Abstract: An optical signal receivers, systems including the optical signal receivers, and methods of operating the same include a multimode fiber circulator including a first port, a second port, and a third port, a first multimode fiber cable coupled to the first port and having an input configured to receive a complex modulated optical signal and provide the complex modulated optical signal to the first port of the multimode fiber circulator, a second multimode fiber cable including a low Q optical resonator coupled to the second port of the multimode fiber circulator that is configured to receive the complex modulated optical signal from the second port of the multimode circulator, and a third multimode fiber cable coupled to the third port of the multimode fiber circulator that is configured to receive a reflected optical signal from the third port of the multimode circulator, the reflected optical signal being reflected from the low Q optical resonator.

Abstract: Disclosed is a microwave cavity resonator used as a phase change (phase modulation) to intensity change (intensity or amplitude modulation) converter. Certain aspects and embodiments include resonant circuits, such as a resistor, inductor and capacitor (RLC) circuit. Certain aspects and embodiments convert changes in phase to changes in output voltage to perform analog demodulation of a phase modulated microwave carrier. Certain aspects and embodiments use resonance when the reactive components of the circuit (capacitive and inductive components) are equal in magnitude and 180 degrees out of phase with one another, thereby cancelling out the reactance component of the circuit’s impedance.

Abstract: Aspects and examples are directed to programmable optical finite impulse response filters and optical infinite impulse response filters, which may be implemented as photonic integrated circuits.

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: Disclosed is a microwave cavity resonator used as a phase change (phase modulation) to intensity change (intensity or amplitude modulation) converter. Certain aspects and embodiments include resonant circuits, such as a resistor, inductor and capacitor (RLC) circuit. Certain aspects and embodiments convert changes in phase to changes in output voltage to perform analog demodulation of a phase modulated microwave carrier. Certain aspects and embodiments use resonance when the reactive components of the circuit (capacitive and inductive components) are equal in magnitude and 180 degrees out of phase with one another, thereby cancelling out the reactance component of the circuit's impedance.

Abstract: An optical signal receivers, systems including the optical signal receivers, and methods of operating the same include a multimode fiber circulator including a first port, a second port, and a third port, a first multimode fiber cable coupled to the first port and having an input configured to receive a complex modulated optical signal and provide the complex modulated optical signal to the first port of the multimode fiber circulator, a second multimode fiber cable including a low Q optical resonator coupled to the second port of the multimode fiber circulator that is configured to receive the complex modulated optical signal from the second port of the multimode circulator, and a third multimode fiber cable coupled to the third port of the multimode fiber circulator that is configured to receive a reflected optical signal from the third port of the multimode circulator, the reflected optical signal being reflected from the low Q optical resonator.

Abstract: Optical signal receivers, systems, and methods of operating the same include a non-line of sight optical signal receiver configured to receive and detect a complex modulated optical signal through a non-line of site propagation path from an optical transmitter, comprising an optical resonator configured to receive the complex modulated optical signal through the non-line of sight propagation path, and to convert the complex modulated optical signal to an intensity modulated signal, and a detector 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 to provide a detected signal.

Abstract: A system and method for recovering encoded data from a modulated baseband signal is disclosed. Aspects and embodiments of the system and method include receiving an analog input signal representing a modulated baseband signal, counting clock cycles of a reference clock, detecting a first transition and a second transition of the analog input signal indicating a first change and a second change in the modulated baseband signal, storing a first counter value corresponding to an amount of clock cycles elapsed between the first transition and the second transition, and determining a binary-valued bit sequence corresponding to the first counter value.

Abstract: Aspects and examples are directed to programmable optical finite impulse response filters and optical infinite impulse response filters, which may be implemented as photonic integrated circuits.

