Abstract: In some examples, a transmit assembly is described that may include a first optical transmitter, a second optical transmitter, and a polarizing beam combiner. The first optical transmitter may be configured to emit a first optical data signal centered at a first frequency. The second optical transmitter may be configured to emit a second optical data signal centered at a second frequency offset from the first frequency by a nominal offset n. The polarizing beam combiner may be configured to generate a dual carrier optical data signal by polarization interleaving the first optical data signal with the second optical data signal. An output of the polarizing beam combiner may be configured to be communicatively coupled via an optical transmission medium to a polarization-insensitive receive assembly.

Abstract: A method of blind tap coefficient adaptation includes receiving a digital data signal including random digital data, equalizing a first portion of the digital data signal using a first set of predetermined tap coefficients and a second portion of the digital data signal using a second set of predetermined tap coefficients. The method includes generating a first eye diagram and a second eye diagram from a first portion and a second portion of an equalized signal, respectively. The first eye diagram is compared with the second eye diagram to determine which of the sets of predetermined tap coefficients results in a data signal having a higher signal quality. The method includes inputting to an equalizer as an initial set of tap coefficients the first set of predetermined tap coefficients or the second set of predetermined tap coefficients according to the determination.

Abstract: A method of transmitting data may include receiving feedback information that includes effective channel bandwidths, signal-to-noise ratios (SNRs) associated with multiple optical channels on an optical link, and individual SNRs associated with subcarriers on each optical channel. The method may include determining multiple subcarrier power allocation schemes based on the feedback information. Each subcarrier power allocation scheme may be associated with a corresponding optical channel from the multiple optical channels and may be configured to allocate a signal power among subcarriers configured to transmit on the corresponding optical channel. The method may include determining, based on the feedback information, an optical power allocation scheme configured to allocate an optical power among the multiple optical channels. The method may include transmitting data on the multiple optical channels based on the multiple subcarrier power allocation schemes and the optical power allocation scheme.

Abstract: A method of transmitting data may include converting a stream of serial data bits into a set of parallel quadrature amplitude modulation (QAM) symbols. The method may additionally include applying a partial discrete Fourier transform-spread technique to transform a block of low-frequency subcarriers into a single-carrier QAM signal. The single-carrier QAM signal may bear information of a first subset of QAM symbols from the set of parallel QAM symbols. The method may additionally include transforming one or more remaining QAM symbols to form one or more subcarriers. Each of the one or more subcarriers may bear information of a corresponding QAM symbol from the one or more remaining QAM symbols. The method may additionally include generating a hybrid signal that includes the single-carrier QAM signal and the one or more subcarriers. The method may additionally include transmitting the hybrid signal.

Abstract: A method of blind tap coefficient adaptation includes receiving a digital data signal including random digital data, equalizing a first portion of the digital data signal using a first set of predetermined tap coefficients and a second portion of the digital data signal using a second set of predetermined tap coefficients. The method includes generating a first eye diagram and a second eye diagram from a first portion and a second portion of an equalized signal, respectively. The first eye diagram is compared with the second eye diagram to determine which of the sets of predetermined tap coefficients results in a data signal having a higher signal quality. The method includes inputting to an equalizer as an initial set of tap coefficients the first set of predetermined tap coefficients or the second set of predetermined tap coefficients according to the determination.

Abstract: In some examples, a transmit assembly is described that may include a first optical transmitter, a second optical transmitter, and a polarizing beam combiner. The first optical transmitter may be configured to emit a first optical data signal centered at a first frequency. The second optical transmitter may be configured to emit a second optical data signal centered at a second frequency offset from the first frequency by a nominal offset n. The polarizing beam combiner may be configured to generate a dual carrier optical data signal by polarization interleaving the first optical data signal with the second optical data signal. An output of the polarizing beam combiner may be configured to be communicatively coupled via an optical transmission medium to a polarization-insensitive receive assembly.

Abstract: A coherent optical transmitter circuit is disclosed in which controlled chirp is employed, enabling the suppression of nonlinear polarization scattering in dual polarization coherent systems, such as those which employ dual polarization-quadrature phase-shift keying (DP-QPSK). By separately chirping the modulated signals of each polarization tributary signal, the polarization state of the output DP-QPSK signal varies during a time period corresponding to a symbol bit period. Such controlled variations in the output DP-QPSK signal result in the mitigation of nonlinear effects associated with the network infrastructure over which the signal is transmitted, resulting in enhanced system performance. Enhanced system performance, for example, can be seen in greater reach and improved signal quality of the transmitted signal.

