A communication network includes a coherent optics transmitter, a coherent optics receiver, an optical transport medium operably coupling the coherent optics transmitter to the coherent optics receiver, and a coherent optics interface. The coherent optics interface includes a lineside interface portion, a clientside interface portion, and a control interface portion.

A coherent transceiver includes a modulator, a receiver, a filter, a splitter, a detector, and a controller. The modulator modulates a data on the basis of laser light and outputs transmission light. The receiver receives reception light with same wavelength as the transmission light from input multiplexed light, on the basis of the laser light. The filter is arranged on an input stage of the receiver and includes a first port that inputs the multiplexed light, a filter body that transmits the reception light from the multiplexed light, and a second port that outputs the transmitted reception light. The splitter splits the transmission light travelling from the modulator and inputs the splitted transmission light. The detector detects a level of the splitted transmission light input. The controller adjusts a passband of the filter on the basis of the detected level.

An optical communication method includes: outputting light of a frequency allocated to an own device; separating the output light into mutually orthogonal polarized waves, modulating an in-phase component and a quadrature component in each of the polarized waves, and outputting an optical signal acquired by polarization synthesis of modulated component waves; acquiring information on a reception state of the optical signal in an optical reception device being a transmission destination of the optical signal; and controlling, based on the information on the reception state, a frequency of the light to be output, and adjusting a frequency offset being a difference between the frequency of the light to be output and a frequency of local oscillation light for use in coherent detection of the optical signal by the optical reception device.

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.

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).

Atmospheric turbulence degrades decoding and data recovery from optically transmitted signals. For example, atmospheric turbulence can induce power coupling from the transmitted Gaussian mode to higher-order modes, resulting in significantly degraded mixing efficiency and system performance. Systems and methods are provided to generate a signal that is a conjugate of the atmospheric noise which is combined with a received data signal to ameliorate atmospheric noise. An optical pilot beam may be transmitted with an optical data beam and received by a receiver which utilizes the optical pilot beam to generate the signal that is a conjugate of the atmospheric noise.

Apparatus, systems, and methods include leveraging the angular dependence of the angle of arrival of the incoming optical signal at an optical resonator and the output response signal to adjust the operating condition of the optical resonator. The optical resonator is dynamically tuned by rotating the optical resonator to optimize signal-to-noise ratio or other parameters for different modulation formats of the incoming optical signal or other different operating conditions.

A method for all-optical reduction of inter-channel crosstalk for spectrally overlapped optical signals for maximizing utilization of an available spectrum includes receiving a plurality of spectrally overlapped optical signals modulated with data. The method further includes generating conjugate copies of each of the plurality of optical signals using non-linear optics. The method further includes selecting the conjugate copies and adjusting an amplitude, a phase, and a delay of the conjugate copies. The method further includes performing inter-channel interference (ICI) compensation on the spectrally overlapped optical signals in an optical domain by adding the adjusted conjugate copies to the spectrally overlapped optical signals.

A mode demultiplexing hybrid (MDH) that integrates mode demultiplexing, local oscillator power splitting, and optical 90-degree hybrid using multi-plane light conversion (MPLC). Reflective cavity and transmissive systems are disclosed. The MDH may fine advantageous application as the optical front end for a coherent receiver in a space-division multiplexing (SDM) system.

A PDM-capable coherent optical receiver can be implemented using four high-bandwidth photodiodes connected in a single-ended electrical configuration. The SSBI present in the electrical output of the single-ended photodiodes is effectively canceled in the receiver DSP based on measurements of average optical power of the optical data and local-oscillator signals. In various embodiments, such measurements can be performed using relatively inexpensive circuits/components incorporated into the optical front end of the receiver. For a given signaling interval, the DSP runs an iterative algorithm to compute estimates of the in-phase and quadrature components of the optical data signal and achieve a level of performance comparable to that of a coherent optical receiver having a greater number of high-bandwidth photodiodes connected to form balanced photodetectors. The achieved reduction in the number of high-bandwidth photodiodes can advantageously be used, e.g., to significantly reduce the total cost of a high-speed optical transponder.