Patents by Inventor Chandrasekhar Sethumadhavan
Chandrasekhar Sethumadhavan has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).
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Patent number: 8594515Abstract: An optical phase conjugator that can be deployed within a long-haul fiber-optic link of an optical WDM system to improve the system's tolerance to intra- and inter-channel nonlinear effects. In one embodiment, the optical phase conjugator has a digital signal processor configured to perform, in the digital electrical domain, a phase-conjugation transformation for various components of a WDM signal so that certain signal distortions imposed on that signal in the front portion of the fiber-optic link are reduced in the back portion of the link. Advantageously, the optical phase conjugator is flexibly configurable to employ an input-to-output carrier-frequency-mapping configuration that is most beneficial under particular operating conditions. mapping configuration that is most beneficial under particular operating conditions.Type: GrantFiled: March 3, 2011Date of Patent: November 26, 2013Assignee: Alcatel LucentInventors: Xiang Liu, Chandrasekhar Sethumadhavan, Robert W. Tkach
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Publication number: 20130236175Abstract: A space division multiplexed (SDM) transmission system that includes at least two segments of transmission media in which a spatial assignment of the two segments is different is provided. For example, the SDM transmission may include a first segment of transmission media having a first spatial assignment and a second segment of transmission media having a second spatial assignment, wherein the first spatial assignment differs from the second spatial assignment. An example method obtains an optical signal on a first segment of transmission media having a first spatial assignment and forwards the optical signal on a second segment of transmission media with a different spatial assignment. The transmission media may be a multi-core fiber (MCF), a multi-mode fiber (MMF), a few-mode fiber (FMF), or a ribbon cable comprising nominally uncoupled single-mode fiber (SMF).Type: ApplicationFiled: September 4, 2012Publication date: September 12, 2013Inventors: Chandrasekhar Sethumadhavan, Xiang Liu, Peter J. Winzer, Alan H. Gnauck
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Patent number: 8515286Abstract: A coherent optical receiver for a data-frame format in which a data frame has two or more pilot-symbol blocks, each having a cyclic prefix or suffix, and one or more payload-symbol blocks, each of which is concatenated with at least one adjacent block without a guard interval between them. The receiver uses optical signals corresponding to the pilot-symbol blocks to perform data-frame synchronization, frequency-offset correction, and channel-estimation procedures, which are robust even in the presence of certain transmission impairments. The receiver applies block-overlap processing with a sliding window to recover the payload data in a manner that substantially cancels the adverse effects of inter-block interference caused by the absence of guard intervals in the payload portion of the data frame.Type: GrantFiled: December 10, 2010Date of Patent: August 20, 2013Assignee: Alcatel LucentInventors: Xiang Liu, Chandrasekhar Sethumadhavan
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Patent number: 8483575Abstract: Frequency-locked optical comb sources are provided that utilize recirculating frequency shifting based on frequency conversion in a modulator, together with a filter. The filter may be a wavelength notch filter and include a plurality of notches. An example apparatus includes a coupler, an I/Q modulator, and a filter. A first input of the coupler receives a first input optical carrier having a first frequency, and a second input of the coupler re receives a set of frequency-shifted carriers from the filter. The input optical carrier may have a plurality of frequencies. The I/Q modulator shifts the frequency of a first output of the coupler. The filter filters modulated output from the I/Q modulator thereby limiting the frequency-shifted carriers to be within an optical bandwidth. A second output of the coupler provides a plurality of frequency-locked carriers containing the first input optical carrier and the set of frequency-shifted carriers.Type: GrantFiled: January 11, 2010Date of Patent: July 9, 2013Assignee: Alcatel LucentInventors: Xiang Liu, Chandrasekhar Sethumadhavan, Robert William Tkach
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Publication number: 20130170841Abstract: Methods and apparatus for power-efficiently and reliably transmitting high-level quadrature amplitude modulation (QAM) optical signals using binary drive signals. Even though binary signals are used to drive a QAM modulator directly, without digital-to-analog conversion, the methods and apparatus disclosed allow the transmission of pilot symbol sequences having near optimal properties, such as a constant power profile in the time domain; a mean power that is approximately the same as the mean power of the data symbols; and roughly uniform amplitude in the frequency domain for non-zero frequency components of the pilot symbol sequence. The binary drive signals can be processed so that the modulated optical signals are selectively constrained to a subset of points of the QAM constellation to form a QAM constellation with reduced size and a mean power that is approximately the same as the mean power of the original QAM constellation.Type: ApplicationFiled: December 30, 2011Publication date: July 4, 2013Applicant: ALCATEL-LUCENT USAInventors: Xiang LIU, Chandrasekhar SETHUMADHAVAN
