Apparatuses and methods for far-end monitoring of transmitter IQ skew in a DSCM system are described. Soft symbols for a given subchannel and a corresponding mirror subchannel are used as joint inputs to a MIMO equalizer. The hard decision symbols for the given subchannel and mirror subchannel are used as references to compute the equalizer coefficients. An estimated phase or estimated transmitter IQ skew is computed for at least the given subchannel using the equalizer coefficients. The computation is repeated to obtain estimated phase or estimated transmitter skew for all subchannels. The transmitter IQ skew is computed using the estimates from all subchannels. The computation is performed for each polarization. The computed transmitter IQ skew is communicated back to the transmitter via optical path (for correcting the skew).

Processing a received optical signal in an optical communication network includes equalizing a received optical signal to provide an equalized signal, demodulating the equalized signal according to an m-ary modulation format to provide a demodulated signal, decoding the demodulated signal according to an inner code to provide an inner-decoded signal, and decoding the inner-decoded signal according to an outer code. Other aspects include other features such as equalizing an optical channel including storing channel characteristics for the optical channel associated with a client, loading the stored channel characteristics during a waiting period between bursts on the channel, and equalizing a received burst from the client using the loaded channel characteristics.

An optical device includes an optical coupler that inputs an optical signal received from a light source, a semiconductor optical amplifier that amplifies the optical signal received from the optical coupler, and a light receiving element that receives spontaneous emission light received from the semiconductor optical amplifier. The optical coupler includes a first input port to which the optical signal received from the light source is input, a second input port that is connected to an input stage of the light receiving element and that is different from the first input, and an output port that is connected to an input stage of the semiconductor optical amplifier, and that outputs optical signal received from the first input port to the semiconductor optical amplifier. The light receiving element receives, via the output port and the second input port, spontaneous emission light received from the semiconductor optical amplifier.

The present invention discloses a capacity optimization method for a mobile optical wireless communication system and a communication method and system. The capacity optimization method includes the following steps: establishing a mobile channel impulse response model; calculating an electrical signal-to-noise ratio (SNR) of an output of a receiver; calculating bit error rate (BER) values of an optical wireless communication system in different candidate modulation formats according to the electrical SNR of the output of the receiver; selecting a first modulation format and a second modulation format from the different candidate modulation formats; determining quantities of chips in the first modulation format and the second modulation format in each data frame; and building a time domain hybrid modulation frame according to the quantities of chips in the first modulation format and the second modulation format, modulating data by using the time domain hybrid modulation frame, and performing data transmission.

An invisible light communication system can communicate using infrared or ultraviolet light signals to provide more secure communications. The system includes a software definable and hardware configurable transmitter that uses an input, an encoder, an invisible light source, and an optic to transmit an invisible light signal. The system also includes a software definable and hardware configurable receiver that receives the invisible light signal using an optic, a detector, a detector, and an output. Applications for the invisible light communication system include fixed, deployable, vehicle, and wearable configurations for voice, video and data transmission and receipt in support of a variety of use cases: remote sensing; data exfiltration; remote control, ordnance detonation; tactical chat/messaging; point-to-point and point-to-multipoint audio communications; and full motion video.

In a distribution matching circuit, output data of a plurality of LUTs forming a hierarchical tree structure sequentially designates a combination of signal point groups in a signal space managed by an LUT in an immediately lower level, and signal point information after distribution matching is output for each LUT in the lowermost level.

Processing a received optical signal in an optical communication network includes equalizing a received optical signal to provide an equalized signal, demodulating the equalized signal according to an m-ary modulation format to provide a demodulated signal, decoding the demodulated signal according to an inner code to provide an inner-decoded signal, and decoding the inner-decoded signal according to an outer code. Other aspects include other features such as equalizing an optical channel including storing channel characteristics for the optical channel associated with a client, loading the stored channel characteristics during a waiting period between bursts on the channel, and equalizing a received burst from the client using the loaded channel characteristics.

An optical transmission device includes: a first receiver circuit, a second receiver circuit, a switch circuit, a terminator circuit, a packet buffer, a clock generator, and a signal generator. The first receiver circuit converts an optical signal received via a first route into a first electric signal. The second receiver circuit converts an optical signal received via a second route into a second electric signal. The switch circuit selects the first electric signal or the second electric signal. The terminator circuit extracts a packet from an electric signal selected by the switch circuit. The packet buffer stores the packet extracted by the terminator circuit. The clock generator generates a clock signal. The signal generator generates a continuous signal that includes the packet stored in the packet buffer by using the clock signal.

An optical transmitter, having an encoder and modulator, transmits a data signal. The encoder maps information bits of the data signal to a symbol in eight-dimensional (8D) constellation space spanned by vectors IXT1, QXT1, IYT1, QYT1, IXT2, QXT2, IYT2, QYT2, wherein I and Q are in-phase and quadrature components of an optical carrier, X and Y are orthogonal polarizations of the optical carrier, and T1 and T2 are two consecutive transmission time slots, by selecting the symbol from a set of constellation points in the 8D space. The modulator uses the symbol in the two consecutive transmission time slots to modulate two carrier waves, and to transmit the two carrier waves over the orthogonal polarizations of the optical carrier. The set of constellation points do not include any constellation point with parallel Stokes vectors in the two consecutive transmission time slots but comprise constellation points with orthogonal Stokes vectors.

A pluggable optical module according to the present invention includes a pluggable electric connector configured so as to be insertable into and removable from an optical transmission apparatus, and capable of transmitting/receiving a data signal to/from the optical transmission apparatus, a drive unit configured to output first/second driving signals by amplifying the data signal, an optical signal output unit configured to output a first/second optical signal modulated according to the first/second drive signal, a light-intensity monitoring unit configured to monitor intensities of the first/second optical signals, a control unit configured to control a gain of the drive unit so as to adjust a difference between the intensities of the first/second optical signals based on a result of the monitoring by the light-intensity monitoring unit, and a pluggable optical receptor configured so that an optical fiber can be inserted thereinto and removed therefrom, and configured to output the first/second optical signals.