Abstract: A transmitter, receiver and transceiver system that may be used for both transmitting and receiving modulated signals are disclosed. The system includes an Electrical-to-Optical (E2O) converter that receives a Radio Frequency (RF) signal and transmits an optical signal and/or an Optical-to-Optical (O2O) that performs a wavelength translation from one wavelength to another wavelength. The Electrical-to-Optical (E2O) converter includes a vapor cell that converts the RF signal to an optical signal.

Abstract: Method and apparatus to maintain a resonant condition of an optical cavity such that the optical path length through the optical cavity is independent or minimally dependent on the angle of incidence of a received optical signal are disclosed. A material within the optical cavity has an index of refraction that varies as a function of an angle of propagation of light within the material, thereby achieving the independence of the optical path length and the angle of incidence. The resonant condition is maintained over a range of angles of incidence of the received optical signal.

Abstract: Free space optical systems and methods of controlling the same for reducing signal fading of encoded optical beams transmitted in a communication channel are provided. Adjacent pairs of a plurality of apertures are separated by a distance being at least greater than the coherence width of the propagation medium of the communication channel. Due to averaging of the beams, variation in power at an optical receiver is reduced. By using an optical resonator in the optical receiver, the beams are converted into an intensity modulation on a non-interfering basis, thereby permitting recovery and decoding of the signal.

Abstract: An optical transmitter (and methods of transmitting and receiving) includes a delay and modulation circuit configured to receive at least one optical beam and a first data signal (persistent data) and generate at least two or more modulated optical beams having the first data encoded therein. One of the modulated optical beams is a time-delayed or time-shifted version of another one of the modulated optical beams, and both beams are directed toward a target. The amount or time delay between the first and second optical beams can be modulated according to a second data signal (non-persistent data) to encode the second data therein. An optical receiver is configured to detect the two modulated optical beams and recover the first data.

Abstract: Methods and apparatus for maintaining transmitter-receiver alignment in a free space optical communications system without substantially moving the receiver element and with very little to no imparted momentum, while also allowing for higher tuning speeds and less system complexity than conventional solutions. The methods and apparatus allow for a large field of regard at the optical receiver, without the need for electromechanical gimbals to move the entire receiver unit and without the need for steering mirrors to move and align the incoming optical beam.

Abstract: An optical receiver including an optical resonator and a steering mechanism coupled to the at least one optical resonator is disclosed. The optical resonator is configured to receive a phase modulated input optical signal and to produce an intensity modulated output optical signal. An intensity modulation of the output optical signal is representative of the phase modulation of the input optical signal. The optical receiver further comprises an optical-electrical converter that detects the intensity modulated output optical signal and converts the intensity modulated output optical signal to an electrical signal, and signal processor that receives the electrical signal, performs symmetric phase change measurements based on the electrical signal, and provides a control signal to actuate the steering mechanism to steer the optical resonator to maintain normal incidence of the phase modulated input optical signal on a surface of at least one optical resonator.

Abstract: An optical transmitter and a method of producing a low-photon-density modulated optical signal are disclosed. The optical transmitter and method include an optical source configured to emit a continuous optical carrier waveform, a dilation module configured to apply a spreading code to a data payload to spread each of the plurality of symbols in time to expand the symbol duration by a dilation factor and produce a corresponding plurality of time-dilated symbols, the plurality of time-dilated symbols having a lower photon density than the plurality of symbols; a mapping module configured to map the plurality of time-dilated symbols to a modulation scheme; and a modulator configured to modulate the optical carrier waveform with the plurality of time-dilated symbols according to the modulation scheme to produce the low-photon-density modulated optical signal encoded with the plurality of time-dilated symbols corresponding to the data payload.

Abstract: An apparatus includes a phase modulator configured to modulate a phase of an incoming frequency-modulated signal based on a clock signal to generate a phase-modulated signal, where the clock signal is associated with a clock frequency. The apparatus also includes an etalon configured to receive the phase-modulated signal and generate an output signal based on the phase-modulated signal. The apparatus further includes a detector configured to identify amplitudes associated with a first harmonic of the clock frequency and a first subharmonic of the clock frequency in the output signal. In addition, the apparatus includes a decoder configured to recover information encoded in the incoming frequency-modulated signal based on instantaneous frequency deviations of the incoming frequency-modulated signal, where the instantaneous frequency deviations are identified based on relative amplitudes of the first harmonic and the first subharmonic.

