An optical endless phase shifting device includes a Mach-Zehnder structure operated in push-pull configuration and that creates a differential phase shift. The first stage outputs combined signals which are phase shifted by a phase shift of zero or π in the second stage by phase shifters provided in both arms of the second stage or in a first arm only. These additionally phase-shifted signals are combined to at least one output signal. A control device controls the phase shifters such that endless shifting capability is provided by switching one of the phase shifters or the single phase shifter of the second stage to the respective other value when the differential phase shift reaches a given range of the differential phase shift of [0;π/2] in the configuration with two phase shifters in the second stage or [0;π/2] in the configuration with only one phase shifters in the second stage.

A low-power coherent receiver is enabled with enhanced performance for intra-datacenter reach optical interconnection applications using several techniques. The first is a coherent skew adjustment technique which enables lower-power baud-rate ADC sampling and baud-rate-spaced coherent equalization. The second is a real-valued or mixed-valued low-power coherent equalization technique, where a single-tap real-valued 4×4 MIMO equalizer plus four real-valued or two mixed-valued single-input single-out (SISO) equalizers are used for simultaneous polarization recovery, in-phase and quadrature (I/Q) phase error correction, and bandwidth equalization. The third is a power-efficient dual-DSP architecture to enhance coherent receiver performance, in which a complementary low-speed coherent DSP is introduced for optimal I/Q phase error correction and constellation decision parameters determination through more sophisticated algorithms that are too power hungry to be implemented in the primary high-speed DSP.

A method at a receiver comprises receiving a signal conveying symbols at respective positions within a clock cycle, the symbols comprising a data set consisting of data symbols and a pilot set consisting of pilot symbols; determining detected phases of the symbols based on the signal; generating first phase estimates based on the detected phases of a subset of the pilot set, and reference phases of the subset of the pilot set, the first phase estimates being associated with the positions of the pilot set; and generating second phase estimates based on the detected phases of the pilot set, reference phases of the pilot set, and the first phase estimates, the second phase estimates being associated with the positions of the pilot set and of at least a subset of the data set; and applying rotations to the detected phases of the symbols based on the second phase estimates.

When a frequency deviation compensation amount is compensated for by use of frequency shift, a phase offset occurs between adjacent input blocks included in a plurality of input blocks as divided, with the result that an error occurs in a reconstructed bit sequence. A frequency deviation compensation system of the invention is characterized by comprising: a frequency deviation compensation means for compensating for a frequency deviation occurring in a signal by use of frequency shift; and a phase offset compensation means for compensating for a phase offset occurring, in the signal, due to the frequency shift.

A system for estimating an imbalance between electrical-optical responses of an in-phase (I) channel and a quadrature (Q) channel in an optical amplitude and phase modulator (optical IQ modulator) includes an optical detector (PD), an analog-digital converter (ADC), and an imbalance operation unit that estimates an imbalance between electrical-optical responses of an I channel and a Q channel in the optical IQ modulator, wherein the imbalance operation unit includes an input signal information receiving unit that receives information regarding a first modulation signal, and an intensity information receiving unit that receives intensity information of the digitalized output signal from the ADC, and the imbalance operation unit estimates an imbalance between electrical-optical responses of an I channel and a Q channel in the optical IQ modulator using information regarding a first modulation signal and intensity information of the digitalized output signal.

Mixing between I and Q components in coherent homodyne optical signals can occur due to phase shifts, e.g. relative to the local oscillator, relative to the other signal components. In some examples, the phase shifts can arise due to thermal expansion of the optical waveguides and/or can include polarization mixing. A descrambler functions to correct for mixing between multiple signal components. The descrambler may be configured to at least partially correct for a phase difference between a first plurality of modulated optical data signals and a first local oscillator reference signal; and a controller may be configured for determining a first correction parameter for at least partially correcting for the phase difference, and for transmitting the first correction parameter to the descrambler. The controller may be configured for determining the first correction parameter from a first pilot signal transmitted with the first plurality of modulated optical data signals.

An RF imaging receiver using photonic spatial beam processing is provided with an optical beam steerer that directs the modulated optical signals to steer the composite optical signal and move the location of the spot on the optical detector array. The optical beam steerer may be implemented with one or more phase-dependent steering units in which each unit includes a waveplate and polarization grating to steer the modulated optical signals. The optical beam steerer may be configured to act 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, to steer the composite optical signal in which case the optical beam steerer may be implemented, for example, with an optical phase modulator and optical antenna in each optical channel which together form an OPA, a Risley prism or a liquid crystal or MEMs spatial light modulator.

Apparatus and method for digital signal constellation transformation are provided herein. In certain configurations, an integrated circuit includes an analog front-end that converts an analog signal vector representing an optical signal into a digital signal vector, and a digital signal processing circuit that processes the digital signal vector to recover data from the optical signal. The digital signal processing circuit generates signal data representing a signal constellation of the digital signal vector. The digital signal processing circuit includes an adaptive gain equalizer that compensates the signal data for distortion of the signal constellation arising from biasing errors of optical modulators used to transmit the optical signal.

An RF imaging receiver using photonic spatial beam processing is provided with an optical beam steerer that directs the modulated optical signals to steer the composite optical signal and move the location of the spot on the optical detector array. The optical beam steerer may be implemented with one or more phase-dependent steering units in which each unit includes a waveplate and polarization grating to steer the modulated optical signals. The optical beam steerer may be configured to act 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, to steer the composite optical signal in which case the optical beam steerer may be implemented, for example, with an optical phase modulator and optical antenna in each optical channel which together form an OPA, a Risley prism or a liquid crystal or MEMs spatial light modulator.

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.