A communications system comprises a ground hub in a background area, aerial vehicles flying in a formation with slowly varying spacing between the aerial vehicles, and a user terminal in a region within a foreground area. The foreground area is spatially separate from the background area. The ground hub comprises a ground-based beam forming facility (GBBF) for receiving and transforming input signals into beam-formed signals, and a first antenna system coupled to the GBBF for transmitting concurrently the beam-formed signals in a first frequency band to respective aerial vehicles via respective background links. The aerial vehicles receive respectively the beam-formed signals via the background links and transmit respectively the beam-formed signals as respective signal beams covering at least the region within the foreground area in a second frequency band. The user terminal comprises a second antenna system for receiving concurrently the signal beams via foreground links to the aerial vehicles.

The present invention discloses an optical switching apparatus, an optical cross-connect node, and an optical signal switching method. The optical switching apparatus includes: N input ports, N OAM modulators in a one-to-one correspondence with the N input ports, an OAM splitter, and M output ports, where the M output ports are in a one-to-one correspondence with M OAM modes; a first input port of the input ports is configured to input a first optical signal, a target output port of the first optical signal is a first output port; a first OAM modulator corresponding to the first input port modulates the first optical signal into an optical signal of a first OAM mode corresponding to the first output port; the OAM splitter transmits, to the first output port, the first optical signal received from the first OAM modulator; and the first output port outputs the first optical signal.

An optical modulator has a continuous wave laser input, an RF input, a bias and dither input and an output. A photodiode connected to an output tap produces a voltage that is amplified. Noise is removed from the amplified output. A spread-spectrum dither harmonic is generated and supplied to a multiplier with the amplified and filtered feedback and is used to create a DC bias. A spread-spectrum dither is created and added to the DC bias. Spread spectrum dither and bias both are applied to the bias input of optical modulator. The bias and spread spectrum dither controller is usable with other non-optical modulators and other electronic devices.

An optical receiver comprises an optical port configured to receive an encoded optical signal, and a demodulation block indirectly coupled to the port and comprising a multiplexer, wherein the multiplexer is configured to receive an encoded electrical signal, wherein the encoded electrical signal is associated with the encoded optical signal, and wherein the encoded electrical signal is encoded using a code division multiple access (CDMA) scheme, receive a code associated with the scheme, perform a dot multiplication of the encoded electrical signal and the code, and generate a differential voltage based on the dot multiplication.

Aircrafts or unmanned air vehicles flying near Earth are used as airborne communications towers or relays. Using techniques of ground based beam forming and wavefront multiplexing enhance the ability to coherently combine the power of the communication signals, and improve the signal-to-noise ratio.

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.

An optical line terminal transmitter front-end, an optical network terminal receiver front-end and a bit-interleaved passive optical network (BIPON). In one embodiment, the transmitter front-end includes: (1) a bit interleaver configured to group and interleave a plurality of user bit-streams to yield a combined single bit-stream, (2) an encoder coupled to the bit interleaver and configured to encode multiple bits of the single bit-stream into a multi-level code corresponding to a 2.sup.m-level multi-level signal and (3) a multi-level modulator coupled to the encoder and configured to modulate the multi-level code into the 2.sup.m-level multi-level signal.

Consistent the present disclosure, a network or system is provided in which a hub or primary node may communication with a plurality of leaf or secondary nodes. The hub node may operate or have a capacity that may be greater than that of the leaf nodes. Accordingly, relatively inexpensive leaf nodes may be deployed that 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, and optical add/drop multiplexer, for example. Consistent with an aspect of the present disclosure, optical subcarriers may be transmitted over such connections. 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. In addition, the subcarriers may be employed using multiple access techniques, such as frequency division multiplexing (FDM) and time-division multiple access (TDMA), so that the primary node can communicate with a relatively large number of secondary nodes. In addition, an out-of-band control channel may be provided to carry control information from the primary node to the secondary nodes, as well as from the secondary nodes to the primary nodes.

Transmitters and receivers, including a transmitter, comprising: a laser operable to output light; a processor operable to receive data and provide a plurality of electrical signals based on the data; and a modulator operable to modulate the light to provide a plurality of optical subcarriers, spectrally adjacent optical subcarriers of the plurality of optical subcarriers being spaced from one another by a guard band, a first one of the plurality of subcarriers carrying first control information, and a second one of the plurality of subcarriers carrying second control information, the first control information being indicative of a first parameter associated with a first node remote from the transmitter and the second control information being indicative of a second parameter associated with a second node remote from the transmitter.

An optical communication system includes at least one wave division multiplex (WDM) transmitter configured to generate WDM signals in multiple channels on a light guide, and a Code Division Multiple Access (CDMA) symbol generator coupled to modulate output of the WDM transmitter at a frequency below a noise floor of the WDM signals.