Abstract: A method and apparatus are provided for decoding a plurality of codewords from a received binary bitstream. A first decoding stage processes each of the codewords with a first iterative decoding algorithm based on forward error-correction information of the codewords. A second decoding stage processes selected ones of the codewords with a second iterative decoding algorithm, which is based on forward error-correction information in the selected ones of the codewords. Each codeword selected for the second decoding stage is selected in response to an exit from the decoding of that codeword without the production of a decoded codeword. The second iterative decoding algorithm is configured to enable a greater number of iterations of decoding per codeword than the first iterative decoding algorithm.

Abstract: A low-density parity-check (LDPC) decoder comprising a pre-processor, a core decoder, and a post-processor. The pre-processor is configured to transform a received log-likelihood-ratio (LLR) sequence into a form that enables the core decoder to toggle at a reduced rate during iterative decoding processing thereof. Upon stoppage of the decoding processing corresponding to the LLR sequence, the post-processor operates to apply a complementary transformation to the output of the core decoder, which recovers the corresponding codeword of the LDPC code. An example embodiment of the LDPC decoder operating in this manner may be able to beneficially reduce the power consumption therein by about 10%.

Abstract: An apparatus, comprising: circuitry configured, in response to receipt of input data, to transmit a stream of symbols of a constellation to a modulator for modulation onto a carrier wherein a frequency of occurrence of symbols in the stream is dependent upon a probability-amplitude distribution for symbols of the constellation, wherein the probability-amplitude distribution has a kurtosis less than a target value and a shape of the probability-amplitude distribution causes low-amplitude symbols to occur more frequently on average in the stream than high-amplitude symbols.

Abstract: An apparatus, comprising: circuitry configured, in response to receipt of input data, to transmit a stream of symbols of a constellation to a modulator for modulation onto a carrier wherein a frequency of occurrence of symbols in the stream is dependent upon a probability-amplitude distribution for symbols of the constellation, wherein the probability-amplitude distribution has a kurtosis less than a target value and a shape of the probability-amplitude distribution causes low-amplitude symbols to occur more frequently on average in the stream than high-amplitude symbols.

Abstract: An apparatus includes a digital signal processor to perform perturbation-based optical nonlinearity compensation of optical data signals of a communication stream. The digital signal processor includes first digital circuits to calculate multiplicative factors for corrections to the optical data signals from products of values of the optical data signals at a reduced set of times. The reduced set is a down-sampling of the sequence of consecutive symbol times of the communication stream. The digital signal processor also includes second digital circuits to calculate the multiplicative factors for corrections to the optical data signals at the consecutive symbol times by interpolating the multiplicative factors evaluated at the reduced set of times.

Abstract: The application is related to a forward error correction mechanism in an optical coherent communication system (CS) comprising a FEC encoder (FE) and a FEC decoder (FD) on the basis of a low density parity check, LDPC, code. The FEC encoder encodes blocks of client bits into codewords by adding parity bits calculated by applying a FEC code to the client bits. Besides, the FEC decoder decodes each codeword by applying thereto an iterative message-passing algorithm, each iteration of the message-passing algorithm comprising evaluating a parity-check matrix defining the FEC code. At the FEC encoder, the coding rate of the FEC code may be varied by varying the number of client/information bits per codeword and/or the number of parity bits per codeword. At the FEC decoder, the parity-check matrix is evaluated column by column at each iteration of the message-passing algorithm. The decoder may be a belief propagation decoder.

Abstract: It is disclosed an optical coherent receiver comprising a number of decoding blocks configured to implement iterations of a FEC iterative message-passing decoding algorithm. The decoding blocks are distributed into two (or more) parallel chains of cascaded decoding blocks. The receiver also comprises an intermediate circuit interposed between the two parallel chains. The optical coherent receiver is switchable between (i) a first operating mode, in which the intermediate circuit is inactive and the two parallel chains separately implement the FEC message-passing decoding algorithm on respective client channels; and (ii) a second operating mode, in which the intermediate circuit is active and the two parallel chains jointly implement the FEC message-passing decoding algorithm on a same client channel, by cooperating through the intermediate circuit.

Abstract: It is disclosed an optical coherent receiver comprising a number of decoding blocks configured to implement iterations of a FEC iterative message-passing decoding algorithm. The decoding blocks are distributed into two (or more) parallel chains of cascaded decoding blocks. The receiver also comprises an intermediate circuit interposed between the two parallel chains. The optical coherent receiver is switchable between (i) a first operating mode, in which the intermediate circuit is inactive and the two parallel chains separately implement the FEC message-passing decoding algorithm on respective client channels; and (ii) a second operating mode, in which the intermediate circuit is active and the two parallel chains jointly implement the FEC message-passing decoding algorithm on a same client channel, by cooperating through the intermediate circuit.

Abstract: Embodiments of the disclosure include a method and apparatus for detecting and removing cycle slip. A phase-modulated signal having a plurality of phase-modulated symbols is received at an optical receiver, and, for each phase-modulated symbol, a phase-error estimate of a phase error of the phase-modulated symbol is generated. The presence of a cycle slip is then detected based on the phase-error estimates, and, a phase of each of one or more of the received phase-modulated symbols is adjusted to remove the detected cycle slip without adjusting a local oscillator.

Abstract: Embodiments of the disclosure include a method and apparatus for detecting and removing cycle slip. A phase-modulated signal having a plurality of phase-modulated symbols is received at an optical receiver, and, for each phase-modulated symbol, a phase-error estimate of a phase error of the phase-modulated symbol is generated. The presence of a cycle slip is then detected based on the phase-error estimates, and, a phase of each of one or more of the received phase-modulated symbols is adjusted to remove the detected cycle slip without adjusting a local oscillator.

Abstract: An optical transmitter for a WDM (Wavelength Division Multiplexing) passive optical network (PON) and a WDM PON comprising such an optical transmitter are disclosed. An optical transmitter comprises first mirror and second mirrors at first end and second ends of a cavity; an optical amplifier positioned within the cavity upstream from the first mirror and for amplifying light polarized in a first polarization plane; an optical waveguide for transmitting light from the optical amplifier to the second mirror and vice versa; a first non-reciprocal polarization rotator upstream of the optical amplifier and downstream of the optical waveguide; and a second non-reciprocal polarization rotator upstream of the optical waveguide and downstream of the first mirror; wherein the first and second non-reciprocal polarization rotators rotate the polarization of the light such that light which re-enters the optical amplifier after having been reflected by the second mirror is polarized in the first polarization plane.