A system and method for radio frequency (RF) signal processing via photonic local oscillator (LO) phase control generates a set of N optical carriers and M sets of control inputs, each control input including an amplitude and/or phase control for the n.sup.th carrier. Each n.sup.th optical carrier is split into an RF path and M LO paths, the RF path including N electro-optical (EO) modulators for amplitude/phase modulation of each n.sup.th carrier per a set of N RF input signals and each m.sup.th LO path including a set of N EO modulators for amplitude/phase modulation of each n.sup.th carrier per the m.sup.th control input. Demodulators generate M in-phase and quadrature (I/Q) balanced optical outputs based on the multiplexed N combined RF optical outputs and each m.sup.th set of N combined LO optical outputs. The M I/Q balanced optical outputs are converted to the electrical and then to the digital domain.

Aspects of the present disclosure are directed to improved systems, methods, and structures providing coherent detection of DAS. In sharp contrast to the prior art, systems, methods, and structures according to aspects of the present disclosure advantageously reduce the beating diversity terms such that required memory and bandwidth are reduced over the art.

A digital communication method over an optical channel. Bob modulates a coherent optical signal with a random envelope phase φr, known to him and not to Alice, and transmits the modulated coherent optical signal (envelope) over the optical channel to Alice. Alice further modulates the envelope with a key phase φk, based on a secret key and a selected modulation scheme, to create a cipher envelope, and sends the cipher envelope towards Bob along the optical channel. Bob then demodulates a received version of the cipher envelope by removing the random envelope phase φr (known to Bob) and then measures the phase of the resulting demodulated coherent optical signal with the coherent detector to extract, to within a certain margin of error, the key phase φk, from which Alice's secret key can be decoded. Bob then uses the secret key for encrypting messages sent to Alice over any digital network.

A frame synchronization apparatus (10) according to this invention includes a multiplication unit (11) configured to multiply a received signal by an inverse complex number of a predetermined synchronization pattern with respect to a predetermined signal point on a complex space diagram for each of a plurality of symbols of the received signal, an addition average unit (12) configured to perform addition averaging of outputs from the multiplication unit for the plurality of symbols of the received signal, and a synchronization determination unit (13) configured to perform coincidence determination of whether an output from the addition average unit (12) falls within a predetermined coincidence determination range of the predetermined signal point, and determine a synchronization state of the frame synchronization based on a result of the coincidence determination. According to this invention, it is possible to provide a frame synchronization apparatus that correctly determines a synchronization state even if an error rate of received symbols is high.

An optical access network includes an optical hub having at least one processor, and a plurality of optical fiber strands. Each optical fiber strand has a first strand end connected to the optical hub. The network further includes a plurality of nodes connected to at least one segment of a first fiber strand of the plurality of optical fiber strands. Each node is sequentially disposed at respective locations along the first fiber strand at different differences from the optical hub, respectively. The network further includes a plurality of end-points. Each end-point includes a receiver. Each respective receiver (i) has a different optical signal-to-noise ratio (OSNR) from the other receivers, (ii) is operably coupled with at least one node of the plurality of nodes, and (iii) is configured to receive the same optical wavelength signal from the first fiber strand as received by the other receivers.

An objective of the present invention is to provide an optical communication system and an optical communication method that can reduce even a delay generated in processing of obtaining a transfer function for correcting distortion in digital coherent transmission. In the optical communication system according to the present invention, pilot data for estimating a transfer function for a transmission channel is transmitted through a transmission channel with a short transmission delay time, a transfer function of the transmission channel is estimated before receiving transmission data, and the transfer function is applied to other transmission channels.

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.

To provide a technology in which a differential phase modulation manner can be applied to a space environment for satellite mounting, the optical receiver 10 includes a digital signal processing unit has: a level fluctuation frequency suppression unit 320 which suppresses a level fluctuation frequency component of the peak signal; an optical delay interference control unit 330 which generates an optical delay interference control signal, which is overdrive-amplified, on the basis of the peak signal of which the level fluctuation frequency component is suppressed and applies the generated optical delay interference control signal to the optical delay interferometer 210; and a data recovery unit 310 which recovers output data on the basis of the main signal from the wideband balanced optical detector 240.

An optical source comprising: a phase-randomised light source, the phase randomised light source further comprising:

a master light source configured to intermittently generate master light pulses, wherein the phase of each generated master light pulse has a random relationship with the phase of each subsequently generated master light pulse, and wherein a first control signal is applicable to the master light source such that the master light source intermittently generates master light pulses, wherein the first control signal comprises a first and a second modulation feature in the period of time that one master light pulse is generated, wherein each phase modulation feature comprises a perturbation in the control signal applied to the master light source;
a slave light source, wherein the slave light source is optically coupled to the master light source and is configured to receive master light pulses, and wherein a second control signal is applicable to the slave light source to cause the slave light source to generate a sequence of slave light pulses during each period of time that a master light pulse is received, such that the phase of a light pulse from a sequence has a random relationship to the phase of a light pulse from a subsequent sequence, and
wherein each sequence comprises a first and a second slave light pulse that are temporally separated by a first time interval and wherein the phase difference between the first slave light pulse and the second slave light pulse depends on the phase modulation features; and
an interference apparatus, wherein the interference apparatus is optically coupled to the slave light source and is configured to receive sequences of slave light pulses, and wherein the interference apparatus comprises an interference component and a delay element, the delay element being configured to delay the received sequences of slave light pulses by the first time interval to form delayed sequences of slave light pulses, and wherein the interference apparatus is further configured to:
interfere the received sequences of slave light pulses with the delayed sequences of slave light pulses at the interference component, such that pulses from a received sequence interfere with adjacent pulses of the delayed sequence; and
output interfered pulses, wherein the interfered pulses comprise a first and a second output pulse that have a first and second predetermined amplitude respectively and a predetermined relative phase between them.

To make it possible to perform functional setting for an optical receiver from an optical transmitter using a simple configuration, an optical transmitter is provided with: a first transmit circuit which generates a first optical signal including a main signal; a second transmit circuit which generates a second optical signal including a control signal; and a first combiner which generates a channel signal in which the second optical signal is wavelength-multiplexed at one end of a wavelength band of the first optical signal.