A method of transmitting a data signal using an optical transmitter of an optical communications system. A first encoder processes an N-bit input vector in accordance with a first mapping to generate a corresponding M-bit data stream. A Forward Error Correction encoder processes the M-bit data stream in accordance with a predetermined FEC encoding scheme to generate an encoded signal. A constellation mapper maps the encoded signal to symbol values in accordance with a predetermined modulation scheme to generate a corresponding symbol stream. A modulator modulates a carrier light in accordance with the encoded symbol stream to generate an optical signal for transmission through the optical communications system. The first mapping can be adjusted to maximize performance of the optical communications system.

An apparatus comprising a semiconductor chip that comprises an optical modulator configured to modulate an optical signal based on a received driver signal, a voltage-mode (VM) driver coupled to the optical modulator and configured to produce a level-shifted driver signal to modulate the optical signal, and a two-stage test interface coupled to the optical modulator and configured to receive and test the level shifted driver signal. The two-stage test interface comprises a voltage equalization stage coupled to an output-terminated buffer stage, the VM driver comprises a two-stage VM Mach-Zehnder modulator (MZM) driver that comprises a pre-driver coupled to a VM level-shifter (VMLS). The apparatus further comprises a resistor coupled to an output of the buffer stage, wherein the resistor comprises an amount of resistance that matches a termination resistance of a test equipment. The termination resistance is about 50 ohm ().

Provided are a method and an apparatus for generating and transmitting feedback signals for a plurality of reference signals having different directionality, in a wireless communication system. A terminal may receive the plurality of reference signals having different directionality, and transmit, to a transmission end, a feedback signal including a beam index which indicates one of the plurality of reference signals.

Methods, systems, and devices for wireless communication are described. One method includes identifying a plurality of intermediate precoders corresponding to a plurality of tone subsets. The plurality of intermediate precoders define a plurality of vectors across the plurality of tone subsets. The method further includes selecting, for each vector of the plurality of vectors, a subset of non-frequency domain components of the vector, such as time-domain components; modifying the plurality of intermediate precoders to a plurality of smoothed precoders based at least in part on the selected subset of non-frequency domain components for each vector; and precoding a plurality of transmit streams using the plurality of smoothed precoders. The plurality of smoothed precoders is smoothed in a frequency domain compared to the plurality of intermediate precoders. Smoothing precoders may enable application of wideband channel estimation techniques using user equipment (UE)-specific reference signals.

A high-speed signal generator. A digital signal processing (DSP) block generates a set of N (where N is an integer and N2) parallel digital sub-band signals, each digital sub-band signal having frequency components within a spectral range between 0 Hz and Fs/2. A respective Digital-to-Analog Converter (DAC) processes each digital sub-band signal to generate a corresponding analog sub-band signal, each DAC having a sample rate of Fs. A combiner combines the analog sub-band signals to generate an output analog signal having frequency components within a spectral range between 0 Hz and NFs/2.

An optical modulator for generating quadrature amplitude modulation (nQAM) and phase-shift keying (nPSK) signals with tunable modulation efficiency. The modulator includes a controlling circuit for adjusting the modulation efficiency or modulation depth of the modulator by controlling the direct current (DC) bias.

Consistent with the present disclosure a transmitter is provided that transmits data in either a quasi-DP-BPSK (QDP) mode or in a DP-QPSK mode. In the QDP mode, data bits are transmitted as changes in phase between first and second phase states along a first axis or as changes in phase between third and fourth phase states along a second axis in the IQ plane. Although the transmitter outputs an optical signal that changes in phase between each of the four states, a sequence bit identifies which axis carries the data bit. The sequence bit is one of a series of sequence bits that may be generated by a pseudo-random number generator. The series of sequence bits can be relatively long, e.g., 32 bits, to permit sufficiently random changes in the axis that carries the data. Thus, unlike conventional BPSK, in which data is transmitted between phase states along a single axis, the present disclosure provides an apparatus and related method for randomly selecting one of two axes, for example, for each transmitted bit. In the receiver, it has been observed that the MU-CMA algorithm can process data carried by optical signals in the QDP mode with relatively few errors. Thus, the same equalizer (FIR) filter may be used to process BPSK, as well as QPSK data.

Disclosed herein is a dual parallel Mach-Zehnder-modulator (DPMZM) device comprising a DPMZM 10 having first and second inner MZMs arranged parallel to each other. The first inner MZM generates an in-phase component E.sub.I of an optical signal in response to a first driving voltage V.sub.I, and the second inner MZM generates a quadrature component E.sub.Q of said optical signal in response to a second driving voltage V.sub.Q. Further disclosed is a calculation unit 52 configured for receiving an in-phase component y.sub.I and a quadrature component y.sub.Q.sub._ of a desired base-band signal, and for calculating pre-distorted first and second driving voltages V.sub.I, V.sub.Q. The calculation of the pre-distorted first and second driving voltages V.sub.I, V.sub.Q is based on a model of said DPMZM 10 accounting for I-Q cross-talk, and using an algorithm that determines said first and second driving voltages V.sub.I, V.sub.Q each as a function of both of said in-phase and quadrature components y.sub.I, y.sub.Q of said base-band signal.

An optical transmitter may receive and encode a first group of bits into first encoded data and second encoded data. The optical transmitter may supply a first sub-carrier carrying a first symbol and a second sub-carrier carrying a second symbol. The first symbol and the second symbol may be based on the first encoded data and the second encoded data, respectively, such that the first sub-carrier has a first polarization state comprising first and second polarization components, and the second sub-carrier has a second polarization state comprising first and second polarization components. The first polarization state may be substantially orthogonal to the second polarization state. An optical receiver may receive the first symbol via the first sub-carrier, may receive the second symbol via the second sub-carrier, may decode the first symbol and the second symbol into a second group of bits, and may output the second group of bits.

In a system for converting digital data into a modulated optical signal, an electrically controllable device, including a modulator having one or more actuating electrodes, provides an analog-modulated optical signal that is modulated in response to output data bits of a digital-to-digital mapping. A digital-to-digital conversion provides the mapping of input data words to the output data bits. The mapping enables adjustments to correct for non-linearities and other undesirable characteristics, thereby improving signal quality.