A phase-lock-free system includes a control instruction unit, a low-noise high-gain optical amplifier, an optical switch, a filter, an optical delay interferometer I, an optical delay interferometer Q, a first balanced detector, a second balanced detector, an anti-coding switch unit, a parallel-serial conversion unit, and a data processing unit. The control instruction unit is connected to the optical switch, the anti-coding switch unit, and the parallel-serial conversion unit, respectively; the low-noise high-gain optical amplifier is connected to the optical switch; the optical switch is connected to the first balanced detector and the second balanced detector by means of the filter, the optical delay interferometer I, and the optical delay interferometer Q, respectively. This system improves the compatibility of a communication system at a relay node in an existing laser communication network.

A network or system in which a hub or primary node may communicate with a plurality of leaf or secondary nodes. The hub node may operate or have a capacity greater than that of the leaf nodes. Accordingly, relatively inexpensive leaf nodes may be deployed to receive data carrying optical signals from, and supply data carrying optical signals to, the hub node. One or more connections may couple each leaf node to the hub node, whereby each connection may include one or more spans or segments of optical fibers, optical amplifiers, optical splitters/combiners, and optical add/drop multiplexer, for example. Optical subcarriers may be transmitted over such connections, each carrying a data stream. The subcarriers may be generated by a combination of a laser and a modulator, such that multiple lasers and modulators are not required, and costs may be reduced. As the bandwidth or capacity requirements of the leaf nodes change, the number of subcarriers, and thus the amount of data provided to each node, may be changed accordingly. Each subcarrier within a dedicated group of subcarriers may carry OAM or control channel information to a corresponding leaf node, and such information may be used by the leaf node to configure the leaf node to have a desired bandwidth or capacity.

A network or system in which a hub or primary node may communicate with a plurality of leaf or secondary nodes. The hub node may operate or have a capacity greater than that of the leaf nodes. Accordingly, relatively inexpensive leaf nodes may be deployed to receive data carrying optical signals from, and supply data carrying optical signals to, the hub node. One or more connections may couple each leaf node to the hub node, whereby each connection may include one or more spans or segments of optical fibers, optical amplifiers, optical splitters/combiners, and optical add/drop multiplexer, for example. Optical subcarriers may be transmitted over such connections, each carrying a data stream. The subcarriers may be generated by a combination of a laser and a modulator, such that multiple lasers and modulators are not required, and costs may be reduced. As the bandwidth or capacity requirements of the leaf nodes change, the number of subcarriers, and thus the amount of data provided to each node, may be changed accordingly. Each subcarrier within a dedicated group of subcarriers may carry OAM or control channel information to a corresponding leaf node, and such information may be used by the leaf node to configure the leaf node to have a desired bandwidth or capacity.

A high data rate distribution network for low-earth orbit (LEO) satellite constellations is described. The high data rate distribution network includes multiple LEO constellations, each constellation including a number of LEO spacecraft orbiting in a LEO plane that are all connected together by by-directional free space optical links. The distribution network further includes geostationary earth orbit (GEO) spacecraft in communication with a number of ground gateways. The GEO spacecraft can receive forward communication traffic including radio-frequency (RF) and/or optical data streams uplinked from the ground gateways and can convert the received forward communication traffic into a forward aggregated traffic. The GEO spacecraft can further optically downlink the forward aggregated traffic to LEO spacecraft in a LEO constellation that is in line of sight of the GEO spacecraft. The forward aggregated traffic is then disaggregated among and received by the LEO spacecraft in the LEO constellation. Return communication traffic from each LEO spacecraft can also be aggregated into a return aggregated traffic from the LEO constellation. The return aggregated traffic is optically uplinked to a GEO spacecraft by a LEO spacecraft of the LEO constellation that is in line of sight of the GEO spacecraft. The GEO spacecraft converts the received return aggregate traffic into multiple RF and/or optical data streams that are down linked to a number of ground gateways.

An optical switching unit comprising: a plurality of arrays of multiple optical waveguides; and a switching structure controllable to direct light received from any of the optical waveguides in a first array of the plurality of arrays to one or more optical waveguides of each other array in the plurality of arrays.

Circuits and methods that implement multiplexing for photons propagating in waveguides are disclosed, in which an input photon received on a selected one of a set of input waveguides can be selectably routed to one of a set of output waveguides. The output waveguide can be selected on a rotating or cyclic basis, in a fixed order, and the input waveguide can be selected based at least in part on which one(s) of a set of input waveguides is (are) currently propagating a photon.

Apparatus for isolating transmit and receive optical beams having a common wavelength to ensure genderless interoperability in an optical communication system comprises a transmit path that propagates a transmit optical beam at a particular base wavelength and a receive path that propagates a receive optical beam at the same particular base wavelength wherein at least a portion of the receive path is separate from the transmit path. The apparatus further comprises an annular mirror having a receive beam region and a center aperture and the transmit path includes a steering mirror and the receive path also includes the steering mirror. The steering mirror has a single surface that reflects an entirety of the transmit optical beam transmitted along the transmit path and the single surface of the steering mirror reflects an entirety of the receive optical beam received along the receive path. A method of isolating transmit and receive optical beams in an optical communication system is also disclosed.

A branching unit branches a first wavelength-multiplexed optical signal input through a first transmission line, the first wavelength-multiplexed optical signal including first and second optical signals. A wavelength selection unit receives the branched first wavelength-multiplexed optical signal branched by the branching unit, receives a second wavelength-multiplexed optical signal including a third optical signal in the same band as that of the first optical signal and a fourth optical signal in the same band as that of the second optical signal through a second transmission line, outputs a third wavelength-multiplexed optical signal including the first and fourth optical signals optical to a third transmission line and output the third optical signal. A multiplexing unit outputs a fourth wavelength-multiplexed optical signal in which the branched first wavelength-multiplexed optical signal branched by the branching unit and the third optical signal output from the wavelength selection unit are multiplexed to a fourth transmission line.

A phase-lock-free system includes a control instruction unit, a low-noise high-gain optical amplifier, an optical switch, a filter, an optical delay interferometer I, an optical delay interferometer Q, a first balanced detector, a second balanced detector, an anti-coding switch unit, a parallel-serial conversion unit, and a data processing unit. The control instruction unit is connected to the optical switch, the anti-coding switch unit, and the parallel-serial conversion unit, respectively; the low-noise high-gain optical amplifier is connected to the optical switch; the optical switch is connected to the first balanced detector and the second balanced detector by means of the filter, the optical delay interferometer I, and the optical delay interferometer Q, respectively. This system improves the compatibility of a communication system at a relay node in an existing laser communication network.

An apparatus includes a first reconfigurable optical add/drop multiplexer (ROADM) to receive a first optical signal and a second ROADM to receive a second optical signal. The apparatus also includes a reconfigurable optical switch that includes a first switch, switchable between a first state and a second state, to transmit the first optical signal at the first state and block the first optical signal at the second state. The reconfigurable optical switch also includes a second switch, switchable between the first state and the second state, to transmit the second optical signal at the first state and block the second optical signal at the second state. The reconfigurable optical switch also includes an output port to transmit an output signal that is a sum of possible optical signals transmitted through the first switch and the second switch.