Abstract: An optical signal receiver includes a multimode waveguide for receiving a complex modulated optical signal, an optical resonator that receives the complex modulated optical signal from the multimode waveguide and converts the complex modulated optical signal to an intensity modulated signal, and a detector that is configured to convert the intensity modulated signal into an electrical signal, the electrical signal having an amplitude indicative of an intensity of the intensity modulated signal from the optical resonator, and that provides a detected signal.

Abstract: An optical transmitter (and methods of transmitting and receiving) includes a delay and modulation circuit configured to receive at least one optical beam and a first data signal (persistent data) and generate at least two or more modulated optical beams having the first data encoded therein. One of the modulated optical beams is a time-delayed or time-shifted version of another one of the modulated optical beams, and both beams are directed toward a target. The amount or time delay between the first and second optical beams can be modulated according to a second data signal (non-persistent data) to encode the second data therein. An optical receiver is configured to detect the two modulated optical beams and recover the first data.

Abstract: An optical transmitter (and methods of transmitting and receiving) includes a delay and modulation circuit (or communications circuit) configured to receive at least one optical beam and a data signal and generate at least two or more modulated optical beams having the data encoded therein. One of the modulated optical beams is a time-delayed or time-shifted version of another one of the modulated optical beams, and both beams are directed toward a target.

Abstract: 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.

Abstract: An optical transmitter (and methods of transmitting and receiving) includes a delay and modulation circuit (or communications circuit) configured to receive at least one optical beam and a data signal and generate at least two or more modulated optical beams having the data encoded therein. One of the modulated optical beams is a time-delayed or time-shifted version of another one of the modulated optical beams, and both beams are directed toward a target.

Abstract: 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.

Abstract: An optical communications receiver and a process for decoding an FSK modulated optical signal are disclosed. The receiver and process are configured to receive the FSK modulated optical input signal and to produce an electrical output signal having characteristics representative of FSK modulation of the FSK modulated input signal, and to process the electrical output signal to produce a decoded information signal.

Abstract: Methods and apparatus for air to underwater communications. In one example, an optical transceiver configurable between two operational modes includes a laser assembly configured to transmit a modulated laser beam when in a first mode of the two operational modes and to transmit an unmodulated beam when in a second mode of the two operational modes, an optical receiver configured to receiver reflections of the unmodulated laser beam from a surface of a body of water and to output measurement data based on the reflections of the unmodulated laser beam, and a controller configured to determine surface conditions of the surface of the body of water based on the measurement data, to adjust at least one property of the modulated laser beam based on the surface conditions, and to operably switch the laser assembly between the first and second modes.

Abstract: An optical receiver includes an inlet aperture configured to receive an incident optical signal and a plurality of optical components configured to separate the incident optical signal into an amplitude modulated transmitted linearly s-polarized signal, an amplitude modulated transmitted linearly p-polarized signal, an amplitude modulated reflected linearly s-polarized signal, and an amplitude modulated reflected linearly p-polarized signal.

Abstract: Photo-resonator optical detectors and optical receiver systems incorporating same, In one example, an optically resonant detector includes a housing having an optical window, a photodetector disposed within the housing, and an optical resonator disposed in optical alignment with the photodetector within the housing and positioned between the optical window and the photodetector, the optical resonator being configured to receive an input optical signal via the optical window and to provide an output optical signal to the photodetector.

Abstract: An apparatus includes a tunable non-Foster matching network having (i) an amplification stage with an amplifier and (ii) a reference reactance coupled in parallel with the amplifier. The non-Foster matching network is configured to provide a negative reactance based on the reference reactance. The amplification stage also includes at least one adjustable circuit element configured to adjust a gain of the amplification stage and thereby adjust the negative reactance. In some cases, the amplification stage may include a common emitter amplification stage having a transistor, and the at least one adjustable circuit element may include an adjustable capacitor and/or multiple adjustable resistors in an emitter circuit of the transistor. In other cases, the amplification stage may include an operational amplifier and multiple resistors configured to set a gain of the operational amplifier, and the at least one adjustable circuit element may include at least one of the resistors.

Abstract: Optical signal receivers and methods are provided that include multiple optical resonators, each of which receives a portion of an arriving optical signal. Various of the optical resonators are tuned or detuned from a carrier wavelength, and produce an intensity modulated output signal in response to modulation transitions in the arriving optical signal. A detector determines phase transitions in the arriving optical signal, by analyzing the intensity modulation output signals from the optical resonators, and distinguishes between differing phase transitions that result in a common final state of the arriving optical signal.