Systems and methods for identification and demodulation of complex signal formats are disclosed. In an example embodiment of the disclosed technology, a method includes identifying the signal's frame (or pattern) length, identifying the various modulation formats that compose the frame, determining the ratio of the various modulation formats in the frame, and determining the actual pattern arrangement in the frame. Further, a method can include comparing the determined arrangement to reference patterns to determine the complex signal format.

A reception apparatus includes a dispersion compensation unit configured to acquire an electrical signal resulting from conversion of an optical signal and perform, on the electrical signal, dispersion compensation with a predetermined compensation amount, a clip rate measurement unit configured to measure a clip rate for the electrical signal subjected to the dispersion compensation, and a control unit configured to detect the compensation amount that minimizes the clip rate.

A receiver for fiber optic communications.

The disclosed systems and methods for improving a launch power in an optical link. The improvement of launch power in the optical link is based on: i) selecting an optical span from one or more optical spans within the optical link; ii) applying a power dither to a plurality of the optical signals propagating in the selected optical span; iii) selecting an optical signal from the plurality of the optical signals to which the power dither is applied; iv) correlating the power dither with a performance parameter of the selected optical signal; and v) based on the correlation, adjusting the launch power of a first optical amplifier in the selected optical span to minimize the correlation to approximately equal to zero.

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.

Disclosed are a chromatic dispersion estimation method and device in optical coherent communication, wherein, the method includes: performing a fast Fourier transform on IQ-imbalance compensated data to obtain frequency-domain data in two polarization directions; calculating autocorrelation sequences of the frequency-domain data and performing an inverse fast Fourier transform on the values of the autocorrelation sequences; calculating modulus squares of the results of the inverse fast Fourier transform, and adding the results in the two polarization directions to obtain; determining a mean value of s of a plurality of data sets; calculating an index of the maximum value of, and estimating a dispersion value of the optical fiber link according to the index of the maximum value of. The abovementioned technical solution allows a significantly accurate and rapid estimation of dispersion values.

In a receiver of Quadrature Amplitude Modulation (QAM) signal, the received QAM signal is divided into multiple Quadrature Phase Shift Keying (QPSK) symbol streams. A Maximum Likelihood Symbol Estimation (MLSE) is performed on each QPSK symbol stream to recover information bits in the received QAM signal. In one advantageous aspect, complexity of implementation can be reduced by performing MLSE on QPSK signals instead of QAM signals.

The invention relates to the aspects of implementation of compensation, or equalization devices aimed at nonlinear impairment mitigation in fiber optic communication systems by means of including the spatially varying dispersive characteristics, or parameters of the underlying waveguides and their potential performance improvement from utilization of those parameters.

Disclosed herein are methods, structures, and devices that provide multi-range frequency domain compensation of chromatic dispersion within optical transmission systems that offer significant operational power savings. More specifically, a method of operating frequency domain filtering structures and circuits including FFT, frequency-domain filter multiplication and iFFT functions at a lower duty cycle for shorter overlap such that significant power savings is realized.

An optical receiver includes an equalizer to generate a plurality of equalization coefficients corresponding to a plurality of frequencies of an optical signal received by the optical receiver. The equalizer zeroes out a first subset of the equalization coefficients corresponding to a first subset of the plurality of frequency components and applies a second subset of non-zero equalization coefficients to the first signal. The optical receiver may also include a chromatic dispersion compensator to generate inverse chromatic dispersion coefficients corresponding to the plurality of frequency components, and to zero out a first subset of the inverse chromatic dispersion coefficients corresponding to the first subset of the plurality of frequency components and further to apply a second subset of non-zero inverse chromatic dispersion coefficients to a second optical signal.