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Publication number: 20130136449Abstract: An example apparatus comprises an optical transmitter which includes a first processor and at least two optical modulators. The first processor is configured to generate a first electronic representation for each of at least two optical signals for carrying payload data modulated according to a one-dimensional (1-D) modulation format, and to induce on respective ones of the first electronic representations an amount of dispersion that depends on a power-weighted accumulated dispersion (ADPW) of a transmission link through which the at least two optical signals are to be transmitted thereby generating complex-valued electronic representations of pre-dispersion-compensated optical signals. Each of the at least two optical modulators modulate a respective analog version corresponding to a respective one of the complex-valued electronic representations onto a polarization of an optical carrier.Type: ApplicationFiled: December 31, 2012Publication date: May 30, 2013Inventors: Xiang Liu, Peter J. Winzer, Andrew R. Chraplyvy, Robert W. Tkach, Chandrasekhar Sethumadhavan
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Publication number: 20120224855Abstract: An optical phase conjugator that can be deployed within a long-haul fiber-optic link of an optical WDM system to improve the system's tolerance to intra- and inter-channel nonlinear effects. In one embodiment, the optical phase conjugator has a digital signal processor configured to perform, in the digital electrical domain, a phase-conjugation transformation for various components of a WDM signal so that certain signal distortions imposed on that signal in the front portion of the fiber-optic link are reduced in the back portion of the link. Advantageously, the optical phase conjugator is flexibly configurable to employ an input-to-output carrier-frequency-mapping configuration that is most beneficial under particular operating conditions.Type: ApplicationFiled: March 3, 2011Publication date: September 6, 2012Applicant: ALCATEL-LUCENT USA INC.Inventors: Xiang Liu, Chandrasekhar Sethumadhavan, Robert W. Tkach
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Publication number: 20120177372Abstract: Return To Zero (RZ) shaping is performed for a first I/Q modulator whose output corresponds to a first polarization component using a first two digital-to-analog convertors (DACs), each of which is sampled at approximately twice a modulation symbol rate or more and has an output with a first interleaving order that interleaves one of a first pair of intended drive signal patterns and zeros. RZ shaping is also performed for a second I/Q modulator whose output corresponds to a second polarization component using a second two DACs, each sampled at approximately twice the modulation symbol rate or more and having a second interleaving order that interleaves zeros and one of a second pair of intended drive signal patterns, the second interleaving order opposite the first interleaving order. The first polarization and the second polarization may be combined, thereby forming an Interleaved Return To Zero (IRZ) Polarization Division Multiplexed (PDM) signal.Type: ApplicationFiled: January 6, 2011Publication date: July 12, 2012Inventors: Xiang Liu, Chandrasekhar Sethumadhavan
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Publication number: 20120148255Abstract: In one embodiment, an optical transmission system transmits data using a format according to which a data frame has two or more pilot-symbol blocks, each having a guard interval, and two or more payload-symbol blocks that are concatenated without a guard interval between them. The use of guard intervals in the pilot-symbol blocks helps the synchronization and channel-estimation procedures performed at a receiver of the optical transmission system to be robust in the presence of certain transmission impairments. The absence of guard intervals in the payload-symbol blocks helps to minimize the transmission overhead and thus achieve relatively high payload-data throughput.Type: ApplicationFiled: December 10, 2010Publication date: June 14, 2012Applicant: ALCATEL-LUCENT USA INC.Inventors: Xiang Liu, Chandrasekhar Sethumadhavan
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Publication number: 20120148264Abstract: A coherent optical receiver for a data-frame format in which a data frame has two or more pilot-symbol blocks, each having a cyclic prefix or suffix, and one or more payload-symbol blocks, each of which is concatenated with at least one adjacent block without a guard interval between them. The receiver uses optical signals corresponding to the pilot-symbol blocks to perform data-frame synchronization, frequency-offset correction, and channel-estimation procedures, which are robust even in the presence of certain transmission impairments. The receiver applies block-overlap processing with a sliding window to recover the payload data in a manner that substantially cancels the adverse effects of inter-block interference caused by the absence of guard intervals in the payload portion of the data frame.Type: ApplicationFiled: December 10, 2010Publication date: June 14, 2012Applicant: ALCATEL-LUCENT USA INC.Inventors: Xiang Liu, Chandrasekhar Sethumadhavan
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Patent number: 8180227Abstract: Embodiments for optical communication are provided in which subbands of a multi-carrier optical signal are digital coherent detected and then processed to recover data carried by the modulated carriers corresponding to at least one of the subbands. An exemplary optical communication system includes a multi-carrier coherent optical receiver for receiving a multi-carrier optical signal having M modulated carriers that are frequency locked, wherein M is greater than 2. The multi-carrier coherent optical receiver includes a subband digital coherent detector configured to provide output signals in a digital form for N different subbands of the multi-carrier optical signal, where N is an integer greater than 1 and less than M; and a digital signal processor configured to process the digital form of the detected output signals in order to recover the data carried by the modulated carriers corresponding to at least one of the subbands of the multicarrier optical signal.Type: GrantFiled: September 23, 2009Date of Patent: May 15, 2012Assignee: Alcatel LucentInventors: Xiang Liu, Chandrasekhar Sethumadhavan, Robert William Tkach
