Abstract: An amplified optical link having a fault-protection capability that is based, at least in part, on the ability to selectively and independently power up and down different groups of optical amplifiers within the link. In an example embodiment, the optical link is implemented using an optical fiber cable having an electrical power line and arrays of optical amplifiers connected between successive optical fiber segments to form a plurality of disjoint groups of parallel optical paths between the ends of the optical fiber cable. The electrical power line is operable to selectively power, as a group, the optical amplifiers of at least some of the disjoint groups. In various embodiments, different optical paths can be implemented using different respective strands of a single-core optical fiber, different respective cores of a multi-core optical fiber, and/or different respective sets of spatial modes of a multimode optical fiber.

Abstract: A communication system in which probabilistic signal shaping and FEC coding are jointly applied in a manner that enables the use of substantially any constellation template, e.g., a template in which the constellation symbols include a constellation symbol of zero amplitude and/or are arranged in an asymmetric manner. In an example embodiment, the transmitter's electronic encoder can be configured to apply two different respective shaping codes to the information bits and to the corresponding parity bits. The resulting shaped streams can then be appropriately multiplexed and transmitted over the optical communication channel to realize a significant shaping gain. Advantageously, the constellation template(s), two distribution matchers, and FEC code can be flexibly selected and/or adapted to achieve nearly optimal system operation under substantially arbitrary (e.g., arbitrarily bad) channel conditions.

Abstract: A self-coherent optical data receiver configured to use direct detection of optical signals that is compatible with full (amplitude/phase) electric-field reconstruction. To enable the latter, the direct-detected optical signal includes CW light whose carrier frequency is spectrally aligned with a roll-off edge of the data-modulated portion of the signal. In an example embodiment, the receiver may employ two digital filters placed upstream and downstream, respectively, of the field-reconstruction circuit. The upstream filter is configurable to at least partially cancel the effects of SSBI caused by the direct detection. The downstream filter can be configured to perform electronic dispersion compensation and/or electronic polarization demultiplexing. In different embodiments, a filter controller may operate to adaptively change the filter coefficients of the upstream filter based on different signals generated within the digital receive chain.

Abstract: A self-coherent optical data receiver configured to use direct detection of optical signals that is compatible with full (amplitude/phase) electric-field reconstruction. To enable the latter, the direct-detected optical signal includes CW light whose carrier frequency is spectrally aligned with a roll-off edge of the data-modulated portion of the signal. In an example embodiment, the receiver may employ two digital filters placed upstream and downstream, respectively, of the field-reconstruction circuit. The upstream filter is configurable to at least partially cancel the effects of SSBI caused by the direct detection. The downstream filter can be configured to perform electronic dispersion compensation and/or electronic polarization demultiplexing. In different embodiments, a filter controller may operate to adaptively change the filter coefficients of the upstream filter based on different signals generated within the digital receive chain.

Abstract: An apparatus includes a polarization beam splitter (PBS) and an optical detector. The PBS is configured to receive a polarized optical signal transported via an optical communication path of an optical network. The detector is configured to receive from the PBS a first polarization component of the optical signal, and to produce a first electrical measure of the first polarization component. A processor is configured to determine a dynamic metric of the optical communication path based at least on the first electrical measure. Some embodiments also include a second detector configured to receive from the PBS a second polarization component of the optical signal. The second detector produces a second electrical measure of the second polarization component, and the processor is configured to determine the dynamic metric based on both the first and second electrical measures.

Abstract: A communication system in which probabilistic signal shaping and FEC coding are jointly applied in a manner that enables the use of substantially any constellation template, e.g., a template in which the constellation symbols include a constellation symbol of zero amplitude and/or are arranged in an asymmetric manner. In an example embodiment, the transmitter's electronic encoder can be configured to apply two different respective shaping codes to the information bits and to the corresponding parity bits. The resulting shaped streams can then be appropriately multiplexed and transmitted over the optical communication channel to realize a significant shaping gain. Advantageously, the constellation template(s), two distribution matchers, and FEC code can be flexibly selected and/or adapted to achieve nearly optimal system operation under substantially arbitrary (e.g., arbitrarily bad) channel conditions.