Abstract: An apparatus includes an antenna, a transmitter configured to generate an outgoing electrical signal, and a receiver configured to receive an incoming electrical signal. The apparatus also includes a transformer configured to couple the antenna and the transmitter such that the outgoing electrical signal causes the antenna to radiate outgoing electromagnetic energy, couple the antenna and the receiver such that the incoming electrical signal is based on incoming electromagnetic energy received by the antenna, and electrically isolate the transmitter and the receiver. The antenna may include inner and outer compensating coils, the compensating coils may be configured to additively radiate the outgoing electromagnetic energy, and the incoming electrical signal may be based on a difference between the incoming electromagnetic energy as received by the compensating coils.

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 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: Monostatic optical transceivers, systems, and methods of operating the same include a single aperture, a transmitter that provides a modulated and polarized optical transmit beam, a receiver that receives a modulated and polarized optical receive beam at an optical resonator included therein and processes the received optical receive beam to determine information from the received optical receive beam, a polarizing beam splitter that reflects the optical transmit beam, a polarization rotator that rotates the polarization of the reflected optical transmit beam by a fixed number of degrees in a transmit direction in a coordinate system of the monostatic transceiver, and a waveplate that modifies the polarization of the rotated optical transmit beam.

Abstract: A system and method for recovering encoded data from a modulated baseband signal is disclosed. Aspects and embodiments of the system and method include receiving an analog input signal representing a modulated baseband signal, counting clock cycles of a reference clock, detecting a first transition and a second transition of the analog input signal indicating a first change and a second change in the modulated baseband signal, storing a first counter value corresponding to an amount of clock cycles elapsed between the first transition and the second transition, and determining a binary-valued bit sequence corresponding to the first counter value.

Abstract: Optical signal receivers, systems, and methods of operating the same include a non-line of sight optical signal receiver configured to receive and detect a complex modulated optical signal through a non-line of site propagation path from an optical transmitter, comprising an optical resonator configured to receive the complex modulated optical signal through the non-line of sight propagation path, and to convert the complex modulated optical signal to an intensity modulated signal, and a detector 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 to provide a detected signal.

Abstract: An optical receiver includes a photonic integrator configured to accumulate optical signal energy corresponding to the input optical signal during an integration period, and to produce an output optical signal at an end of the integration period, the output optical signal having a higher intensity than the input optical signal, a shutter operable between a closed position and an open position, the shutter configured to prevent the output optical signal from exiting the photonic integrator when in the closed position and to allow the output optical signal to exit the photonic integrator when in the open position, a synchronizer coupled to the shutter and configured to control the shutter between the open position and the closed position; and a photodetector configured to receive the output optical signal when the shutter is in the open position and to produce an electrical signal corresponding to the output optical signal.

Abstract: Communications systems and methods of controlling the same include generating and processing a constant envelope phase-modulated optical signal, the systems including an optical source configured to provide a carrier waveform, an encoding module configured to encode the data as a plurality of symbol sequences, a mapping module configured to convert the plurality of symbol sequences to a plurality of phase state changes and a plurality of directions according to a path-dependent phase modulation scheme, and a phase modulator configured to modulate the carrier waveform with the plurality of phase state changes and directions to generate the constant envelope phase-modulated optical 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: Embodiments of an SLR antenna having differential signal contacts and a tuning circuit configured to tune the at least one resonance frequency of the SLR antenna to a predetermined operational frequency are disclosed. Embodiments of a tuning circuit include a balun transformer connected between the differential signal contacts of the SLR antenna and a single-ended input/output contact, a first variable capacitance connected between the balun transformer and the single-ended input/output contact, and a variable reactive component connected between the differential signal contacts of the SLR antenna and between differential contacts of the balun transformer.

Abstract: Methods and apparatus for acoustic to optical communications. In one example, a method includes performing active optical measurements of modulation-based surface deformations at a surface of a body of water using an active optical receiver to produce modulation data, the modulation-based surface deformations being representative of a modulation of a modulated acoustic signal originating beneath the surface of the body of water, between instances of performing the active optical measurements of the modulation-based surface deformations, optically measuring surface conditions of the body of water to produce channel information, and based on the modulation data and the channel information, recovering data encoded in the modulation of the modulated acoustic signal.