Aspects are generally directed to receivers and methods for actively demodulating optical signals. In one example, a receiver includes an optical resonator to receive an optical signal, the optical resonator including an active optical medium interposed between first and second semi-reflective surfaces, where the active optical medium is configured to accumulate resonant optical signal energy inside the optical resonator based on the received optical signal, the second semi-reflective surface is positioned to emit output optical signal energy, and the optical resonator is configured to disturb the output optical signal energy in response to a variation in the received optical signal. The receiver may further include a detector configured to detect the disturbance in the output optical signal energy, and a pump source coupled to the active optical medium to excite the active optical medium to generate an optical gain in the received optical signal.

Optical signal receivers and methods are provided that include an optical resonator that allows optical signal energy to enter and accumulate inside the optical resonator. A portion of optical signal energy is emitted from the optical resonator at an output, such that the emitted optical signal energy is disturbed when a transition occurs in the received optical signal energy. A detector aligned with the output detects the emitted optical signal energy and is configured to detect the disturbance to the emitted optical signal energy and determine a characteristic of the transition in the received optical signal energy based upon the disturbance.

A visible light communication (VLC) system transmits and receives visible light signals across a VLC channel that includes an air-water interface. A transmitter may be configured generates and transmits a visible light signal across the VLC channel to a remote device, and a signal modulator controls the transmitter to generate the visible light signal from a digital transmission signal in accordance with a modulation setting. A receiver processes a remote visible light signal received across the VLC channel from the remote device. A signal demodulator converts the remote visible light signal to a received digital signal.

Provided is an in-store dual-mode communication system in which shelves are disposed within a commercial space. A server is coupled to the Internet and/or a wide-area network and is configured to send and receive communications. Also provided are light-based messaging units that are located on and/or attached to such shelves, each: 1) having a light source, 2) receiving a communication from the server, and 3) in response to receipt of such communication, turning the light source on and off so as to broadcast a digital message that was included within such communication, as a binary-encoded digital signal corresponding to on/off states of the light source. A user device: (i) receives, via its light sensor, and then decodes the binary-encoded digital signal from a light-based messaging unit in order to obtain the digital message that corresponds to it; and also (ii) communicates with the server via its wireless interface.

FSO systems rely on line-of-sight, and thus can be easily impaired due to disruptions such as atmospheric turbulence. There is a need for a more robust communication system allowing longer distances to be bridged and/or downtime to be reduced. An optical transmitter is provided generating at least one optical alignment beam. The transmitter comprises at least one alignment modulator, to modulate the alignment beam with transmitter directional data. A suitable receiver may demodulate this information and use the directional data from the transmitter to simplify the attainment and/or maintenance of a sufficient degree of alignment. Additionally or alternatively, the at least one alignment beam may be used to detect, characterize and/or monitor one or more environmental parameters.

A method of detecting an optical signal, comprising the steps of: providing an avalanche photodiode (APD) comprising a multiplication region capable of amplifying an electric current, said multiplication region, in operation, having a first ionization rate for electrons and a second ionization rate for holes, wherein said first ionization rate is different in magnitude from said second ionization rate, and exposure to the optical signal causes an impulse response; exposing the APD to a modulating optical signal; providing an external circuit that induces an APD bias to the multiplication region; providing an external circuit for amplifying and processing an electric signal from the avalanche photodiode; and modulating the APD bias in a manner that is correlated with the optical signal.

A method of detecting an optical signal, comprising the steps of: providing an avalanche photodiode (APD) comprising a multiplication region capable of amplifying an electric current, said multiplication region, in operation, having a first ionization rate for electrons and a second ionization rate for holes, wherein said first ionization rate is different in magnitude from said second ionization rate, and exposure to the optical signal causes an impulse response; exposing the APD to a modulating optical signal; providing an external circuit that induces an APD bias to the multiplication region; providing an external circuit for amplifying and processing an electric signal from the avalanche photodiode; and modulating the APD bias in a manner that is correlated with the optical signal.

The present invention discloses an optical switching apparatus, an optical cross-connect node, and an optical signal switching method. The optical switching apparatus includes: N input ports, N OAM modulators in a one-to-one correspondence with the N input ports, an OAM splitter, and M output ports, where the M output ports are in a one-to-one correspondence with M OAM modes; a first input port of the input ports is configured to input a first optical signal, a target output port of the first optical signal is a first output port; a first OAM modulator corresponding to the first input port modulates the first optical signal into an optical signal of a first OAM mode corresponding to the first output port; the OAM splitter transmits, to the first output port, the first optical signal received from the first OAM modulator; and the first output port outputs the first optical signal.

Embodiments herein describe an optical receiver that demultiplexes a multi-wavelength optical signal into a plurality of optical signals with respective wavelengths. Stated differently, the various wavelengths in the received optical signal are separated into different optical signals with different wavelengths. In one embodiment, the optical receiver includes a plurality of optical filters that is aligned with a mirror to perform the demultiplexing function. The embodiments herein disclose optical receivers where the optical components performing the demultiplexing function using a ball lens aligned with optical filters.

Method and devices of controlling wavelengths in two-channel DEMUX/MUX in silicon photonics are provided. The two-channel DEMUX/MUX includes a waveguide-based delay-line-interferometer at least in receiver portion of a two-channel transceiver for DWDM optical transmission loop and is configured to split a light wave with combined two-wavelengths into one light wave with locked one channel wavelength and another light wave with locked another channel wavelength. The waveguide-based delayed-line interferometer (DLI) is characterized by a free-spectral-range configured to be equal to twice of channel spacing. The method includes tuning heater of DLI in receiver of each two-channel transceiver by using either low-frequency dither signals added on MZMs associated with respective two channels as feedback signal or one DFB laser wavelength tapped from an input of transmitter portion at one channel before or after the MZMs as a direct wavelength reference to feed into an output of receiver portion at another channel.