Disclosed are one or more preferred geometric configurations for a device communicably coupled to a power transmission line and capable of launching transverse electromagnetic waves onto the transmission line. The waves propagate data received from a data source and may include a reflector and a coupler adjacent to each other through a transverse magnetic wave that propagates longitudinally along the surface of the transmission line.

An optical transmission apparatus outputs a main signal. An optical transmission apparatus superimposes a monitoring signal on an optical signal and outputs it. A submarine branching apparatus includes a return unit configured to return the monitoring signal received from the optical transmission apparatus and is configured to switch an output destination of the main signal received from the optical transmission apparatus to an optical transmission apparatus or the optical transmission apparatus. The optical transmission apparatus is configured to detect the monitoring signal returned from the return unit and notifies the optical transmission apparatus of a result of the detection. The optical transmission apparatus instructs the submarine branching apparatus to switch the output destination of the main signal in accordance with the notification.

The disclosure provides for a method for reacquiring a communication link between a first communication device and a second communication device. The method includes using one or more processors of the first communication device to receive historical data related to the first communication device and an environment surrounding the first communication device. The one or more processors are then used to determine one or more trends in the historical data related to fading of the communication link. Based on the one or more trends, the one or more processors are used to determine a starting time and an initial search direction for a search for the communication link. The one or more processors then execute the search at the starting time from the initial search direction.

Aspects for active alignment for assembling optical imaging systems are described herein. As an example, the aspects may include aligning an optical detector with an optical component. The optical component is configured to alter a direction of one or more light beams emitted from an image displayed by an optical engine. The aspects may further include detecting, by the optical detector, a virtual image generated by the one or more light beams emitted by the optical engine; and adjusting, by a multi-axis controller, an optical path of the one or more light beams based on one or more parameters of the virtual image collected by the optical detector.

A receiver is configured to extract a clock signal superimposed on a detection signal of light propagated to determine whether or not SNR of the detection signal is lower than SNR at which the detection signal can be demodulated; compensate a signal value of the detection signal by using a filter coefficient and output a detection signal after signal value compensation; and calculate, as the filter coefficient, a filter coefficient in which a signal value of a detection signal output from the adaptive filter is a reference value when it is determined that there is no SNR degradation, and changes the filter coefficient to a stored filter coefficient when it is determined that SNR degradation occurs.

A Field Programmable Gate Array (“FPGA”) transmitter reliability directly drives an optical modulator. Each time the FPGA is powered up, the transmitters are aligned using optical feedback for coarse and fine alignments. The fine alignment may be executed using a built-in transmitter phase interpolator Parts-Per-Million (“PPM”) controller.

Embodiments of the present invention comprise a signal processing method and apparatus for use in a satellite payload in which an input RF signal received at a receiver antenna is modulated by using a single optical carrier at the input of an optical modulator. The optical domain signal is processed and is subsequently combined with a single unmodulated optical LO tone to provide an output RF signal for radiation by a transmitter antenna or for further digital processing by an on-board processor. This results in a clean generation of the frequency-converted RF signal at the output of the opto-electrical conversion stage.

The present disclosure aims to enable communication to be performed with stable quality even when a user uses a terminal while moving. In the wireless communication system according to the present disclose, a switching control unit 15 sets switching illuminance p.sub.th for maintaining illuminance of an optical signal received by a terminal 91 at requested illuminance corresponding to throughput or higher during the time until connection switching between the communication with an optical wireless access point 92 and the communication with an RF wireless access point 93 is completed, and when the received illuminance p becomes lower than the switching illuminance p.sub.th during connection with the optical wireless access point 92, the switching control unit 15 performs connection switching from the optical wireless communication to the RF wireless communication.

An optical transmitter for quantum key distribution includes a plurality of spatially separated light sources configured to emit a light signal with the same wavelength. Each light source emits a light signal with a unique encoding. A beam combiner receives the light signals from the plurality of light sources and combines the received light signals into a combined light signal. A spatial filter is optically coupled to the beam combiner and includes an aperture that receives the combined light signal and emits a filtered light signal. The aperture has an aperture diameter less than or equal to the specified wavelength. A collimator is optically coupled to the spatial filter and receives the filtered light signal and emits a collimated light signal. An output aperture receives the collimated light signal and outputs the collimated light signal as an output light signal towards an optical receiver.

A photon entanglement system is disclosed which includes a plurality of remote nodes (Nodes A.sub.i and Node B.sub.i) each without a quantum memory; and a central entangling node (Node C) in both quantum and classical communication with the remote Nodes configured to provide photon entanglement therebetween, and includes a first and second broadband photon generators each adapted to generate sets of photon pairs at: i) random times within time-bins, and ii) random frequency bins, wherein one photon of each pair set is transmitted to an associated remote node over quantum channels, and a multiplexed Bell-state analyzer configured to receive another photon of the pair, wherein if the received photons arrive at about same time, then the received photons are marked as being entangled by the controller which communicates the associated time-bin to the associated remote nodes and thereby entangling their associated photons.