Patent application number | Description | Published |
20090074415 | PMD INSENSITIVE DIRECT-DETECTION OPTICAL OFDM SYSTEMS USING SELF-POLARIZATION DIVERSITY - 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. | 03-19-2009 |
20090324224 | System, method and apparatus to suppress inter-channel nonlinearities in WDM systems with coherent detection - 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. | 12-31-2009 |
20100034541 | PMDC FEEDBACK SIGNAL FOR ALTERNATE POLARIZATION DPSK SYSTEM - 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. | 02-11-2010 |
20100103505 | POLARIZATION-INDEPENDENT FOUR-WAVE MIXING IN A BIREFRINGENT FIBER - 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. | 04-29-2010 |
20100150555 | Automatic polarization demultiplexing for polarization division multiplexed signals - 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. | 06-17-2010 |
20100150559 | Time-interleaved polarization-division-multiplexed transmission systems and transmitters - 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. | 06-17-2010 |
20100247109 | PMDC FEEDBACK ARRANGEMENT FOR APOL-DPSK - 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 Tb09-30-2010 | |
20110052196 | Narrow-band DPSK apparatus, system, method - System, apparatus and methods are provided for optical communication which tolerates the tight filtering effects from concatenation of reconfigurable optical add drop multiplexers (ROADMs). An exemplary system includes a receiver configured to receive a Narrow-Band Differential-Phase-Shift-Keyed (NB-DPSK) optical signal. The receiver includes a Delay Line Interferometer (DLI) with a path length difference of less than approximately one bit period and a detector for detecting DLI output to form an electrical signal. The bandwidth of the NB-DPSK optical signal is less than approximately one-half of a first bit rate of a transmitter from which the NB-DPSK optical signal is received. The electrical signal is processed to decode transmitted data. A corresponding transmitter amplifies a first input signal having a first bit rate; and drives a DPSK modulator after amplification to generate the NB-DPSK optical signal, which has a bandwidth less than approximately one-half of the first bit rate. | 03-03-2011 |
20110142449 | Method And Apparatus For Polarization-Division-Multiplexed Optical Coherent Receivers - The singularity problem of the constant modulus algorithm (CMA) equalizer may be overcome by implementing the CMA equalizer as a two-stage equalizer, with the first stage being a modified version of a CMA equalizer and the second stage being a conventional CMA equalizer. The first stage may be made up of four sub-equalizers, of which only two of the sub-equalizers are independent, i.e., uncorrelated to each other. This first stage equalizer may compensate for PMD. The second stage equalizer is a conventional CMA equalizer made up of four sub-equalizers that are adjusted independently. This second stage equalizer may compensate for polarization-dependent loss (PDL) and any residual CD that is not fully compensated for by a CD compensator before the two-stage equalizer. Advantageously, as the determinant of the first stage never approaches zero, the singularity problem of a conventional CMA single-stage-only equalizer is avoided by the two-stage equalizer. | 06-16-2011 |
20110255879 | Electronic Nonlinearity Compensation For Optical Transmission Systems - Embodiments for optical communication are provided in which a receiver includes a digital signal processor configured to process a digital form of an input signal. In one embodiment, the digital signal processor includes a first electronic chromatic dispersion compensation module for compensating the digital form of the input signal, at least one nonlinearity compensation stage for serially compensating an output of the electronic chromatic dispersion compensation module; and a second electronic chromatic dispersion compensation module for compensating an output of the at least one nonlinearity compensation stage. | 10-20-2011 |
20110280587 | PMD Insensitive Direct-Detection Optical OFDM Systems Using Self-Polarization Diversity - 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. | 11-17-2011 |
20120002283 | METHOD AND APPARATUS FOR RAMAN CO-PUMPS - An example Raman co-pump apparatus includes a control module for controlling output received from at least one of a first laser and a second laser, said output of said first laser and said second laser for combining into a co-pump output, wherein the control module is configured to increase a frequency difference between said first laser and said second laser. The apparatus may also include at least one of a first laser for providing a first output, a second laser for providing a second output and a polarization beam combiner for combining the first and second output into the co-pump output. Spectral overlap of orthogonally polarized pump lasers is avoided via: 1) control of the frequency (wavelength) interleave and the mode spacing of co-pump lasers; 2) control of frequency (wavelength) offset of co-pump lasers to reduce spectral overlap; and 3) use a single co-pump laser with large mode spacing. | 01-05-2012 |
20120002979 | Method And Apparatus For Polarization-Division-Multiplexed Optical Receivers - An optical receiver includes a two-stage constant modulus algorithm (CMA) equalizer. The first stage is a modified version of a CMA equalizer and the second stage is a conventional CMA equalizer. The first stage may be made up of four sub-equalizers, of which only two of the sub-equalizers are independent, i.e., uncorrelated to each other. This first stage equalizer compensates for polarization-mode dispersion (PMD). The second stage equalizer is a conventional CMA equalizer made up of four sub-equalizers that are adjusted independently. This second stage equalizer may compensate for polarization-dependent loss (PDL). The receiver includes a first processor that determines PMD information based on a plurality of transfer function parameters of the modified CMA equalization of the first stage equalizer and the modified-equalized output and a second processor that determines PDL based on a plurality of transfer function parameters of the CMA equalization of the second stage equalizer. | 01-05-2012 |
20120170929 | Apparatus And Method For Monitoring An Optical Coherent Network - An example method determines at an optical network monitoring device whether a value for at least one parameter that characterizes an optical signal which traverses a link of an optical coherent network is above a corresponding threshold and sets an alarm indicator when the value is larger than the corresponding threshold. The at least one corresponding parameter is at least one of polarization mode dispersion, polarization dependent loss and chromatic dispersion. An example method may obtains the optical signal from the link of the coherent optical network and determines the value for the at least one parameter, which may entail calculating the value based on the optical signal and filter coefficients of a filter that can be utilized to compensate the optical signal. In another embodiment, the value for the at least one parameter is received from a monitoring unit that determined the value from the optical signal | 07-05-2012 |
