A directional free-space optical communication system includes a source device including a laser diode and an endpoint device including a photodiode. The endpoint device and the source device also include an adjustable optics subsystem that increases both angular and positional offset tolerance between the source device and the endpoint device.

Aspects of the disclosure provide for a method of aligning a tracking system of a communication device. The method includes receiving an optical beam at the communication device. A first beam portion is received at the tracking system, and a second beam portion is received at an optical fiber of the communication device. Using one or more processors, an first signal and an second signal is received from the tracking system. The one or more processors are also used to determine a phase difference related to the first signal and a second phase difference related to the second signal. An offset for the first signal and an offset for the second signal are determined based on the respective phase difference. The one or more processors then track the optical beam using the tracking system and the determined offsets.

It is difficult in a free space optical transmitter to transmit a beacon beam stably at low cost, and that it is impossible to maintain stable tracking; therefore, a free space optical transmitter according to an exemplary aspect of the present invention includes a laser beam transmitting means for transmitting a plurality of laser beams capable of interfering with each other and differing in one of an optical frequency and a time variation in a phase difference; and a wavefront control beam transmitting means for transmitting, to a free space, a plurality of wavefront control beams obtained by making each of the plurality of laser beams have a different wavefront.

In order to increase a compensation range for Doppler shift compensation, this digital signal processing circuit is provided with a Doppler shift compensation unit which, on the basis of a sample sequence signal which is oversampled at N (where N is an integer at least equal to 2) times a symbol rate and includes a central sample corresponding to the timing at a symbol center, and a transition sample corresponding to the timing of a symbol transition, finds a Doppler shift amount included in the sample sequence signal and performs Doppler shift compensation. The Doppler shift compensation unit includes a symbol determining unit which performs a symbol determination with respect to the central sample and a determination with respect to the transition sample. The Doppler shift compensation unit switches between these determinations for each corresponding sample and performs said determinations in order to obtain a phase difference and thereby detect the Doppler shift amount.

A position measuring apparatus instructs a first node to emit light by transmitting a first light emission pattern to the first node, instructs a second node to emit light by transmitting the first light emission pattern to the second node, when light emission following the instructed first light emission pattern is detected, and instructs the second node to emit light by transmitting a second light emission pattern that is different from the first light emission pattern, when light emission following the instructed first light emission pattern is not detected.

Traditional satellite-to-earth data transmission systems are constrained by inefficient relay schemes and/or short-duration data transfers at low data rates. Communication systems described herein achieve extremely high burst rate (e.g., 10 Gbps or greater) direct-to-Earth (DTE) data transmission over a free-space optical link between a spacecraft and a remote terminal, which may be a ground terminal or another space terminal. The optical link is established, for example, when the remote terminal is at an elevation of 20? with respect to a horizon of the remote terminal. In some embodiments, a data transmission burst contains at least 1 Terabyte of information and has a duration of 6 minutes or less. The communication system can include forward error correction by detecting a degradation of a received free-space optical signal and re-transmitting at least a portion of the free-space optical signal.

An optical receiver is provided for a diverged-beam, free space optical communications system. The optical receiver includes a demultiplexer and a detector array. The demultiplexer includes a diffractive optic configured to receive an optical beam propagating in free space. The optical beam includes a plurality of optical carrier signals of respective wavelengths for a plurality of communication channels, and the diffractive optic is configured to spatially separate the optical beam by wavelength into the plurality of optical carrier signals. The detector array includes a plurality of optical detectors configured to convert the plurality of optical carrier signals into a respective plurality of electrical signals for the plurality of communication channels. The plurality of optical detectors includes at least twice as many optical detectors as optical carrier signals in the plurality of optical carrier signals.

Aspects of the disclosure provide for a method of aligning a tracking system of a communication device. The method includes receiving an optical beam at the communication device. A first beam portion is received at the tracking system, and a second beam portion is received at an optical fiber of the communication device. Using one or more processors, an first signal and an second signal is received from the tracking system. The one or more processors are also used to determine a phase difference related to the first signal and a second phase difference related to the second signal. An offset for the first signal and an offset for the second signal are determined based on the respective phase difference. The one or more processors then track the optical beam using the tracking system and the determined offsets.

Optical communication systems and methods using coherently combined optical beams are disclosed. A representative system includes a first data source for sending first data at a first frequency of a first optical beam to a first aperture, and at a second frequency of a second optical beam to a second aperture. The system further includes a second data source for sending second data at a third frequency of a third optical beam to the first aperture, and at a fourth frequency of a fourth optical beam to the second aperture. The system also includes a first interleaver of the first aperture configured to interleave the first data at the first frequency and the second data at the third frequency; and a second interleaver of the second aperture configured to interleave the first data at the second frequency and the second data at fourth frequency.

A free space optical communication system includes an optical receiver configured to receive a light beam from an optical transmitter wirelessly in free space. The optical receiver includes an array of photodetectors and an electrical circuit. The array of photodetectors is configured to receive the light beam and convert optical signals of the light beam into electrical current. The electrical circuit is electrically coupled to the array of photodetectors and is configured to combine electrical current from the photodetectors and output a voltage or current signal.