A method and structure for tap centering in a coherent optical receiver device. The center of gravity (CG) of the filter coefficients can be used to evaluate a proper convergence of a time-domain adaptive equalizer. However, the computation of CG in a dual-polarization optical coherent receiver is difficult when a frequency domain (FD) adaptive equalizer is adopted. In this case, the implementation of several inverse fast-Fourier transform (IFFT) stages is required to back time domain impulse response. Here, examples of the present invention estimate CG directly from the FD equalizer taps and compensate for an error of convergence based off of the estimated CG. This estimation method and associated device architecture is able to achieve an excellent tradeoff between accuracy and complexity.

An optical reception apparatus (1) of the present invention includes: a local oscillator (11) outputting local oscillation light (22); an optical mixer (12) receiving a multiplexed optical signal (21) and the local oscillation light, and selectively outputting an optical signal (23) corresponding to the wavelength of the local oscillation light from the multiplexed optical signal; a photoelectric converter (13) converting the optical signal (23) output from the optical mixer into an electric signal (24); a variable gain amplifier (15) amplifying the electric signal (24) to generate an output signal (25) whose output amplitude is amplified to a certain level; a gain control signal generating circuit (16) generating a gain control signal (26) for controlling the gain of the variable gain amplifier (15); and a monitor signal generating unit (17) generating a monitor signal (27) corresponding to the power of the optical signal (23) using the gain control signal (26).

A device for coherently detecting data in an optical signal, called a useful signal, received over a first single-mode optical fibre. The device includes: a second single-mode optical fibre that receives an oscillation optical signal; a polarization-managing device that receives as input either, in a first case, the oscillation optical signal, or, in a second case, the useful signal, and that delivers as output two separate signals, over two single-mode optical guides. The coherently detecting device is configured so that a set of the three signals, which consists of the two separate signals and of either, in the first case, the useful signal, or, in the second case, the oscillation signal, is presented to a single photodiode.

A hyperspectral radiometer may comprise one or more antennas, a electro-optical modulator modulating the received RF signal onto an optical carrier to generate a modulated signal having at least one sideband; a filter filtering the modulated signal to pass the sideband to a photodetector; and a photodetector producing an electrical signal from which information of the RF signal can be extracted. In some examples, the optical sideband may be spatially dispersed to provide a plurality of spatially separate optical components to the photodetector, where the spatially separate optical components having different frequencies and correspond to different frequencies of the received RF signal. In some examples, the passed sideband may be mixed with an optical beam having a frequency offset from the optical carrier to form a combined beam having at least one optical signal component having a beat frequency from which information of the RF signal can be extracted.

An optical receiving device that divides receive signals obtained by receiving an optical signal using a coherent detection scheme into a plurality of frequency bands, matches timing of the receive signals along a time axis between the frequency bands resulting from the division, performs a combining process of combining the receive signals contained in the plurality of frequency bands, and compensates the receive signals for waveform distortion either before or after the combining process, includes: a first wavelength dispersion compensation unit adapted to compensate the receive signals for waveform distortion in each of the frequency bands resulting from the division; a first nonlinear compensation unit adapted to compensate the receive signals belonging to each of the frequency bands and timed with each other in a time domain for a nonlinear optical effect; and a second wavelength dispersion compensation unit adapted to compensate the receive signals belonging to each of the frequency bands and compensated for the nonlinear optical effect for wavelength dispersion in each of the frequency bands.

An optical receiver includes an optical amplifier that is optically connected to a local oscillator (LO) and a plurality of optical hybrid mixers of the optical receiver and that is electrically connected to a controller. The optical amplifier is configured to receive an optical LO signal from the LO, receive a voltage value associated with an optical input signal of the optical receiver, control a power of the optical LO signal based on the voltage value, and provide, after adjusting the power of the optical LO signal, the optical LO signal to the plurality of optical hybrid mixers. The controller, is configured to determine the voltage value associated with the optical input signal and cause the voltage value to be provided to the optical amplifier.

Described herein are optical phased array receivers. In various embodiments, an optical phased array receiver includes a set of antennas, each antenna configured to receive an optical signal; a local oscillator configured to generate one or more optical carrier signals; one or more optical signal combiners coupled to the set of antennas and the local oscillator, the one or more optical signal combiners configured to combine (i) the optical signals received by the antennas and (ii) the optical carrier signal; and one or more photodetectors configured to extract information carried by one or more of the received optical signals into an electrical signal, wherein the extracted information is indicative of a phase and an amplitude of the one or more of the received optical signals.

An optical receiver includes an optical amplifier that is optically connected to a local oscillator (LO) and a plurality of optical hybrid mixers of the optical receiver and that is electrically connected to a controller. The optical amplifier is configured to receive an optical LO signal from the LO, receive a voltage value associated with an optical input signal of the optical receiver, control a power of the optical LO signal based on the voltage value, and provide, after adjusting the power of the optical LO signal, the optical LO signal to the plurality of optical hybrid mixers. The controller, is configured to determine the voltage value associated with the optical input signal and cause the voltage value to be provided to the optical amplifier.

The present disclosure generally pertains to systems and methods that utilize optical frequency discriminators based on fiber Bragg gratings. In some embodiments, an optical frequency discriminator has a polarization-maintaining fiber Bragg grating (PM-FBG), and an incoming polarized optical signal is reflected from the PM-FBG, which differentiates the two polarization modes in the incoming signal according its frequency relative to the two resonance peaks of the PM-FBG. The optical frequency discriminator then compares (e.g., subtracts) the reflected power in the two polarization modes to provide an output having an amplitude that varies linearly with the frequency of the incoming signal. This output may then be used to extract various information about the frequency of the incoming signal. As an example, the output may be used to recover data that has been frequency modulated onto the incoming signal or to characterize the frequency noise of the incoming signal.

A signal processing device includes: a memory; and a processor coupled to the memory and configured to: compensate an electric field signal representing an electric field component in an optical signal input from a transmission channel for an optical frequency offset between light sources on a transmission side and a reception side of the optical signal based on a compensation value; calculate an estimated value of the optical frequency offset from data having a fixed pattern in the electric field signal; generate a plurality of candidates for the compensation value from the estimated value; calculate power of the optical signal compensated for the optical frequency offset based on each of the plurality of candidates; and select an initial value of the compensation value from the plurality of candidates based on the power of the optical signal.