Abstract: An optical WDM system configured to use direct detection of communication signals that is compatible with electronic CD compensation on a per-channel basis. In an example embodiment, to enable full (e.g., amplitude and phase) electric-field reconstruction at the receiver, the optical WDM system uses a carrier-frequency plan according to which the carrier-frequency comb used at one end of the WDM link and the carrier-frequency comb used at the other end of the WDM link are offset with respect to one another by one half of the bandwidth of an individual WDM component transmitted therethrough. This frequency offset places each local carrier frequency at a roll-off edge of the corresponding incoming data-modulated signal. As a result, the corresponding combined optical signal beneficially lends itself to direct detection that can be followed by full electric-field reconstruction using a known self-coherent Kramers-Kronig method and then by conventional electronic CD compensation.

Abstract: An amplified optical link having a fault-protection capability that is based, at least in part, on the ability to selectively and independently power up and down different groups of optical amplifiers within the link. In an example embodiment, the optical link is implemented using an optical fiber cable having an electrical power line and arrays of optical amplifiers connected between successive optical fiber segments to form a plurality of disjoint groups of parallel optical paths between the ends of the optical fiber cable. The electrical power line is operable to selectively power, as a group, the optical amplifiers of at least some of the disjoint groups. In various embodiments, different optical paths can be implemented using different respective strands of a single-core optical fiber, different respective cores of a multi-core optical fiber, and/or different respective sets of spatial modes of a multimode optical fiber.

Abstract: An optical line card includes a plurality of coherent receivers and a plurality of optical modulators. The coherent receivers are each configured to receive a corresponding channel of a received optical superchannel. The optical modulators are each configured transmit a corresponding channel of a transmitted optical superchannel. Each of a plurality of optical splitters is configured to receive a corresponding one of a plurality of unmodulated optical signals from an optical source external to the line card. Each splitter directs a first portion of light received by that splitter to a corresponding one of the coherent receivers, and a second portion of light received by that splitter to a corresponding one of said optical modulators.

Abstract: A Raman amplifier having an optical pump configured to generate pump bands, each of which is spectrally aligned with a respective wavelength channel of a frequency grid in a manner that enables the pump bands to coexist in an optical fiber with data-carrying signals of other wavelength channels of the frequency grid without causing unworkable levels of inter-channel interference. In an example embodiment, the optical pump comprises a laser whose single-mode output is modulated to sufficiently suppresses stimulated Brillouin scattering in the optical fiber while still keeping the optical power of each of the resulting pump bands spectrally compact, e.g., substantially contained within the slot width of the respective wavelength channel. In some embodiments, at least some pump bands can be spectrally interleaved with some of the data-carrying signals to increase the data-throughput capacity of the corresponding optical transport system.

Abstract: An apparatus includes a polarization beam splitter (PBS) and an optical detector. The PBS is configured to receive a polarized optical signal transported via an optical communication path of an optical network. The detector is configured to receive from the PBS a first polarization component of the optical signal, and to produce a first electrical measure of the first polarization component. A processor is configured to determine a dynamic metric of the optical communication path based at least on the first electrical measure. Some embodiments also include a second detector configured to receive from the PBS a second polarization component of the optical signal. The second detector produces a second electrical measure of the second polarization component, and the processor is configured to determine the dynamic metric based on both the first and second electrical measures.

Abstract: An optical WDM system configured to use direct detection of communication signals that is compatible with electronic CD compensation on a per-channel basis. In an example embodiment, to enable full (e.g., amplitude and phase) electric-field reconstruction at the receiver, the optical WDM system uses a carrier-frequency plan according to which the carrier-frequency comb used at one end of the WDM link and the carrier-frequency comb used at the other end of the WDM link are offset with respect to one another by one half of the bandwidth of an individual WDM component transmitted therethrough. This frequency offset places each local carrier frequency at a roll-off edge of the corresponding incoming data-modulated signal. As a result, the corresponding combined optical signal beneficially lends itself to direct detection that can be followed by full electric-field reconstruction using a known self-coherent Kramers-Kronig method and then by conventional electronic CD compensation.

Abstract: An apparatus, including: an optical sensor fiber having a first end optically couplable to receive light from a light source, wherein the optical sensor fiber is a multimode optical fiber configured to carry light in different spatial propagating modes, wherein the optical sensor fiber is constructed such that environmental fluctuations couple light energy between some of the spatial propagating modes; a spatial propagating mode demultiplexer optically coupled to a second end the optical sensor fiber and configured to separate a plurality of light signals received from different ones of the spatial propagating modes; and an optical receiver configured to process the separated light signals and to estimate a longitudinal position of one of the environmental fluctuations along the optical sensor fiber based a measured delay between arrival times of the separated light signals.

