A method includes mapping, by an optical transceiver, a received first OTU4 signal to a first FlexO frame without interleaving the first OTU4 signal into an ODUC signal prior to mapping the first OTU4 signal to the first FlexO frame. The method also includes communicating, by the optical transceiver, the first FlexO frame with the mapped first OTU4 signal to a coherent DSP over a first FOIC.

Optical ground terminals (OGT) allowing high optical rate communications for line of sight and non-line of sight operating conditions are disclosed. The described devices include a multifaceted structure where optical telescopes, phase array antennas, and arrays of optical detectors are disposed. Methods to calculate angle-of-arrival based the contributions from optical detectors are also disclosed.

Systems and methods include receiving a plurality of symbols that are part of a defined Digital Signal Processing (DSP) frame for coherent optical communication, wherein the DSP frame structure has a messaging channel incorporated therein that includes a subset of the plurality of symbols; capturing multiple samples of the messaging channel; and determining a message in the messaging channel based on analysis of the multiple samples. The method can further include transmitting, in the messaging channel, a reply to the message with the reply being repeated multiple times. The analysis is performed prior to Forward Error Correction (FEC) decoding on the data path.

Optical signal to noise ratios that more accurately characterize optical link noise are determined. As noise induced by an optical receiver does not generally vary with an input optical signal power, a power of an incoming optical signal is varied at the receiver. A resulting variation in noise measure represents a variation in link noise and does not include any variation caused by receiver noise, as receiver noise does not generally vary with optical signal power. Thus, the contribution of optical link noise can be discerned from other noise induced by the receiver itself. A more accurate characterization of optical link performance is thus provided.

First compensation circuitry includes a first digital filter compensating a phase difference between a phase of a symbol of a received signal and a sampling timing, and first filter coefficient calculation circuitry calculating a filter coefficient of the first digital filter as a first filter coefficient. Second filter coefficient calculation circuitry calculates, as a second filter coefficient, a filter coefficient for adaptive equalization that compensates distortion due to temporally changing polarization dispersion, based on an output of the first digital filter. Coefficient combination circuitry combines the first filter coefficient and the second filter coefficient. Second compensation circuitry includes a second digital filter which uses a filter coefficient combined by the coefficient combination circuitry and performs a compensation of the phase difference between the phase of the symbol of the received signal and the sampling timing, and a process of the adaptive equalization at the same time.

A performance monitor configured to unify at least two different signal-quality estimates into a single performance metric such that a systematic error associated with the performance metric can be approximately constant or smaller than a specified fixed limit over a significantly wider range of data-link conditions than that of a conventional performance metric of similar utility. In an example embodiment, the performance metric can be based on a weighted sum of two different SNR estimates, obtained from an error count of the receiver's FEC decoder and from a constellation scatter plot generated using the receiver's symbol decoder, respectively. Different weights for the weighted sum may be selected for different data-link conditions, e.g., using SNR thresholding, analytical formulas, or pre-computed look-up tables. The performance metric may be supplied to a control entity and considered thereby as a factor in a possible decision to trigger protective switching and/or a transponder-mode change.

Provided is a device which includes a method for the coherent detection of an optical signal, including the following steps of providing a vertically illuminable photodiode; producing an optical reference signal; radiating the optical signal and the reference signal into the photodiode in such a way that the two signals at least partially interfere with each other. Radiating the optical signal into the photodiode is effected via a first side of the photodiode, and radiating the reference signal into the photodiode is effected via a second side of the photodiode, or, vice versa, the reference signal is radiated into the photodiode via the first side of the photodiode and the optical signal is radiated into the photodiode via the second side.

A signal processing device includes: a first conversion circuit that, among optical signals of channels included in wavelength division multiplexed optical signal, converts electric field signals that indicate electric field components of the optical signal of a predetermined channel, from time domain signals into frequency domain signals; a filter that passes the electric field signals converted into the frequency domain signals with a passband; a second conversion circuit that converts the electric field signals, from the frequency domain signals into the time domain signals; an amplitude measurement circuit that measures first amplitudes of the electric field signals and second amplitudes of the electric field signals; and a notification circuit that notifies a power measurement device that measures power of the optical signal of the predetermined channel, of the first amplitudes and the second amplitudes used in correction of a measurement error of the power of the optical signal.

A signal processing device processes reception signals of optical signals received by a receiver when the optical signals transmitted from a transmitter are propagated to the receiver via a plurality of paths, and includes: a signal-to-noise ratio calculating unit that calculates signal-to-noise ratios of the optical signals that have been propagated through the respective paths, from propagation distances of the optical signals in the respective paths, intensities of the optical signals transmitted from the transmitter, and intensities of noise with respect to the optical signals transmitted from the transmitter; an amplitude adjusting unit that adjusts amplitudes of the reception signals of the optical signals that have been propagated through the respective paths, using the corresponding signal-to-noise ratios calculated by the signal-to-noise ratio calculating unit; and a signal combining unit that combines the reception signals whose amplitudes have been adjusted by the amplitude adjusting unit.

In order to reduce the amount of calculation for signal distortion compensation, this filter coefficient updating device for updating the filter coefficients of a plurality of filters in a filter layer comprising the plurality of filters, which are connected in a first plurality of stages with respect to received data, is provided with: a deriving unit for deriving the respective filter coefficients of the plurality of filters in one or a plurality of stages included in the first plurality of stages, by means of output data output from the last stage of the first plurality of stages; and an updating unit for updating each of the filter coefficients.