A method and structure for equalization in coherent optical receivers. Block-based LMS (BLMS) algorithm is one of the many efficient adaptive equalization algorithms used to (i) increase convergence speed and (ii) reduce implementation complexity. Since the computation of the equalizer output and the gradient of the error are obtained using a linear convolution, BLMS can be efficiently implemented in the frequency domain with the constrained frequency-domain BLMS (FBLMS) adaptive algorithm. The present invention introduces a novel reduced complexity constrained FBLMS algorithm. This new approach replaces the two discrete Fourier transform (DFT) stages required to evaluate the DFT of the gradient error, by a simple frequency domain filtering. Implementation complexity can be drastically reduced in comparison to the standard constrained FBLMS. Furthermore, the new approach achieves better performance than that obtained with the unconstrained FBLMS in ultra-high speed coherent optical receivers.

An RF imaging receiver using photonic spatial beam processing is provided with an optical beam steerer that acts on the individual modulated optical signals to induce individual phase delays that produce a phase delay with a linear term, and possibly spherical or aspherical terms, across a two-dimensional wavefront of the composite optical signal to steer the composite optical signal and move the location of the spot on the optical detector array. The optical beam steerer may change the path length or a refractive index for each of the modulated optical signals to induce the requisite phase delays. The optical beam steerer may be implemented, for example, with a Risley prism or liquid crystal or MEMs spatial light modulator.

Upon receipt of a coherent optical signal that includes a training signal generated using a code sequence constituted by multi-value phase modulation symbols, in which a deviation angle of a vector average of a one-symbol delay differential component of a signal generated on the basis of the code sequence has a prescribed angle and a modulation phase difference between adjacent symbols has a fixed, repeated pattern, a reception training signal corresponding to a training code sequence for frequency offset estimation is detected within a reception signal acquired by converting the received coherent optical signal into an electric signal, a plurality of delay differential components are calculated on the basis of the detected reception training signal and at least two delay signals of the reception training signal, each delay signal having a different number of delay symbols, and an averaged frequency offset amount is calculated using the calculated plurality of delay differential components.

A reception apparatus includes a detection unit that detects occurrence of a phase slip in phase estimation values of time-series received symbol data, and determines an inclination of the phase slip, a delay processing unit that generates first received signal data obtained by delaying received signal data obtained from the time-series received symbol data by one symbol time interval, a phase shift unit that generates second received signal data by performing phase shift according to the inclination, only in a period in which one symbol time interval elapses, on only the received signal data of a symbol time at which the occurrence of the phase slip is detected among pieces of the received signal data, and a remainder processing unit that derives a remainder of a difference between the second received signal data and the first received signal data.

Provided is an optical transmission device including: a symbol demapping unit; a likelihood generation circuit configured to generate likelihoods relating to the reception signal; and an error correction decoding unit configured to execute soft decision decoding. The likelihood generation circuit includes: a first one-dimensional-modulation lookup table configured to input the signal of the I-axis component as an argument to output a first likelihood; a second one-dimensional-modulation lookup table configured to input the signal of the Q-axis component as an argument to output a second likelihood; and a two-dimensional-modulation lookup table configured to input, as an argument, the signal being the concatenation of the signal of the I-axis component and the signal of the Q-axis component, to generate a third likelihood. The error correction decoding unit is configured to execute the soft decision decoding based on the first likelihood, the second likelihood, and the third likelihood.

A method and structure for a coherent optical receiver device. Timing recovery (TR) is implemented after channel dispersion (i.e., chromatic dispersion (CD) and polarization mode dispersion (PMD)) compensation blocks. This architecture provides both improves performance and reduces power consumption of the device. Also, a TR loop is provided, enabling computing, by an error evaluation module, a first sampling phase error (SPE) and computing, by a timing phase information (TPI) module coupled to the error evaluation module, a second SPE from a plurality of CD equalizer taps PMD equalizer taps. The first and second SPE are combined into a total phase error (TPE) in a combining module, and the resulting TPE is filtered by a timing recovery (TR) filter coupled to an interpolated timing recovery (ITR) module and the combining module. The ITR module then synchronizes an input signal of the coherent optical receiver according to the TPE.

Consistent with the present disclosure a network is provided that includes a primary node and a plurality of secondary nodes. The primary node, as well as each of the secondary nodes, includes a laser that is “shared” between the transmit and receive sections. That is, light output from the laser is used for transmission as well as for coherent detection. In the coherent receiver, the frequency of the primary node laser is detected and, based on such detected frequency, the frequency of the secondary node laser is adjusted to detect the received information or data. Such frequency detection also serves to adjust the transmitted signal frequency, because the laser is shared between the transmit and receive portions in each secondary receiver. Light output from the primary node laser, which is also shared between transmit and receive portions in the primary node, is thus also set to a frequency that permits detection of each of the incoming optical signals by way of coherent detection. Since, in this example, only one laser is employed in the primary node, the primary node may have a simpler design and may be less expensive to manufacture compared to a primary node having multiple local oscillator lasers, each associated with a corresponding uplink optical signal.

A receiver system is provided for receiving a coherent Pulse Amplitude Modulation (PAM) encoded signal. The receiver system may include an optical polarization component configured to modulate a polarization of the received coherent PAM encoded signal. The receiver system may further include a digital signal processor (DSP) configured to perform polarization recovery between the received coherent PAM encoded signal and the LO signal using a first control loop, and to perform phase recovery between the received coherent PAM encoded signal and the LO signal using a second control loop.

A performance estimation apparatus and method for a nonlinear communication system and an electronic device. The nonlinear communication system is equated with by an equivalent model including an equivalent linear model and an equivalent additive noise model, and the equivalent additive noise outputted by the equivalent additive noise model is mathematically uncorrelated to the signal inputted into the equivalent model. Performances of the nonlinear communication system of different modulation formats at different baud rates may be accurately estimated.

A signal processing apparatus (10) according to the present disclosure includes: an overlap-type FFT processing unit (11) that performs FFT processing overlapping input subcarrier signals each other for each of FFT blocks, and a generation unit (12) that generates a signal which is obtained by frequency shifting the subcarrier signals that have been subjected to the FFT processing by the overlap-type FFT processing unit (11) by a frequency shift amount of a subcarrier, a phase offset that occurs between the FFT blocks overlapping each other being compensated in the signal.