Abstract: An apparatus includes a polarization beam splitter (PBS) and an optical detector. The PBS is configured to receive a polarized optical signal transported via an optical communication path of an optical network. The detector is configured to receive from the PBS a first polarization component of the optical signal, and to produce a first electrical measure of the first polarization component. A processor is configured to determine a dynamic metric of the optical communication path based at least on the first electrical measure. Some embodiments also include a second detector configured to receive from the PBS a second polarization component of the optical signal. The second detector produces a second electrical measure of the second polarization component, and the processor is configured to determine the dynamic metric based on both the first and second electrical measures.

Abstract: An optical line card includes a plurality of coherent receivers and a plurality of optical modulators. The coherent receivers are each configured to receive a corresponding channel of a received optical superchannel. The optical modulators are each configured transmit a corresponding channel of a transmitted optical superchannel. Each of a plurality of optical splitters is configured to receive a corresponding one of a plurality of unmodulated optical signals from an optical source external to the line card. Each splitter directs a first portion of light received by that splitter to a corresponding one of the coherent receivers, and a second portion of light received by that splitter to a corresponding one of said optical modulators.

Abstract: The outage probability in an under-addressed optical MIMO system may be reduced by configuring a spatial-mode coupler at a transmitter and/or a spatial-mode separator at a receiver to dynamically change its spatial-mode configuration on a time scale that is shorter than the channel coherence time. Provided that the MIMO system employs an FEC code that has a sufficient error-correcting capacity for correcting the amount of errors corresponding to an average state of the MIMO channel established between the transmitter and receiver, this relatively fast dynamic change tends to reduce the frequency of events during which the number of errors per FEC-encoded block of data exceeds the error-correcting capacity of the FEC code.

Abstract: A digital-electronic-to-analog-optical converter, which has a structure consistent with a super-Mach-Zehnder interferometer, and which can perform the functionalities of both a Digital to Analog Converter (DAC) and a digital modulator uses a sub-Mach-Zender modulator to modulate optical wave signals propagating through its optical waveguide in a push-pull manner. The modulation performed is phase modulation realized with electrodes positioned near the optical wave guide where such electrodes carry modulation signals in digital, analog or discrete time signal format creating electromagnetic or electric fields that engage the optical wave signals traveling through the waveguide thus imparting a phase shift onto the optical wave signals. The amount of the phase shift can be implemented through the geometry of the electrodes, the length of time the modulating signal is applied, and the amplitude of the modulating signal.

Abstract: We disclose a shaping encoder configured to use a variable-length shaping code to implement fixed-input fixed-output (FIFO) probabilistic signal shaping. In various embodiments, the variable-length shaping code can be a variable-input fixed-output code, a fixed-input variable-output code, or a variable-input variable-output code. The FIFO functionality of the shaping encoder is enabled by a control circuit that operates to: (i) check an output-overflow condition for each bit-word to be encoded using the variable-length shaping code and (ii) switch the shaping encoder from using the variable-length shaping code to using a suitable FIFO code if the output-overflow condition is satisfied. Some embodiments of the shaping encoder can incorporate a conventional FEC encoder in a manner that substantially preserves the shaping gain realized by the shaping encoder.

Abstract: An optical line card includes a plurality of coherent receivers and a plurality of optical modulators. The coherent receivers are each configured to receive a corresponding channel of a received optical superchannel. The optical modulators are each configured transmit a corresponding channel of a transmitted optical superchannel. Each of a plurality of optical splitters is configured to receive a corresponding one of a plurality of unmodulated optical signals from an optical source external to the line card. Each splitter directs a first portion of light received by that splitter to a corresponding one of the coherent receivers, and a second portion of light received by that splitter to a corresponding one of said optical modulators.

Abstract: An array of optical amplifiers that recycles the unused pump power of some or all constituent amplifiers thereof, thereby beneficially improving pump-power utilization therein compared to that of conventional optical amplifiers. In an example embodiment, different amplifiers of the array can be configured to receive approximately equal pump power and be used to independently amplify different respective optical signals. In various embodiments, the unused pump power can be recycled using one or more optical couplers and/or optical paths that appropriately interconnect different amplifiers of the array. Some embodiments have one or more optical loops configured to operate as a ring laser that regenerates pump light in response to the unused pump power being coupled thereto. Some embodiments provide a spectral gain profile suitable for amplifying WDM signals in at least some of the constituent amplifiers of the array.