Abstract: An example embodiment includes optical receiver that includes a polarization beam splitter (PBS), a polarization controller, and a forward error correction (FEC). The PBS is configured to split a received optical signal having an unknown polarization state into two orthogonal polarizations (x?-polarization and y?-polarization). The polarization controller includes no more than two couplers and no more than two phase shifters per wavelength channel of the x?-polarization and the y?-polarization. The polarization controller is configured to demultiplex the x?-polarization and the y?-polarization into a first demultiplexed signal having an first polarization on which a data signal is modulated and a second demultiplexed signal having a second, orthogonal polarization on which a pilot carrier oscillator signal is encoded. The FEC decoder module is configured to correct a burst of errors resulting from resetting one of the phase shifters based on error correction code (ECC) data encoded in the data signal.

Abstract: A method of blind tap coefficient adaptation includes receiving a digital data signal including random digital data, equalizing a first portion of the digital data signal using a first set of predetermined tap coefficients and a second portion of the digital data signal using a second set of predetermined tap coefficients. The method includes generating a first eye diagram and a second eye diagram from a first portion and a second portion of an equalized signal, respectively. The first eye diagram is compared with the second eye diagram to determine which of the sets of predetermined tap coefficients results in a data signal having a higher signal quality. The method includes inputting to an equalizer as an initial set of tap coefficients the first set of predetermined tap coefficients or the second set of predetermined tap coefficients according to the determination.

Abstract: In some examples, a transmit assembly is described that may include a first optical transmitter, a second optical transmitter, and a polarizing beam combiner. The first optical transmitter may be configured to emit a first optical data signal centered at a first frequency. The second optical transmitter may be configured to emit a second optical data signal centered at a second frequency offset from the first frequency by a nominal offset n. The polarizing beam combiner may be configured to generate a dual carrier optical data signal by polarization interleaving the first optical data signal with the second optical data signal. An output of the polarizing beam combiner may be configured to be communicatively coupled via an optical transmission medium to a polarization-insensitive receive assembly.

Abstract: Consistent with the present disclosure, polarized optical signals having the same wavelength are modulated in response to ERZ drive signals, to thereby yield corresponding RZ optical signals. Each of the polarized RZ optical signals includes a plurality of RZ transitions wherein the power of the optical signal returns to zero or a minimal power between bits or symbols. The phase or timing of the ERZ drive signals, however, is controlled, so that the RZ transitions in one polarized optical signal remain interleaved with the RZ transitions of the other polarized optical signal. Alternatively, the RZ transitions of the two polarized optical signals may be controlled so that the two are temporally aligned with one another. Thus, the timing of the RZ transitions of one polarized optical signal relative to the other polarized optical signal may be adjusted to optimize system performance.

Abstract: The present invention provides a system, apparatus, and method for efficient optical amplification and transmission of a data-encoded optical signal within a networking device, such as a transmitter or receiver. In various embodiments of the invention, an optical duobinary signal or hybrid duobinary signal is generated and shaped in preparation for amplification of the optical signal by an SOA. The deleterious impact of SOA fast gain dynamics may be reduced by taking advantage of characteristics of a duobinary or hybrid duobinary signal (e.g., a relatively lower pulse amplitude and no phase encoded data) and shaping the optical duobinary pulse (e.g., smoothing amplitude swings within the signal and spectral compression).

Abstract: In some examples, a transmit assembly is described that may include a first optical transmitter, a second optical transmitter, and a polarizing beam combiner. The first optical transmitter may be configured to emit a first optical data signal centered at a first frequency. The second optical transmitter may be configured to emit a second optical data signal centered at a second frequency offset from the first frequency by a nominal offset n. The polarizing beam combiner may be configured to generate a dual carrier optical data signal by polarization interleaving the first optical data signal with the second optical data signal. An output of the polarizing beam combiner may be configured to be communicatively coupled via an optical transmission medium to a polarization-insensitive receive assembly.

