Abstract: An apparatus comprises an optical transmitter that comprises a processor and at least one optical modulator. The processor is configured to generate electronic representations of at least two pre-dispersion-compensated phase-conjugated optical variants carrying a same modulated payload data for transmission. The at least one optical modulator is configured to modulate the electronic representations, wherein an amount of dispersion induced on the pre-dispersion-compensated phase-conjugated optical variants depends on an accumulated dispersion (AD) of a transmission link through which the pre-dispersion-compensated phase-conjugated optical variants are to be transmitted. The amount of dispersion induced on the phase-conjugated optical variants may be approximately ?AD/2, where AD is the accumulated dispersion of the transmission link.

Abstract: An apparatus receives data encoded in a format where information bits for transmission are mapped into symbols each carrying a plurality of bits, some of which are encoded through a frequency-shift keyed (FSK) format and the rest of which are encoded through an additional modulation format on at least one FSK carrier. The receiver detects the signal through a dual-polarization coherent receiver front-end, and recovers polarization components of the signal by decoding a first non-zero portion of a plurality of bits carried by a symbol based on frequency slot position of at least one FSK carrier in the polarization components and a second non-zero portion of the plurality of bits carried by the symbol based on the additional modulation carried by at least one FSK carrier in the polarization components. Pilot-assisted orthogonal frequency-division de-multiplexing (PA-OFDM) may be used for spectrally-efficient signal reception, even in the presence of severe FSK errors.

Abstract: An apparatus receives data encoded in a format where information bits for transmission are mapped into symbols each carrying a plurality of bits, some of which are encoded through a frequency-shift keyed (FSK) format and the rest of which are encoded through an additional modulation format on at least one FSK carrier. The receiver detects the signal through a dual-polarization coherent receiver front-end, and recovers polarization components of the signal by decoding a first non-zero portion of a plurality of bits carried by a symbol based on frequency slot position of at least one FSK carrier in the polarization components and a second non-zero portion of the plurality of bits carried by the symbol based on the additional modulation carried by at least one FSK carrier in the polarization components. Pilot-assisted orthogonal frequency-division de-multiplexing (PA-OFDM) may be used for spectrally-efficient signal reception, even in the presence of severe FSK errors.

Abstract: An optical transport system configured to transmit at least two phase-conjugated optical variants carrying the same modulated symbols, with the phase-conjugated optical variants in being different from one another in one or more of polarization of light, the time of transmission, spatial localization, optical carrier wavelength, and subcarrier frequency during transmission. The two phase-conjugated optical variants can be generated by a single polarization-diversity transmitter to be orthogonally polarized, and propagate through an optical transmission link with the same wavelength and spatial path. The optical variants are detected and processed at the receiver in a manner that enables coherent summation of the corresponding electrical signals prior to constellation de-mapping.

Abstract: An apparatus comprises an optical transmitter that comprises a processor and at least one optical modulator. The processor is configured to generate electronic representations of at least two pre-dispersion-compensated phase-conjugated optical variants carrying a same modulated payload data for transmission. The at least one optical modulator is configured to modulate the electronic representations, wherein an amount of dispersion induced on the pre-dispersion-compensated phase-conjugated optical variants depends on an accumulated dispersion (AD) of a transmission link through which the pre-dispersion-compensated phase-conjugated optical variants are to be transmitted. The amount of dispersion induced on the phase-conjugated optical variants may be approximately ?AD/2, where AD is the accumulated dispersion of the transmission link.

Abstract: An optical line card system includes one or more input interfaces for receiving information, a line interface comprising a plurality of line transponders, and a multiplexer for multiplexing output of the one or more input interfaces onto the plurality of line transponders. The one or more input interfaces have an aggregate information rate RC. The plurality of line transponders have an aggregate information rate RL that is less than or approximately equal to the aggregate information rate RC of the one or more of client interfaces. Each of the line transponders employs a modulation format with a spectral efficiency that enables transmission with at most one opto-electronic regeneration point per link to an end point for electronic routing or switching. Each of the plurality of line transponders is configured to insert output on a respective one of a plurality of orthogonally parallel transmission paths.

