Abstract: An apparatus comprises a digital signal processing module configured to receive a data stream and generate a plurality of digital multiple tones, a plurality of digital-to-analog converters coupled to the digital signal processing module, a plurality of drivers coupled to respective digital-to-analog converters, an electro-optic modulator having inputs coupled to the drivers and outputs coupled to a fiber and a multi-wavelength light source coupled to the electro-optic modulator.

Abstract: The present disclosure provides a method and system for fine estimation of a local oscillator frequency offset of a received signal at a coherent receiver, by evaluating the probability mass function (PMF) of the signal phase of output symbols at different frequencies. At frequencies other than the actual frequency offset, the signal phase is uniformly distributed in [-?,?] such that the summation of a function of PMF values where the function is convex or concave between 0 and 1 can be utilized to determine an a frequency offset to be used by the coherent receiver.

Abstract: The present applies to digital wavelength converters that convert, independently of the format in which optical data may be encoded, an input waveform at a first wavelength to an output waveform at a second wavelength. When operating in an environment where an input waveform has a pilot tone associated thereto, the method and system of the present disclosure allows for the removal of the pilot tone from the input waveform, and also allows for the addition of another pilot to the output waveform.

Abstract: System and method embodiments are provided for improving reception of direct detection optical signals. In an embodiment, a method for optical transmission includes bit loading and power loading, with a digital signal processor (DSP), transmission bits of an orthogonal frequency-division multiplexing (OFDM) signal; calculating, with the DSP, a signal-signal beat interference (SSBI) component of the bit and power loaded OFDM signal by modulating each subcarrier with a symbol; and subtracting, with the DSP, the calculated SSBI component from the bit and power loaded OFDM signal.

Abstract: Optical network devices and method for optical network communications in discrete multi-tone (DMT) are provided. A serial information signal is converted to groups of bits and loaded to parallel processing branches based on bit rates of the parallel processing branches. Each branch is configured to encode the associated group of data bits on the associated tone. A first bit rate and modulation and power allocation to a first branch of the branches may be different from a second bit rate and modulation and power allocation to a second branch of the branches. To recover the incoming data, the encoded signal may be parallel-processed using branches with different demodulation formats and provide the serial data stream.

Abstract: Quasi-reduced state trellis equalization techniques achieve low-latency inter-symbol interference (ISI) equalization by selecting a subset of accumulated path metrics (APMs) for a leading symbol to propagate over a trellis to candidate states of a trailing symbol. This simplifies the computation of APMs for candidate states of the trailing symbol. Thereafter, APMs for candidate states of the trailing symbol are computed based on the subset of APMs for the leading symbol that were propagated over the trellis. Propagating fewer than all APMs for the leading symbol to the trailing symbol reduces the complexity of APM computation at the trailing symbol.

Abstract: System and method embodiments are provided for bit loading for optical Discrete Multi-Tone Transmission (DMT). In an embodiment, a method for bit loading for optical DMT transmission or reception includes receiving, at a processor, a bit data stream, wherein the bit data stream comprises a plurality of subcarriers; assigning, with the processor, a code rate to each of a plurality of forward error correction (FEC) encoders/decoders according to a mapping of a signal-to-noise-ratio (SNR) to a code rate for each of the subcarriers or subcarrier groups, wherein each FEC encoder/decoder corresponds to a respective one of the subcarriers or a respective subcarrier group; and assigning, with the processor, a modulation format to each subcarrier or each subcarrier group according to a mapping of an SNR for each subcarrier or subcarrier group to a bit number for a corresponding subcarrier or subcarrier group.

Abstract: An apparatus comprises a front end configured to receive an optical signal, and convert the optical signal into a plurality of digital signals, and a processing unit coupled to the front end and configured to determine a best-match chromatic dispersion (CD) estimate in the optical signal by optimizing a cost function based on signal peaks of the plurality of digital signals.

Abstract: System and method embodiments are provided for carrier-signal power ratio (CSPR) control in direct detection optical systems. In an embodiment, a method for CSPR control in a direct detection optical system includes receiving an electrical signal in a receiver (RX) digital signal processor (DSP), wherein the electrical signal is obtained from a corresponding optical signal via a direct detection component; estimating, a CSPR for the electrical signal; generating one of a control signal according to the CSPR; and transmitting the control signal to one of an optical filter and a laser, wherein the wavelength control signal controls causes a center wavelength (CW) of one of the optical filter and the laser to be adjusted such that an offset between the CW of the laser and the CW of the optical filter results in a desired CSPR.

Abstract: An apparatus comprising a processing unit configured to encode a data sequence in a plurality of modulation formats to produce a multi-rate data stream, wherein a first of the modulation formats provides a first transmission data rate, and wherein a second of the modulation formats provides a second transmission data rate different from the first transmission data rate, and insert a rate change signaling block into the multi-rate data stream to indicate a rate change from the first transmission data rate to the second transmission data rate, and a frontend coupled to the processing unit and configured to convert the multi-rate data stream into an optical signal, and transmit the converted optical signal towards a remote optical receiver via an optical network.

Abstract: An apparatus comprising an optical receiver configured to receive a plurality of orthogonal frequency-division-multiplexed (OFDM) symbols comprising a first OFDM symbol and a second OFDM symbol, and a processor coupled to the optical receiver and configured to generate a first decoded signal based on the first OFDM symbol, estimate a plurality of channel parameters adaptively based on the first decoded signal, generate a second decoded signal based on the second OFDM symbol, wherein the second decoded signal is generated using the plurality of channel parameters, and wherein phase recovery is performed on the first OFDM symbol using a number of pilot subcarriers prior to generating the first decoded signal.

