timing jitter and/or spontaneous beat noise in the received optical signal.

Abstract: For optical communications, apparatus and methods are provided for performing dispersion compensation management that suppresses intra-channel nonlinearities, inter-channel cross-phase modulation (XPM) and/or nonlinear polarization scattering. In optical communication, in which wavelength division multiplexed (WDM) channels are modulated, detecting and measuring channels with coherent detection is complicated due to impairments caused by neighboring channels. Apparatus and methods are provided which reduce the effect of impairments by performing in-line Periodic Group Delay (PGD) dispersion compensation on a WDM signal so as to enable detection of individual channels without severe degradation of system performance. Preferably the PGD dispersion compensator has within a channel a chromatic dispersion substantially similar to a DCF and between channels the group delay is substantially similar.

Abstract: An optical receiver adapted to process an optical duobinary signal received over a transmission link in an optical communication system. In one embodiment, the receiver has an optical-to-electrical signal converter coupled to a decoder. The decoder processes an electrical signal generated by the converter to generate a bit sequence corresponding to the optical signal. To generate a bit value, the decoder integrates the electrical signal using a sampling window and compares the integration result with a decision threshold value. In one configuration, the width of the sampling window and the decision threshold value are selected based on the eye diagram and noise distribution function, respectively, corresponding to the optical signal. Advantageously, embodiments of the present invention improve overall back-to-back (i.e., source-to-destination) system performance, e.g., by improving dispersion tolerance and/or reducing optical power corresponding to a selected bit error rate value.

Abstract: A method and system for ultra-high bit rate fiber-optic communications (e.g., 160 Gb/s) utilize a phase-correlated modulation format where phases of bits in adjacent four-bit groups in transmitted optical pulse trains are altered by ? (or 180°).

Abstract: A self-polarization diversity technique to combat PMD in a direct-detection optical OFDM system. This technique does not require any dynamic polarization control, and can simultaneous compensate PMD in a WDM system with one device. Simulation results show that this technique virtually completely eliminates the PMD impairments in direct-detection optical OFDM systems.

Abstract: The present invention includes apparatus and method of a variable step size dithering control algorithm for polarization mode dispersion controllers (PMDCs). The dithering step size of the PCs is adjusted according to the feedback signal including degree of polarization (DOP).

Abstract: A method and apparatus for dispersion management in hybrid data rate long haul mesh networks are provided. The apparatus comprises a dispersion compensator for fully compensating the residual dispersion of a fiber link in the mesh network. A de-interleaver is coupled to the dispersion compensator for de-interleaving odd and even channels of wavelength division multiplexed (WDM) signals transmitted across the fiber link. A delay device is coupled to the de-interleaver for introducing a delay to the odd channels or the even channels of the WDM signals to decorrelate the odd and even channels and substantially reduce inter-channel cross-phase modulation.

Abstract: An arrangement is described for compensating intra-channel nonlinearities in an optical communications system which combines optical dispersion compensation with electronic pre-distortion (EPD). EPD with moderate lookup table size can effectively suppress intra-channel nonlinearities over optical transmission links incorporating optical dispersion compensation. The arrangement can be implemented for a variety of optical communications systems, including 10 Gb/s, 40 Gb/s and higher bit rate systems as well as single-channel and wavelength-division multiplexing (WDM) systems.

Abstract: A method for selecting an optimum delay length in a polarization mode dispersion (PMD) compensator configured with a constant-length delay line and deployed in an optical communication system. The optimum delay length depends on the data modulation format, bit rate, and/or signal bandwidth and is preferably selected such that outage probability in the communication system is at a minimum. System performance of a PMD compensator configured with a constant-length delay line having the optimum length approaches that of a PMD compensator configured with a variable-length delay line. The method extends the application range of constant-length delay line PMD compensators while reducing the cost of implementing high-performance PMD compensation.

Abstract: A multi-channel (e.g. WDM) receiver, in which l PMD compensators are time-shared by n (n>1) communication channels, where 1?l?n?1. The receiver implements PMD monitoring to identify channels exhibiting relatively high amounts of PMD. Some or all of the identified channels are then subjected, before decoding, to PMD-reduction processing, while the remaining channels are decoded without such processing. Channel allocation for the processing may be changed dynamically depending on the current amounts of PMD exhibited by various channels. Due to efficient utilization of PMD compensators, multi-channel receivers of the invention are capable of performance comparable to that of the corresponding fully compensated (i.e., having a dedicated PMD compensator for each channel) receivers, but at appreciably lower cost.

Abstract: Method and apparatus for transmitting a light signal in an optical transmission system is described. In an example, an optical transmission link includes an input port and an output port. The optical transmission link is configured to propagate optical pulses from the input port to the output port. Information is encoded using phase relationships between adjacent ones of the optical pulses. A phase conjugator is disposed between the input port and the output port. The phase conjugator is positioned to reduce phase variance of the optical pulses at the output port.

Abstract: The present invention includes apparatus and method of a variable step size dithering control algorithm for polarization mode dispersion controllers (PMDCs). The dithering step size of the PCs is adjusted according to the feedback signal including degree of polarization (DOP).