Abstract: A method of multiple-band switching using a multi-pump fiber parametric switch is demonstrated. The switching architecture combines parametric band amplification, wavelength conversion and selective signal conjugation, enabled by temporal control of at least one pump of the multi-pump parametric device. The switching speed of the present invention is limited by the rise time of the controlled pump(s).

Abstract: Apparatus and methods are provided for receiving differential phase-shift keyed (DPSK) optical signals subjected to tight optical filtering, such as may be experienced by 40 Gb/s and 100 Gb/s channels in a dense wavelength division multiplexing (DWDM) communications system with 50 GHz channel spacing. An optical DPSK receiver is described which employs an optical delay interferometer (ODI) demodulator having a free spectral range (FSR) that is larger than the symbol rate (SR) of the DPSK signal to be demodulated. The receiver includes means for introducing an additional power imbalance between the outputs of the ODI demodulator, and the additional power imbalance may be related to the ratio of FSR to SR. The additional power imbalance increases the signal tolerance to tight optical filtering, thereby achieving high spectral efficiency in applications such as DWDM.

Abstract: A multi-channel optical equalizer for intersymbol interference mitigation compensates for single- or multi- wavelength channels simultaneously and requires few adjustable parameters. The optical equalizer compensates for overshoots and signal transition degradations in semiconductor optical amplifiers. The equalizer unit uses one control signal for magnitude and one to control signal phase. The equalizer includes a controllable coupling ratio coupler for splitting the light into two portions and a controllable interferometer having two arms, one arm having an additional delay which is equal to an integer multiple of 1/&Dgr;f, where &Dgr;f is the channel spacing between adjacent wavelengths utilized in the optical system. The controllable interferometer has a controllable delay in a first or second arm for adjusting the relative phase of the light passing therethrough. A coupler combines the two signal portions from the first and second arms to form the equalized output signal.

Abstract: An improved multi-channel optical equalizer method and apparatus for intersymbol interference mitigation compensates for single- or multi-wavelength channels simultaneously and requires few adjustable parameters. The optical equalizer can also compensate for overshoots and signal transition degradations of a semiconductor optical amplifier. The equalizer unit has only two control signals, one to control signal magnitude and one to control signal phase, yet it can still compensate many wavelength channels simultaneously. The equalizer includes a coupler with a controllable coupling ratio for splitting the light into two portions and a controllable interferometer means having two arms, one arm having an additional delay which is equal to an integer multiple of 1/&Dgr;f, where &Dgr;f is the channel spacing between adjacent wavelengths utilized in the optical system.

Abstract: An improved multi-channel optical equalizer method and apparatus for intersymbol interference mitigation compensates many wavelength channels simultaneously and requires few adjustable parameters. The equalizer unit has only two control signals, one to control signal magnitude and one to control signal phase, yet it can still compensate many wavelength channels simultaneously. The equalizer includes a coupler with a controllable coupling ratio for splitting the light into two portions and a controllable interferometer means having two arms, one arm having an additional delay which is equal to an integer multiple of 1/&Dgr;f, where &Dgr;f is the channel spacing of the multiwavelength system. The controllable interferometer unit also has a controllable delay in a first or second arm for adjusting the relative phase of the light passing therethrough. A coupler combines the two signal portions from the first and second arms to form the equalized output signal.

Abstract: An optical transmission system exploits the reduced signal-to-noise (SNR) requirements for low-bit rate channels to devise a new wavelength channel allocation scheme which increases the number of channels that a WDM system can support. Wavelengths of low-bit rate channels are assigned outside a flat-gain window (i.e., flat-passband region) of the system. The channel allocation scheme uses the high-bit rate channels located in the flat-passband region of wavelengths and the lower-bit rate channels located outside this passband region with progressively lower-bit rate channels located farther outside this passband region. Low-bit rate channels are also assigned to region(s) of the passband where the non-linear threshold power level of the system may be exceeded.

