An optical signal detection system includes: a nonlinear converter that nonlinearly converts a plurality of first optical signals into a plurality of second optical signals, and also a third optical signal into a fourth optical signal; a spectrometer that obtains each of a plurality of first spectral data items from a different one of the plurality of second optical signals, and also a third spectral data item from the fourth optical signal; and a detection device that detects the third optical signal and outputs a detection result. The detection device includes: an analyzer that performs sparse principal component analysis on the plurality of first spectral data items to generate a plurality of second spectral data items; and a detector that compares the third spectral data item with each of the plurality of second spectral data items, and detects the third optical signal based on the result of the comparison.

An optical signal detection system includes: a nonlinear converter that nonlinearly converts a plurality of first optical signals into a plurality of second optical signals, and also a third optical signal into a fourth optical signal; a spectrometer that obtains each of a plurality of first spectral data items from a different one of the plurality of second optical signals, and also a third spectral data item from the fourth optical signal; and a detection device that detects the third optical signal and outputs a detection result. The detection device includes: an analyzer that performs sparse principal component analysis on the plurality of first spectral data items to generate a plurality of second spectral data items; and a detector that compares the third spectral data item with each of the plurality of second spectral data items, and detects the third optical signal based on the result of the comparison.

A second transceiver (22) includes a guide light source (22c), a photorefractive crystal (22a), and a frequency control unit (22e). The guide light source (22c) emits guide light (Y3). A double phase conjugate mirror (22m) is formed in a crystal (22a) by scattering of reference signal light (Y1), which has a frequency different from that of the guide light and is incident on the crystal via space (15) after being transmitted from a first transceiver (21) which is a transceiver on the other side, and the guide light that is incident on the crystal in a reverse direction to that of the reference signal light. A frequency control unit (22e) couples the reference signal light emitted from the crystal (22a), which is phase-conjugate light of the guide light generated by the mirror (22m), to an optical fiber (13b).

An Optical Wireless Communication (OWC) receiver configured to receive an incoming optical beam modulated with data and output an output signal including the modulated data. A lens receives the incoming optical beam. Photodiodes positioned at a distance from the lens and proximal to the focal plane of the lens receive a fraction of the incoming optical beam and generate a photocurrent in correspondence with photons received. The photodiodes are provided in a two-dimensional array including rows and columns wherein outputs of the columns are combined and their photocurrents are summed. An amplifier connected to the combined output of the columns converts the summed photocurrents into an output signal. Interconnections of the photodiodes form at least two parallel branches wherein each branch includes a cascade of at least two photodiodes forming a combined photodetector surface.

An Optical Wireless Communication (OWC) receiver configured to receive an incoming optical beam modulated with data and output an output signal including the modulated data. A lens receives the incoming optical beam. Photodiodes positioned at a distance from the lens and proximal to the focal plane of the lens receive a fraction of the incoming optical beam and generate a photocurrent in correspondence with photons received. The photodiodes are provided in a two-dimensional array including rows and columns wherein outputs of the columns are combined and their photocurrents are summed. An amplifier connected to the combined output of the columns converts the summed photocurrents into an output signal. Interconnections of the photodiodes form at least two parallel branches wherein each branch includes a cascade of at least two photodiodes forming a combined photodetector surface.

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.

This optical communication device (1) is provided with a plurality of light-receiving elements (11) and a plurality of optical fibers (12). The plurality of optical fibers each includes a light-incident end portion (12a) for communication light and a light-emission end portion (12b) for communication light. The plurality of light-emission end portions is each arranged near each of the plurality of light-receiving elements. The plurality of light-incident end portions is each configured to be capable of being arranged in a predetermined position in a predetermined direction.

Disclosed is a method for transmitting a signal by a transmission terminal in optical wireless communication. The method may comprise: applying a phase pattern to the wavefront of an optical signal; and transmitting the optical signal. Further, the phase pattern may be determined on the basis of the optical phase conversion characteristics of a phase mask provided in the transmission terminal.

Disclosed is a method for transmitting a signal by a transmission terminal in optical wireless communication. The method may comprise: applying a phase pattern to the wavefront of an optical signal; and transmitting the optical signal. Further, the phase pattern may be determined on the basis of the optical phase conversion characteristics of a phase mask provided in the transmission terminal.

In order to improve free space optical communications, an optical communication terminal includes a laser source, a photo detecting apparatus and an optical input/output assembly. These components are controlled by a control logic. In order to have the optical communication terminal to be self-compatible, the optical input/output assembly selectively routes the outgoing beam and incoming beam depending on their respective beam polarization. To this end, the optical input/output assembly may include a polarizing beam splitter together with a quarter-wave plate.