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Publication number: 20120057863Abstract: In one embodiment, a coherent optical receiver has a digital signal processor that processes one or more digital I/Q-signal pairs to recover data carried by a modulated optical signal in a manner that mitigates, based on calibration data retrieved from a memory or on appropriate performance measures and feedback mechanisms, the detrimental effects of frequency-dependent imbalances between the I and Q sub-channels of at least one of the I/Q channels of the receiver. In various embodiments, the calibration data can be generated and written into the memory at the fabrication facility or in situ while the receiver is being operated in a calibration mode. Alternatively or in addition, the calibration data can be generated and dynamically adjusted online during normal operation of the receiver.Type: ApplicationFiled: September 7, 2010Publication date: March 8, 2012Applicant: ALCATEL-LUCENT USA INC.Inventors: Peter J. Winzer, Xiang Liu, Chandrasekhar Sethumadhavan, Alan H. Gnauck
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Patent number: 8121494Abstract: 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.Type: GrantFiled: August 19, 2008Date of Patent: February 21, 2012Assignee: Alcatel LucentInventors: Chraplyvy R Andrew, Xiang Liu, Chandrasekhar Sethumadhavan
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Publication number: 20120002283Abstract: 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.Type: ApplicationFiled: June 30, 2010Publication date: January 5, 2012Inventors: Chongjin Xie, Chandrasekhar Sethumadhavan, Robert William Tkach
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Publication number: 20110170873Abstract: Frequency-locked optical comb sources are provided that utilize recirculating frequency shifting based on frequency conversion in a modulator, together with a filter. The filter may be a wavelength notch filter and include a plurality of notches. An example apparatus includes a coupler, an I/Q modulator, and a filter. A first input of the coupler receives a first input optical carrier having a first frequency, and a second input of the coupler re receives a set of frequency-shifted carriers from the filter. The input optical carrier may have a plurality of frequencies. The I/Q modulator shifts the frequency of a first output of the coupler. The filter filters modulated output from the I/Q modulator thereby limiting the frequency-shifted carriers to be within an optical bandwidth. A second output of the coupler provides a plurality of frequency-locked carriers containing the first input optical carrier and the set of frequency-shifted carriers.Type: ApplicationFiled: January 11, 2010Publication date: July 14, 2011Inventors: Xiang Liu, Chandrasekhar Sethumadhavan, Robert William Tkach
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Publication number: 20110069975Abstract: Embodiments for optical communication are provided in which subbands of a multi-carrier optical signal are digital coherent detected and then processed to recover data carried by the modulated carriers corresponding to at least one of the subbands. An exemplary optical communication system includes a multi-carrier coherent optical receiver for receiving a multi-carrier optical signal having M modulated carriers that are frequency locked, wherein M is greater than 2. The multi-carrier coherent optical receiver includes a subband digital coherent detector configured to provide output signals in a digital form for N different subbands of the multi-carrier optical signal, where N is an integer greater than 1 and less than M; and a digital signal processor configured to process the digital form of the detected output signals in order to recover the data carried by the modulated carriers corresponding to at least one of the subbands of the multicarrier optical signal.Type: ApplicationFiled: September 23, 2009Publication date: March 24, 2011Inventors: Xiang Liu, Chandrasekhar Sethumadhavan, Robert William Tkach
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Publication number: 20100215374Abstract: Systems, apparatus and method for modulating digital data onto an optical carrier to produce a modulated optical carrier in which symbol-modulated optical signals of orthogonal polarizations are temporally interleaved and adapted to be processed by electronic time-division demultiplexing to recover the digital data modulated onto the orthogonal polarizations of the optical signals.Type: ApplicationFiled: February 25, 2010Publication date: August 26, 2010Inventors: Xiang Liu, Chandrasekhar Sethumadhavan
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Publication number: 20100046948Abstract: 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.Type: ApplicationFiled: August 19, 2008Publication date: February 25, 2010Inventors: Andrew Roman Chraplyvy, Xiang Liu, Chandrasekhar Sethumadhavan
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Publication number: 20090086215Abstract: An apparatus and method for detecting a PMUX multilevel DPSK signal having at least two polarization components with equal symbol periods, which comprises utilizing two polarization-independent Optical Delay Interferometers (ODIs), detecting the four outputs of the two ODIs with two balanced detectors, and digitizing the two detected electronic signals at a sampling rate of twice the symbol rate of the said polarization component signals.Type: ApplicationFiled: September 30, 2007Publication date: April 2, 2009Inventors: Xiang Liu, Chandrasekhar Sethumadhavan