Abstract: An optical transmission system exploits the reduced signal-to-noise (SNR) requirements for low-bit rate channels to devise a new wavelength channel allocation scheme which increases the number of channels that a WDM system can support. Wavelengths of low-bit rate channels are assigned outside a flat-gain window (i.e., flat-passband region) of the system. The channel allocation scheme uses the high-bit rate channels located in the flat-passband region of wavelengths and the lower-bit rate channels located outside this passband region with progressively lower-bit rate channels located farther outside this passband region. Low-bit rate channels are also assigned to region(s) of the passband where the non-linear threshold power level of the system may be exceeded.

Abstract: An optical transmission system exploits the reduced signal-to-noise (SNR) requirements for low-bit rate channels to devise a new wavelength channel allocation scheme which increases the number of channels that a WDM system can support. Wavelengths of low-bit rate channels are assigned outside a flat-gain window (i.e., flat-passband region) of the system. The channel allocation scheme uses the high-bit rate channels located in the flat-passband region of wavelengths and the lower-bit rate channels located outside this passband region with progressively lower-bit rate channels located farther outside this passband region. Low-bit rate channels are also assigned to region(s) of the passband where the non-linear threshold power level of the system may be exceeded.

Abstract: Phase shift keying (PSK) or differential phase shift keying (DPSK) used as the coding scheme in a high bit rate, long haul dispersion-managed optical transmission system, in which the signaling format is RZ. The system can combine multiple individual channels with different wavelengths in a WDM or dense wavelength division multiplexed (DWDM) arrangement. Dispersion management can be provided using several techniques, such as by using dispersion managed solitons, quasi-linear transmission or conventional RZ transmission with pre-compensation and post-compensation.

Abstract: Substantially error-free communications is achieved in an optical communication system that includes optical amplifiers by detecting bits transmitted in the amplified optical signal using a detection threshold that is derived as a function of a maximum power level associated with a first bit value, e.g., bit “0”, and a minimum power level associated with a second bit value, e.g., bit “1”. Importantly, this detection scheme can be used to accurately detect bit patterns in the amplified signal even in the presence of nonlinear distortions caused by gain variations, such as inter-modal distortion and saturation induced crosstalk. In a wavelength division multiplexed (WDM) system comprising semiconductor optical amplifiers, for example, the detection threshold can be set at a level corresponding to PTOTAL/2N, where PTOTAL represents the total power in the WDM signal and N represents the number of optical channels in the WDM signal.

Abstract: Resonances in cross-phase-modulation (CPM) impairment occur in wavelength-division-multiplexed (WDM) transmission systems, having multiple equal dispersion-length amplifier spans, when channels have an integral number of bit walk-throughs per amplifier span. The CPM resonances are reduced by mis-matching the amplifier span lengths (and/or dispersion in each span) so an integral number of bit walk-throughs do not occur in successive amplifier spans. The CPM resonances are reduced by adding different lengths of dispersion-compensating fiber to each span, using different modulation bit rates and/or clock phase delay for each channel, and using different wavelength-selective clock phase delays for each channel.

Abstract: An apparatus and method for wavelength-division multiplexing employing an arrayed waveguide router and polarization-maintaining input fibers for coupling channels which experience four photon mixing to the router. The invention is useful in extremely dense wavelength-division multiplexing to reduce optical non-linearity.

Abstract: A high-capacity optical fiber network [100, 200] includes wavelength-division multiplexing (WDM) within the 1.4 micron (&mgr;m) wavelength region (i.e., 1335-1435 nm). Such a system includes optical fiber [130] whose peak loss in the 1.4 &mgr;m region is less than its loss at 1310 nm. The optical fiber has a zero dispersion wavelength (&lgr;0) at about 1310 nm, and linear dispersion between about 1.5 and 8.0 ps/nm-km within the 1.4 &mgr;m region. At least three WDM channels operate at 10 Gb/s in the 1.4 &mgr;m wavelength region and have a channel separation of 100 GHz. In one illustrative embodiment of the invention, a broadcast television channel, having amplitude modulated vestigial sideband modulation, simultaneously operates in the 1.3 &mgr;m region (i.e., 1285-1335 nm) and/or the 1.55 &mgr;m region (i.e., 1500-1600 nm). In another embodiment of the invention, 16 digital data channels are multiplexed together in the 1.55 &mgr;m region, each channel operating at about 2.5 Gb/s.