Abstract: The present invention provides a system, apparatus and method to efficiently switch from one modulation format to another modulation format based upon a current route or path through a network topology of a network communication system. According to various embodiments of the invention, a network topology map is generated identifying one of a plurality of paths upon which a data stream is transmitted from a transmitter to a receiver within a network, the transmitter transmitting the data in a respective one of a plurality of data modulation formats. One or more characteristics related to one of the plurality of optical paths is measured and, based upon such measurement, a desired modulation format is selected. Upon a change in the network topology, the process is repeated such that the modulation format is continuously optimized with respect to the network topology.

Abstract: A coherent optical transmitter circuit is disclosed in which controlled chirp is employed, enabling the suppression of nonlinear polarization scattering in dual polarization coherent systems, such as those which employ dual polarization-quadrature phase-shift keying (DP-QPSK). By separately chirping the modulated signals of each polarization tributary signal, the polarization state of the output DP-QPSK signal varies during a time period corresponding to a symbol bit period. Such controlled variations in the output DP-QPSK signal result in the mitigation of nonlinear effects associated with the network infrastructure over which the signal is transmitted, resulting in enhanced system performance. Enhanced system performance, for example, can be seen in greater reach and improved signal quality of the transmitted signal.

Abstract: A variety of adaptable electronic duobinary generating filters to be used in communication systems are provided, each filter generating an adaptable electronic duobinay signal which is optimized for system impairments. According to one exemplary implementation, an adaptable electronic duobinary generating filter comprises an adaptable delay-and-add circuit, having an adaptable electronic delay element having a delay ?T: 1/T being the bit rate of the binary data input into the adaptable delay-and-add circuit, and ? being an adaptation parameter which can be optimized depending on the system impairments. In one optional implementation, the adaptable electronic delay element can be programmably adaptable to optimize against deterministic system impairments. In another optional implementation, the adaptable electronic delay element can be dynamically adaptable to optimize against dynamically varying system impairments.

Abstract: The present invention provides a system, apparatus and method to efficiently switch from one modulation format to another modulation format based upon a current route or path through a network topology of a network communication system. According to various embodiments of the invention, a network topology map is generated identifying one of a plurality of paths upon which a data stream is transmitted from a transmitter to a receiver within a network, the transmitter transmitting the data in a respective one of a plurality of data modulation formats. One or more characteristics related to one of the plurality of optical paths is measured and, based upon such measurement, a desired modulation format is selected. Upon a change in the network topology, the process is repeated such that the modulation format is continuously optimized with respect to the network topology.

Abstract: The present invention provides a system, apparatus, and method for efficient optical amplification and transmission of a data-encoded optical signal within a networking device, such as a transmitter or receiver. In various embodiments of the invention, an optical duobinary signal or hybrid duobinary signal is generated and shaped in preparation for amplification of the optical signal by an SOA. The deleterious impact of SOA fast gain dynamics may be reduced by taking advantage of characteristics of a duobinary or hybrid duobinary signal (e.g., a relatively lower pulse amplitude and no phase encoded data) and shaping the optical duobinary pulse (e.g., smoothing amplitude swings within the signal and spectral compression).

Abstract: A variety of adaptable electronic duobinary generating filters to be used in communication systems are provided, each filter generating an adaptable electronic duobinay signal which is optimized for system impairments. According to one exemplary implementation, an adaptable electronic duobinary generating filter comprises an adaptable delay-and-add circuit, having an adaptable electronic delay element having a delay ?T: 1/T being the bit rate of the binary data input into the adaptable delay-and-add circuit, and a being an adaptation parameter which can be optimized depending on the system impairments. In one optional implementation, the adaptable electronic delay element can be programmably adaptable to optimize against deterministic system impairments. In another optional implementation, the adaptable electronic delay element can be dynamically adaptable to optimize against dynamically varying system impairments.

Abstract: The present invention is directed toward a laser wavelength locking scheme suitable for incorporation into WDM systems having channel spacings of 25 GHz or less. In a preferred embodiment, light output from the laser is supplied to a filtering element, such as an in-fiber Bragg grating or an etalon, and photodetectors are used to sense light transmitted through and either reflected by the filtering element or input to the filtering element. A measured ratio corresponding to a quotient of the photocurrents generated by the photodetectors is calculated and compared to a desired ratio corresponding to a measured temperature of the filtering element when the filtering element transmits the desired wavelength to be locked. Based on the comparison of the desired and measured ratios, a temperature error value is calculated which is used to adjust the laser temperature, as well as the laser wavelength.