Abstract: A method includes providing outgoing optical signals for transmission by a monostatic optical terminal using multiple transmit channels and providing incoming optical signals obtained by the monostatic optical terminal to multiple receive channels. The method also includes using a polarization beam splitter/combiner to combine the outgoing optical signals into a combined outgoing optical signal and to split a combined incoming optical signal into the incoming optical signals. The method further includes using at least one feedback loop to adjust an aim or path of at least one of the outgoing optical signals or at least one of the incoming optical signals. The method may optionally include using an optical element to convert polarizations of the combined outgoing optical signal in order to generate an output signal and to convert polarizations of an input signal in order to generate the combined incoming optical signal.

Abstract: A method includes providing outgoing optical signals for transmission by a monostatic optical terminal using multiple transmit channels and providing incoming optical signals obtained by the monostatic optical terminal to multiple receive channels. The method also includes using a polarization beam splitter/combiner to combine the outgoing optical signals into a combined outgoing optical signal and to split a combined incoming optical signal into the incoming optical signals. The method further includes using at least one feedback loop to adjust an aim or path of at least one of the outgoing optical signals or at least one of the incoming optical signals. The method may optionally include using an optical element to convert polarizations of the combined outgoing optical signal in order to generate an output signal and to convert polarizations of an input signal in order to generate the combined incoming optical signal.

Abstract: An apparatus includes polarization beamsplitters that each separate incoming and outgoing optical signals having different polarizations. The apparatus also includes directionally-dependent polarization rotation optical assemblies that each maintain a polarization of one of the incoming and outgoing optical signals and to rotate a polarization of another of the incoming and outgoing optical signals. The apparatus further includes a third polarization beamsplitter that combines the outgoing optical signals to produce transmit optical signals and separate receive optical signals to produce the incoming optical signals.

Abstract: An apparatus includes multiple dual cladding waveguides each having a single-mode interior section that transports one of multiple outgoing optical signals and a multimode section at least partially surrounding the interior section that transports one of multiple incoming optical signals. Different outgoing signals have different polarizations, and different incoming signals have different polarizations. The apparatus also includes a polarization beamsplitter that combines the multiple outgoing signals to produce transmit optical signals and separates receive optical signals to produce the multiple incoming signals.

Abstract: A system includes an optical transceiver configured to transmit and receive optical signals. The optical transceiver includes a Faraday rotator and a waveplate. The Faraday rotator and the waveplate are collectively configured to provide a relative polarization change between (i) light propagating in a first direction through the Faraday rotator and the waveplate and (ii) light propagating in a second direction opposite the first direction through the Faraday rotator and the waveplate. The waveplate may include a quarter waveplate or a half waveplate.

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 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 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: 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: 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: 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: 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 data channel system and method provide a composite signal having an overt, persistent signal channel and a non-persistent channel encoded onto a signal in the persistent channel by timing variation of the persistent channel signal.

Abstract: A system and method provide a signal carrier; an overt persistent digital channel containing a host signal and carried on the signal carrier; a non-persistent channel encoded onto the host signal by timing variation of the host signal, the non-persistent channel including access data for accessing hidden information in the host signal.

Abstract: A method for carrying data on a live host signal, comprising the steps of: varying timing in a host signal in response to data to be encoded, wherein variations in timing are smaller than a sampling period for detection and capture of the digital signal receiving the live host signal; sensing pulse timing variations in the received live host signal by comparison to a reference signal; and determining information in the sensed timing variations.

Abstract: Antennas and other transducers for use in transmitting and receiving twisted waves are disclosed. A reflector includes numerous parabolic segments having focal lengths that decrease monotonically with azimuth angle. A feed is used that is located at a focal length associated with one of the segments. Thus, each segment has a phase delay that is related to a difference between the primary focal length and the focal length of the segment. This variation of phase delay with azimuth allows twisted waves to be transmitted and received.

Abstract: A system for transmitting data using orthogonal mode division multiplexing (OMDM), a multiplexing method derived from the orbital angular momentum of photons. In one embodiment, a transmitter transmits multiple superimposed radio frequency (RF) beams each independently modulated with data, and each with a different orbital angular momentum rotational state. An OMDM receiver receives the different rotational states in separate communications channels. The OMDM states are substantially orthogonal, providing independent data channels for increased data capacity, and providing privacy.

Abstract: Imaging systems and methods for simultaneous real and Fourier plane imaging. In one example, an imaging system includes at least one optical element configured to receive and focus incident electromagnetic radiation from a viewed scene, a first detector positioned at an image plane of the at least one optical element and configured to produce a first image of the viewed scene, and a second detector positioned at a Fourier plane of the at least one optical element and configured to produce a second image of the viewed scene, the first and second detectors configured to receive the electromagnetic radiation and produce the first and second images, respectively. The system may additionally include an optical component, such as a beamsplitter, for example, configured to divide and direct the incident electromagnetic radiation to the first and second detectors.

Abstract: A system and method provide a signal carrier; an overt persistent digital channel containing a host signal and carried on the signal carrier; a non-persistent channel encoded onto the host signal by timing variation of the host signal, the non-persistent channel including access data for accessing hidden information in the host signal