20130071124 | Coherent Optical Receivers For Colorless Reception - One coherent optical receiver includes a 3×3 coupler for receiving a signal and a local oscillator into a first and a third input port respectively, and three detectors for detecting a respective output of the coupler to generate corresponding first, second and third detected signals. A detected signal is filtered by an Alternating Current (AC) coupler to generate a respective first, second or third filtered signal. An adder adds the first, the second and the third filtered signals to determine a directly detected signal term. A first subtractor subtracts the directly detected signal term from the first filtered signal to determine an in-phase signal. A second subtractor subtracts the directly detected signal term from the third filtered signal to determine a quadrature signal. A digital signal processor processes the in-phase signal and the quadrature signal to recover the optical signal. | 03-21-2013 |
20130077973 | SPECTRALLY EFFICIENT MODULATION FOR AN OPTICAL-TRANSPORT SYSTEM - An optical transport system having an optical add-drop multiplexer configured to reduce inter-channel crosstalk by driving Mach-Zehnder pulse carvers in its optical transmitters with electrical drive signals whose swing range is smaller than voltage 2V | 03-28-2013 |
20130315532 | OPTICAL TIME DOMAIN REFLECTOMETRY FOR MULTIPLE SPATIAL MODE FIBERS - An apparatus includes an N×1 spatial mode multiplexer, an optical source and an optical receiver. The spatial mode multiplexer has N input ports and an output port end-couplable to a multimode optical fiber. The multiplexer is configured to preferentially couple light between individual ones of the input ports and corresponding spatial optical modes of the multimode optical fiber. The optical source is connected to a first one of the input ports to launch an optical probe pulse into the fiber. The optical receiver is connected to electrically analyze an optical signal backscattered from the multimode optical fiber and output by a second one of the input ports in response to the launch of the optical probe pulse into the fiber. | 11-28-2013 |
20130336649 | ADAPTIVE CONSTELLATIONS AND DECISION REGIONS FOR AN OPTICAL TRANSPORT SYSTEM - An optical transport system in which (i) an optical transmitter is configured to adaptively change an operative constellation to use a constellation that provides optimal performance characteristics for the present optical-link conditions and/or (ii) an optical receiver is configured to change shapes of the decision regions corresponding to an operative constellation to adapt them to the type of signal distortions experienced by a transmitted optical signal in the optical link between the transmitter and receiver. Under some optical-link conditions, the optical receiver might use a decision-region configuration in which a decision region corresponding to a first constellation point includes an area that is closer in distance to a different second constellation point than to the first constellation point. | 12-19-2013 |
20140079394 | Optical Communication Of Interleaved Symbols Associated With Polarizations - An apparatus comprises a coherent optical transmitter. The coherent optical transmitter comprises a first modulator for generating a first polarization, a second modulator for generating a second polarization, and a symbol interleaver configured to receive a first symbol stream intended to be transmitted on a first polarization and a second symbol stream intended to be transmitted on a second polarization, to direct one portion of symbols of the first symbol stream to the first modulator for modulation onto the first polarization and another portion of the symbols of the first symbol stream to the second modulator for modulation onto the second polarization, and to direct one portion of symbols of the second symbol stream to the first modulator for modulation onto the first polarization and another portion of the symbols of the second symbol stream to the second modulator for modulation onto the second polarization. | 03-20-2014 |
20140086594 | OPTICAL RECEIVER HAVING A SIGNAL-EQUALIZATION CAPABILITY - In one embodiment, an optical receiver has a bulk dispersion compensator and a butterfly equalizer serially connected to one another to perform dispersion-compensation processing and electronic polarization de-multiplexing. The bulk dispersion compensator has a relatively large dispersion-compensation capacity, but is relatively slow and operates in a quasi-static configuration. The butterfly equalizer has a relatively small dispersion-compensation capacity, but can be dynamically reconfigured on a relatively fast time scale to track the changing conditions in the optical-transport link. The optical receiver has a feedback path that enables the configuration of the bulk dispersion compensator to be changed based on the configuration of the butterfly equalizer in a manner that advantageously enables the receiver to tolerate larger amounts of chromatic dispersion and/or polarization-mode dispersion than without the use of the feedback path. | 03-27-2014 |
20140241722 | PDM-(M) Ask Optical Systems And Methods For Metro Network Applications - An apparatus, e.g. an optical communication system, includes an optical transmitter and an optical receiver. The transmitter includes a laser configured to provide an optical signal amplitude-modulated among M different levels, e.g. in two polarizations. The receiver is configured to demodulate the optical signal to produce a received symbol constellation including a plurality of symbol rings in a complex I-Q space. | 08-28-2014 |
20150086200 | Space To Wavelength Superchannel Conversion - An apparatus inputs an input configured to receive an input optical signal, and an output configured to output an output optical signal. A superchannel converter is coupled between the input and the output. The superchannel converter is configured to convert N spatial modes of the input optical signal to M spatial modes of the output optical signal. | 03-26-2015 |
20150086216 | Level Spacing For M-PAM Optical Systems With Coherent Detection - An apparatus includes an optical transmitter configured to provide an optical signal amplitude-modulated among M different levels. A constellation control module is configured to provide a drive signal to control the optical signal. A feedback module is configured to receive a measure of spacing between amplitude peaks of a symbol constellation of the optical signal. The feedback module is further configured to regulate the constellation control module to adjust the optical signal in response to the measure of spacing. | 03-26-2015 |