Abstract: A method of optical communication comprising encoding four modulated symbols to generate four encoded symbols in two orthogonal polarizations and transmitting the four encoded symbols in two successive time slots. An optical communication apparatus comprising a processor configured to receive two sequences of digital symbols in a plurality of time slots, wherein the two sequences correspond to two components of two orthogonal polarizations, wherein one digital symbol per polarization is received in each of the plurality of time slots, divide each of the two sequences into a plurality of groups using a modulo operation of time, wherein each group comprises two digital symbols received in two consecutive time slots, and adaptively equalize the four digital symbols of the two consecutive time slots using a 4×4 matrix to generate four modulated symbols, wherein the 4×4 matrix comprises 16 tap-vectors.

Abstract: A method of optical communication comprising encoding four modulated symbols to generate four encoded symbols in two orthogonal polarizations and transmitting the four encoded symbols in two successive time slots. An optical communication apparatus comprising a processor configured to receive two sequences of digital symbols in a plurality of time slots, wherein the two sequences correspond to two components of two orthogonal polarizations, wherein one digital symbol per polarization is received in each of the plurality of time slots, divide each of the two sequences into a plurality of groups using a modulo operation of time, wherein each group comprises two digital symbols received in two consecutive time slots, and adaptively equalize the four digital symbols of the two consecutive time slots using a 4×4 matrix to generate four modulated symbols, wherein the 4×4 matrix comprises 16 tap-vectors.

Abstract: The present disclosure provides a method and system for fine estimation of a local oscillator frequency offset of a received signal at a coherent receiver, by evaluating the probability mass function (PMF) of the signal phase of output symbols at different frequencies. At frequencies other than the actual frequency offset, the signal phase is uniformly distributed in [??,?] such that the summation of square of PMF (PMF sum-square) values is minimized. However at the actual frequency offset, the signal phase is no longer uniformly distributed over [??,?]; in other words the signal phase will take some specific values in [??,?], therefore a peak PMF sum-square value will result. This peak PMF value provides an indication of the actual offset frequency of the received signal.

Abstract: Embodiments are provided for a novel multi-wavelength coherent receiver (MWCR) design and operation capable of detecting multiple optical wavelength channels. The embodiments include an optical receiver comprising a polarization-diversity optical hybrid module, a multiple wavelength local oscillator (MWLO) coupled to an input of the polarization-diversity optical hybrid module, a plurality of PIN diodes coupled to the polarization-diversity optical hybrid module, a plurality of analog-to-digital converters (ADCs) coupled to the PIN diodes, and a digital signal processing (DSP) module coupled to the ADCs. The polarization-diversity optical hybrid module splits an optical signal into multiple polarization components, wherein the optical signal includes multiple channels at multiple wavelengths. The MWLO locks the optical signal to the multiple wavelengths of the channels simultaneously.

Abstract: An apparatus comprising a digital signal processor (DSP) configured to code a plurality of data sub-streams using a plurality of modulation formats to generate a plurality of coded data symbols, wherein each modulation format leads to a unique bit rate for coded data symbols associated with a modulation format, transform the coded data symbols into a frequency domain by applying Fourier transform on each coded data symbol, map the frequency-transformed data symbols onto a plurality of subcarrier signals associated with a plurality of frequency tones, wherein at least two of the subcarrier signals correspond to different modulation formats, and generate an electrical signal in a time domain based on the subcarrier signals.

Abstract: A method for wavelength conversion comprising receiving an input optical signal with a first wavelength, converting the input optical signal to a plurality of input analog signals, generating a plurality of digital signals based on the input analog signals, compensating for waveform distortions by at least filtering one or more of the digital signals to generate one or more compensated digital signals, converting the compensated digital signals to output analog signals via digital-to-analog (DA) conversion, generating an output optical signal with a second wavelength different from the first wavelength based on the output analog signals, and transmitting the output optical signal.

Abstract: An apparatus comprises a digital signal processing module configured to receive a data stream and generate a plurality of digital multiple tones, a plurality of digital-to-analog converters coupled to the digital signal processing module, a plurality of drivers coupled to respective digital-to-analog converters, an electro-optic modulator having inputs coupled to the drivers and outputs coupled to a fiber and a multi-wavelength light source coupled to the electro-optic modulator.

Abstract: Embodiments are provided to improve direct detection for optical transmissions. In an embodiment, a method by a transmitter includes adjusting, using a nonlinear equalizer (NLE), a drive voltage for an optical modulator in accordance with a mapping between the drive voltage and an output of the optical modulator. The mapping is an inverse function of a nonlinear transfer function at the optical modulator between the output and to the drive voltage. The method further includes driving, using the adjusted drive voltage, the output of the optical modulator. The output is a single-side band (SSB) signal and is sufficiently linear with respect to the drive voltage for allowing direct detection at a receiver.

Abstract: Embodiments are provided to improve direct detection for optical transmissions. In an embodiment, a method by a transmitter for a direct detection system includes driving, via a drive voltage, a single-side band (SSB) signal at an optical modulator on a first optical path of the transmitter. The SSB signal is sufficiently linear with respect to the drive voltage for allowing direct detection at a receiver. The method further includes generating a DC carrier signal on a second path of the transmitter. The SSB signal is combined with the DC carrier signal at an output of the transmitter.