An optical reception apparatus includes an optical coherent reception unit that generates an I-axis component of a reception signal and a Q-axis component of the reception signal based on an optical signal subjected to continuous phase frequency shift keying, a conversion unit that generates a digital signal of the I-axis component of the reception signal and a digital signal of the Q-axis component of the reception signal, a differential detection unit that generates a differential detection signal, a frequency offset compensation unit that derives a phase change amount or a temporal change in the Q-axis component of the differential detection signal whose component of a frequency offset has been compensated, a clock error detection unit that detects an amount of shift of a sampling phase of the differential detection signal whose component of the frequency offset has been compensated, based on the phase change amount or the temporal change in the Q-axis component of the differential detection signal, and a reception clock generation unit that generates the clock at a frequency adjusted such that the amount of shift becomes small.

A coherent optical receiver that is capable of obtaining separate estimates of the I/Q phase imbalances caused by the front-end circuits of the receiver and transmitter. In an example embodiment, the receiver's I/Q imbalance is estimated using equalization coefficients of a first digital equalizer located upstream from the carrier-recovery module in the train of digital-signal processing implemented at the receiver, whereas the transmitter's I/Q imbalance is estimated using equalization coefficients of a second digital equalizer located downstream from the carrier-recovery module. The receiver DSP can then use the first estimate to carry out signal processing that reduces adverse effects of the receiver's I/Q imbalance on data recovery at the receiver. The receiver can also provide the estimate of the transmitter's I/Q phase imbalance to the transmitter, which can then perform digital signal pre-distortion directed at compensating that I/Q imbalance at the transmitter.

In a method and system for decoding a differential M-ary phase or quadrature amplitude modulated signal, the incoming signal is decoded according to a plurality of different decoding rules, wherein said plurality of decoding rules correspond to different values of a resulting frequency difference or mismatch between a signal frequency and a local oscillator reference frequency. The invention allows to increase a tolerance window for the maximal allowable frequency offset, and thus helps to speed up an initial locking process or to allow for equipment which has a lower tuning granularity.

An optical receiver includes an APD that converts an input optical signal into a current signal, a TIA that converts the current signal output from the APD into a voltage signal, an LIA that shapes a waveform of the voltage signal output from the TIA, an AOC having a time constant switching function, the AOC automatically compensating for an offset voltage between differential outputs from the TIA, and a convergence-state detection circuit that outputs, after detecting convergence completion of the automatic compensation in the AOC, to the AOC, a time constant switching control signal for switching a time constant from a high-speed time constant to a low-speed time constant.

The reception (102) reception unit includes; a first processing unit processing a first signal received from a source channel, and including a filtering unit to filter said first signal in digital domain, and extract unit to extract a information from said first signal; a second processing unit processing a second signal received from a destination channel, and said source channel and said destination channel are distinct each other; a third processing unit providing said information extracted from said first signal to said second signal said third processing unit executes; providing said information from said first processing unit to said second processing unit using information lanes of a clock rate strictly lower than a symbol rate of said second signal, a monitoring unit to generate a monitor signal according to the quality of said second signal; and a control unit controlling a skew between said first signal and said second signal in a bandwidth of said filtering units in said first processing unit.

Optical network systems and components are disclosed including a transmitter comprising a digital signal processor receiving a plurality of independent data streams, the digital signal processor supplying outputs based on the plurality of independent data streams, the digital signal processor comprising a plurality of pulse shape filters corresponding to the plurality of independent data streams, the plurality of pulse shape filters configured to filter the independent data streams to produce a first subcarrier having a first frequency bandwidth and a second subcarrier having a second frequency bandwidth different than the first frequency bandwidth for the outputs.

An object is to be capable of housing an optical fiber that connects between components not to exceed a bending limit of the optical fiber in a housing of a pluggable optical module. A pluggable electric connector (11) is configured to be insertable into and removable from an optical communication apparatus (93). An optical output module (12) outputs an optical signal (LS1) and a local oscillation light (LO). An optical reception module (13) outputs a communication data signal (DAT) generated by demodulating using the local oscillation light (LO). A pluggable optical receptor (15) is configured in such a manner that optical fibers are insertable thereinto and removable therefrom. A first optical fiber (F11) is connected between the optical output module (12) and the pluggable optical receptor (15). A second optical fiber (F12) is connected between the optical output module (12) and the optical reception module (13). A third optical fiber (F13) is connected between the optical reception module (13) and the pluggable optical receptor (15). Optical fiber housing means winds extra lengths of the first to third optical fibers (F11 to F13) around a guide.

An optical communication network includes a downstream optical transceiver. The downstream optical transceiver includes at least one coherent optical transmitter configured to transmit a downstream coherent dual-band optical signal having a left-side band portion, a right-side band portion, and a central optical carrier disposed within a guard band between the left-side band portion and the right-side band portion. The network further includes an optical transport medium configured to carry the downstream coherent dual-band optical signal from the downstream optical transceiver. The network further includes at least one modem device operably coupled to the optical transport medium and configured to receive the downstream coherent dual-band optical signal from the optical transport medium. The at least one modem device includes a downstream coherent optical receiver, and a first slave laser injection locked to a frequency of the central optical carrier.

Optical network systems are disclosed, including a transmitter comprising a digital signal processor that receives data; circuitry that generate a plurality of electrical signals based on the data; a plurality of filters, each of which receiving a corresponding one of the plurality of electrical signals, a plurality of roll-off factors being associated with a respective one of the plurality of filters; a plurality of digital-to-analog converter circuits that receive outputs from the digital signal processor, the outputs being indicative of outputs from the plurality of filters; a laser that supplies light; and a modulator that receives the light and outputs from the digital-to-analog converter circuits, the modulator supplying a plurality of optical subcarriers based on the outputs of the digital-to-analog converter circuits, such that one of the plurality of optical subcarriers carrying information for clock recovery.

A coherent receiver includes a receive signal path including i) an input configured to connect a receive signal, ii) one or more signal paths connected to the input and to one or more optical hybrids, and iii) a variable optical attenuator (VOA) in each of the one or more signal paths; and a local oscillator (LO) signal path including i) an input configured to connect to an LO and the one or more optical hybrids, and ii) one or more complementary VOAs located between the input and the one or more optical hybrids, wherein the one or more complementary VOAs are configured to cancel any phase changes from the VOA in each of the one or more signal paths. The VOA in each of the one or more signal paths and the one or more complementary VOAs can be p-i-n junctions.