An heterodyne apparatus and method for measuring performance parameters of a coherent optical receiver at RF frequencies is disclosed. Two coherent lights are launched into signal and LO ports of the receiver with an optical frequency offset f. One of the lights is modulated in amplitude at a test modulation frequency F. COR performance parameters are determined by comparing two frequency components of the COR output. CMRR is determined based on a strength of a direct detection spectral line at the modulation frequency relative to that of spectrally-shifted lines at (F±f). GDV information is obtained by modulating one of the lights at two phase-locked frequencies, such as F and 2F, and comparing phases of two time-domain traces corresponding to frequency components of the COR output signal at the two frequencies.

An apparatus and method for processing a frequency offset of a pilot and a receiver where the includes: calculating a correlation function of a channel by using a receiving or received signal and a correlation length; calculating a phase to which the correlation length corresponds according to the correlation function; and calculating a corresponding slope according to phases to which at least two correlation lengths correspond when the phase to which the correlation length corresponds is greater than 2π, and estimating a frequency offset of a pilot of the channel based on the slope. Hence, estimation of a frequency offset of a pilot may be accurately achieved, thereby accurately judging channel spacing.

A method and apparatus is described for estimating a local oscillator frequency offset (LOFO) of a received optical signal in a coherent optical receiver. The method includes receiving a signal by the coherent optical receiver; digitally shifting a spectrum of the received signal according to one of a plurality of frequency shifts within a first range; equalizing each shifted signal based on a hybrid shifted filter response of a receiver driver, the hybrid shifted filter response is based on a combination of a linear shifted response and a circular shifted filter response of the receiver driver; calculating a difference of power between two sides of a spectrum of each equalized signal, the power for each side of the spectrum being calculated within a first area centered around a frequency corresponding to half of a baud rate of the received signal; determining a minimum power difference among the plurality of frequency shifts within the first range; and estimating the LOFO based on the minimum power difference.

Joint estimation of the framer index and the frequency offset in an optical communication system are described among various other features. A transmitter can transmit data frames using pilot and framer symbols. A receiver can estimate the framer index and frequency offset using the pilot and framer symbols, and identify the beginning of a header portion of a data frame. By identifying the beginning of the header portion of a data frame, the receiver can then process data received from the transmitter in a manner synchronous to the manner in which the data was transmitted by the transmitter.

An optical reception device according to an exemplary aspect of the invention includes an optical front-end means for demodulating an inputted optical signal, converting the demodulated signal into an electrical signal and outputting the electrical signal, a pre-emphasis means for adding a high frequency component to the electrical signal, a digital signal processing means for receiving input of the electrical signal with the high frequency component added thereto via a transmission wire, and for performing a digital coherent reception process on the inputted electrical signal, an error detection means for detecting a signal error in the digital coherent reception process and a feedback control means for varying the level of a high frequency component added at the pre-emphasis means and, in accordance with signal errors detected at that time, controlling the pre-emphasis means.

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.

Systems and methods for autonomous signal modulation format identification are disclosed. In an example embodiment of the disclosed technology, a method includes applying higher-order statistics to an input signal to identify the input signal's modulation format. The method may include applying higher-order statistics to the input signal to calculate higher-order cumulant values for the input signal as higher-order cumulants are indicative of a particular modulation format signature. The method may further include employing a decision tree to determine the modulation format of the input signal.

A carrier recovery unit is provided including: separation-and-output section that outputs separated symbol group formed into block; a priori state-estimation section that obtains a priori estimate acquired by estimating values processed this time from among values of intra-block frequency and central phase processed last time; provisional compensation section that provisionally compensates the phase of each separated symbol based on the a priori estimation phase; decision section that performs decision based on the reference signal for the symbol before decision, and obtains symbol after decision; error-estimation section that calculates the frequency and phase errors; a posteriori state-estimation section that obtains a posteriori estimate based on the frequency and phase errors; actual compensation section that actually compensates the phase based on the a posteriori estimation phase; and feedback processing section that feeds back the a posteriori estimate as the values processed last time to the a priori state estimation section.

An optical receiver including: a phase modulation unit that generates local oscillation light and modulates a phase of the local oscillation light; a coherent detection unit that causes a received optical signal and the local oscillation light phase-modulated by the phase modulation unit to interfere and converts the optical signal to an electrical signal; a polarization separation/adaptive equalization unit that performs polarization separation and adaptive equalization on the electrical signal after coherent detection; and decoding units that decode the polarization-separated electrical signals outputted from the polarization separation/adaptive equalization unit.

Described herein are systems and methods that allow for correcting a residual frequency offset in the GHz frequency range by using low-complexity analog circuit implementations of a broad-band frequency detector that comprises two analog polyphase filters in a dual configuration. Each filter comprises an RC network of cross-coupled capacitors that facilitate filters with opposite passbands and opposite stop-bands. In various embodiments, the outputs of the two filters are combined to obtain power metrics that when subtracted from each other, deliver a measure of the imbalance between the positive and negative halves of a frequency spectrum. Since the measure is substantially proportional to a frequency offset within a linear range spanning 5 GHz or more, the polyphase filters may be used in a broad-band frequency detector that, based on the measure, adjusts the frequency offset.