Multilevel optical intensity modulation high in accuracy is performed using electro-absorption optical modulators. There is provided a plurality of EA modulators connected in series in a path of an optical signal from a light source, and a multilevel-coded modulated optical signal is generated by modulating an intensity of an input optical signal from the light source based on a modulation signal using the EA modulators. Each of the EA modulators is switched between an ON state and an OFF state of optical absorption in accordance with the modulation signal. Regarding an extinction ratio of the ON state to the OFF state in each of the EA modulators, the EA modulators have respective values difference from each other, and are arranged in ascending order of the extinction ratio from the light source side.

A circuit and method for mitigating multi-path interference in direct detection optical systems is provided. Samples of an optical signal having a pulse amplitude modulated (PAM) E-field are processed by generating a PAM level for each sample. For each sample, the sample is subtracted from the respective PAM level to generate a corresponding error sample. The error samples are lowpass filtered to produce estimates of multi-path interference (MPI). For each sample, one of the estimates of MPI is combined with the sample to produce an interference-mitigated sample.

A system for converting digital data into a modulated optical signal, comprises an electrically controllable device having M actuating electrodes. The device provides an optical signal that is modulated in response to binary voltages applied to the actuating electrodes. The system also comprises a digital-to-digital converter that provides a mapping of input data words to binary actuation vectors of M bits and supplies the binary actuation vectors as M bits of binary actuation voltages to the M actuating electrodes, where M is larger than the number of bits in each input data word. The digital-to-digital converter is enabled to map each digital input data word to a binary actuation vector by selecting a binary actuation vector from a subset of binary actuation vectors available to represent each of the input data words.

A device including a remote control of remote operation of the device is described. The remote control includes a key matrix and a microprocessor. The microprocessor processes key scan codes from the key matrix and converts the key scan codes to amplitude modulated remote control commands for transmission by a wireless transmitter. The device includes components so that a user can operate the device locally without a remote control. The components in the device that enable local operation of the device are comparable to components in the remote control that enable remote operation of the device so that a minimum of changes are required in the device to enable local operation of the device.

An optical transmission device includes an optical modulator and a processor. The optical modulator optically modulates an optical signal with a driving signal to output a modulated optical signal. The processor performs ABC on a bias of the optical modulator, using the modulated optical signal, so as to cause the bias to converge to an optimum point. The processor starts the ABC using a modulated optical signal optically modulated with a QPSK signal at start-up timing, acquires an optimum value that is a bias value when the bias converges to the optimum point, and stops the ABC. After the ABC is stopped, the processor sets the acquired optimum value as an initial value, and restarts the ABC using a modulated optical signal optically modulated with an N-QPSK signal.

An optical transmitter and a method of producing a low-photon-density modulated optical signal are disclosed. The optical transmitter and method include an optical source configured to emit a continuous optical carrier waveform, a dilation module configured to apply a spreading code to a data payload to spread each of the plurality of symbols in time to expand the symbol duration by a dilation factor and produce a corresponding plurality of time-dilated symbols, the plurality of time-dilated symbols having a lower photon density than the plurality of symbols; a mapping module configured to map the plurality of time-dilated symbols to a modulation scheme; and a modulator configured to modulate the optical carrier waveform with the plurality of time-dilated symbols according to the modulation scheme to produce the low-photon-density modulated optical signal encoded with the plurality of time-dilated symbols corresponding to the data payload.

An optical modulator includes an optical waveguide including at least a first PN junction phase shifter and a second PN junction phase shifter. A driver circuit drives operation of the first and second PN junction phase shifters in response to a pulse amplitude modulated (PAM) analog signal having 2.sup.n levels. The PAM analog signal is generated by a digital to analog converter that receives an n-bit input signal. In an implementation, the optical waveguide and PN junction phase shifters are formed on a first integrated circuit chip and the driver circuit is formed on a second integrated circuit chip that is stacked on and electrically connected to the first integrated circuit chip.

A system and method including multi-dimensional coded modulation wherein symbols within successive blocks of symbols are mapped using at least two different constellations to differentiate the symbols from each other. At least one data bit is encoded by an order of the symbols within each block of symbols. The receiver decodes the data by decoding at least one bit from the order of the symbols mapped with the first and second constellations.

The present disclosure provides methods and devices that use the RIS phase shifting ability to provide many degrees of freedom to enable data to be overlaid on transmitted signals. The data overlay is done while the RIS is still beamforming the signal towards the receiver(s). The phase shifting capabilities of the RIS elements can provide amplitude, phase, frequency, and polarization manipulations. These manipulations can help enhance the communication and provide the ability to overlay information. The present application also provides new configuration signaling among devices in a communication network utilizing the RIS and configuration for the RIS.

An optical receiver, e.g., for an Optical Supervisory Channel (OSC), whose optical front end comprises a polarization-diversity coherent optical receiver configured to receive a conventional intensity-modulated (e.g., OSC) signal. Four quadrature components of the received OSC signal detected by the polarization-diversity coherent optical receiver are sampled at a relatively high sampling rate and are used to calculate the Stokes parameters of the OSC signal. As a result, the Stokes parameters can be updated at the high sampling rate, which can be suitably selected to enable polarization tracking with a relatively high time resolution and/or at relatively high SOP-rotation speeds. The four detected quadrature components are appropriately combined in the receiver DSP to determine the intensity of the received OSC signal, which is then used in a conventional manner to recover the OSC data encoded therein.