A receiver in a quantum key distribution (QKD) system includes a quantum optical unit configured to receive quantum signals from a transmitter of the QKD system, modulate the quantum signals based on a basis sequence, and output detection information by detecting the modulated quantum signals. The receiver further includes a signal processor configured to generate a raw key by using the detection information and the basis sequence based on a double buffering scheme.

An example apparatus includes a mode selective detector, a measurement module, a difference calculator and a threshold and alarm module. The mode selective detector detects a plurality of modes of a spatially multiplexed signal. The measurement module measures a parameter for the plurality of modes of the spatially multiplexed signal, wherein the parameter is a power or a signal to noise ratio (SNR). The difference calculator compares the measured parameter among a subset modes and/or among a known set of unperturbed parameters and determines a differential, the subset including at least one mode. The threshold and alarm module sets an alarm indicator when the differential is out of bounds.

An example apparatus includes a mode selective detector, a measurement module, a difference calculator and a threshold and alarm module. The mode selective detector detects a plurality of modes of a spatially multiplexed signal. The measurement module measures a parameter for the plurality of modes of the spatially multiplexed signal, wherein the parameter is a power or a signal to noise ratio (SNR). The difference calculator compares the measured parameter among a subset modes and/or among a known set of unperturbed parameters and determines a differential, the subset including at least one mode. The threshold and alarm module sets an alarm indicator when the differential is out of bounds.

A fiber optic assembly for supporting optical connections in a fiber optic network employing parallel optical configurations is described. In one embodiment, the fiber optic assembly includes at least two live multi-fiber components and at least one tap multi-fiber component. Optical signals are routed from one live multi-fiber component to another in a parallel optical connection configuration, with each group of optical signals corresponding to a respective group of fiber positions on each live multi-fiber component. Each group of optical signals is also routed to one of the first and second groups of fiber positions of the at least one tap multi-fiber component in a parallel optical connection configuration. In this manner, fiber optic signals can be simultaneously provided and monitored within an active fiber optic network using a parallel optical configuration without the need for interrupting network operations.

In an optical fiber monitoring system which detects physical disturbance or other parameters such as temperature or strain of a fiber where a monitor signal is transmitted along the optical fiber and analyzed to detect changes which are indicative of an event, a method is provided for periodically checking proper operation of the optical fiber monitoring system. A fiber disturbance actuator periodically causes a pattern of disturbances of a portion of the fiber at a predetermined location thereon where the disturbance is characteristic of the event to be monitored. The monitor signal is analyzed to detect the pattern of changes and in the event that expected changes are not detected, a warning is issued that the intrusion detection system is not properly operating.

In an optical fiber monitoring system which detects physical disturbance or other parameters such as temperature or strain of a fiber where a monitor signal is transmitted along the optical fiber and analyzed to detect changes which are indicative of an event, a method is provided for periodically checking proper operation of the optical fiber monitoring system. A fiber disturbance actuator periodically causes a pattern of disturbances of a portion of the fiber at a predetermined location thereon where the disturbance is characteristic of the event to be monitored. The monitor signal is analyzed to detect the pattern of changes and in the event that expected changes are not detected, a warning is issued that the intrusion detection system is not properly operating.

A fiber optic light intensity encryption method is provided. The method includes determining light intensities associated with multi-frequency light pulses emitted by a laser transmitter apparatus in response to an encryptions process. An encryption type for application of an encryption algorithm to each light intensity is determined and a first light intensity associated with a first light pulse is selected. Data indicating results of the random selection is transmitted to the laser transmitter apparatus and an initial security key is transmitted over a signaling channel of the laser transmitter apparatus. The signaling channel is secured based on the initial security key resulting in a secure signaling channel. In response, a secure bundle comprising said the secure signaling channel and an additional group of channels is generated and the data is transmitted via the secure bundle.

A reconfigurable QKD transceiver capable of transmitting and/or receiving qubits using a single optical hardware platform. This reconfigurable QKD transceiver enables various link scenarios specially for LEO-ground network, where the satellites have limited engagement time with a ground station. The reconfigurable QKD transceiver may reduce the optics SWaP by 50 percent and may allow for new mission scenarios that were otherwise not feasible with a transmitter only architecture or receiver only architecture.

A reconfigurable QKD transceiver capable of transmitting and/or receiving qubits using a single optical hardware platform. This reconfigurable QKD transceiver enables various link scenarios specially for LEO-ground network, where the satellites have limited engagement time with a ground station. The reconfigurable QKD transceiver may reduce the optics SWaP by 50 percent and may allow for new mission scenarios that were otherwise not feasible with a transmitter only architecture or receiver only architecture.

A quantum communication system, comprising: a quantum transmitter optically coupled to a first waveguide; a first communication device optically coupled to a second waveguide; a multi-core optical fiber comprising a first core and a second core; a spatial multiplexing unit, configured to optically couple the first waveguide to the first core and the second waveguide to the second core.