A wavelength-tunable optical filter control apparatus in an optical access system that uses wavelength-multiplexed optical signal of a plurality of wavelength channels includes a wavelength-tunable optical filter configured to pass an optical signal of a specific wavelength channel among the plurality of wavelength channels; a light receiving element configured to convert the optical signal that has passed through the wavelength-tunable optical filter into an electrical signal; a signal quality determining unit configured to determine a quality of the electrical signal; and a wavelength-tunable optical filter control unit configured to acquire a light intensity of the electrical signal and control a wavelength of the wavelength-tunable optical filter based on the acquired light intensity and a determination result of the quality of the electrical signal.

Aspects described herein include an optical apparatus comprising a multiple-stage arrangement of two-mode Bragg gratings comprising: at least a first Bragg grating of a first stage. The first Bragg grating is configured to transmit a first two wavelengths and to reflect a second two wavelengths of a received optical signal. The optical apparatus further comprises a second Bragg grating of a second stage. The second Bragg grating is configured to transmit one of the first two wavelengths and to reflect an other of the first two wavelengths. The optical apparatus further comprises a third Bragg grating of the second stage. The third Bragg grating is configured to transmit one of the second two wavelengths and to reflect an other of the second two wavelengths.

In a system that reduces interference between devices that transmit infrared signals, a first device transmits a first infrared signal to a second device during a first time period. The second device determines a command encoded by the first infrared signal. When the first time period has elapsed, the first device ceases transmission during a second time period. The second device transmits the second infrared signal to a third device during the second time period. As a result, transmissions from the second device to a third device are not affected by interference from transmissions by the first device. Selected signals from the first device may be permitted during the second time period, such as signals to cancel previous commands or to queue additional commands.

Exemplary arrangements relate to receivers for receiving information using very weak light pulses. The exemplary arrangements include an input optical signal having a sequence of light pulses, optical elements, and a detector. The optical elements include at least one polarisation modulator, at least one polarisation splitting cube, an element with a different optical path length for different polarisations, and at least one polarization rotating plate. Part of the optical signal follows a shorter optical path length, and part of it follows a longer optical path length. The element with different optical path lengths is placed between two polarisation beam splitter cubes. The beam splitter cubes split and then merge the sequence of pulses reducing the sequence by half and forming an amplified signal readable by the detector. Exemplary arrangements also relate to a method for transmitting information using the exemplary arrangement.

Disclosed are a method for achieving ultrahigh spectral resolution and a photonic spectral processor, which is designed to carry out the method. The disclosed photonic spectral processor overcomes the current 0.8 GHz spectral resolution limitation. The new spectral processor uses a Fabry-Perot interferometer array located before the dispersive element of the system, thus significantly improving the spectral separation resolution, which is now limited by the full width at half maximum of the Fabry-Perot interferometer rather than the spectral resolution of the dispersive element spectral as is the current situation. A proof of concept experiment utilizing two Fabry-Perot interferometers and a diffractive optical grating with spectral resolution of 6.45 GHz achieving high spectral resolution of 577 MHz is described.

An optical system for responding to distortions in incident light in a free space optical communication system includes a machine learning output storing at least an indication of multiple images and corresponding positioning or orientation attributes for one or more optical elements; a sensor configured to generate an image; and a component configured to adjust the one or more optical elements based on the generated image. Various other methods, systems, and apparatuses are also disclosed.

In high data rate receivers, comprising a photodetector (PD) and a transimpedance amplifier (TIA), a transmitted optical signal typically has poor extinction ratio, which translates into a small modulated current with a large DC current at the output of the PD. The large DC current saturates the TIA, which significantly degrades the gain and bandwidth performance. Accordingly, cancelling photo diode DC current in high data rate receivers is important for proper receiver operation. A DC current cancellation loop, comprising a low pass filter section and a trans-conductance cell (GM) are connected to the input of the TIA. PD DC current I.sub.DC is drawn from the input node of the TIA in the GM cell, such that the cancellation loop maintains the DC voltage value of the TIA input node to be the same as a reference voltage (V.sub.REF).

A directional coupler may include a first waveguide and a second waveguide. The first waveguide may include an optical input port to receive an optical signal and a first output port. The second waveguide may include a terminated port and a second output port. The first and second optical waveguides may be configured to split the optical signal such that a first portion of the optical signal is directed to the first output port and a second portion of the optical signal is directed to the second output port. The first portion of the optical signal may include first substantially equal portions of a transverse magnetic (TM) polarization mode and a transverse electric (TE) polarization mode of the optical signal. The second portion of the optical signal may include second substantially equal portions of the TM polarization mode and the TE polarization mode of the optical signal.

A demodulator can include an optical resonator. The optical resonator can include a resonant cavity that extends between a first surface that is partially reflective and a second surface that is at least partially reflective. The first surface can receive a phase-modulated optical signal that has a time-varying phase. The resonant cavity can accumulate resonant optical signal energy based at least in part on the phase-modulated optical signal. The first surface can direct a fraction of the resonant optical signal energy out of the optical resonator to form an intensity-modulated optical signal that has a time-varying intensity. A data detector can receive at least a portion of the intensity-modulated optical signal and, in response, generate an intensity-modulated electrical signal that has a time-varying intensity that corresponds to the time-varying phase of the phase-modulated optical signal.

Disclosed are optical communications systems and optical receivers including one or more optical cavity resonators. In particular, disclosed are methods and apparatus that allow for beam pointing to be maintained while permitting the receiver to tune the optical resonator to suit the wavelength, data rate and modulation format of the incoming optical signal, without requiring a coherent receiver or adaptive optics in addition to optical resonators.