The present invention relates in general to communication systems, and more specifically towards methods, systems, and devices that help improve transmission rates and spectral efficiency of intensity modulated (IM) or power modulated channels utilizing multi-level pulse amplitude modulation PAM-M. In an embodiment, the present invention used an iterative algorithm to open the eyes of an eye diagram in a relatively short number of steps. The algorithm, which may not require previous characterization of the channel, utilizes pseudo-random sequences, such as PSBS15 or PRQS10, and adaptive non-linear equalizers to optimize the pre-distortion taps.

Techniques for receiving a modulated optical signal which has undergone a digital Fourier transform spreading (DFTS), include generating digital samples of the modulated optical signal, performing resampling and synchronization of the digital samples to generate time-corrected digital samples from an input wireless signal, compensating the time-corrected digital samples for nonlinearity (NL) to produce NL-compensated digital samples, de-spreading the NL-compensated digital samples using an inverse digital Fourier transform to recover quadrature amplitude modulation (QAM) modulated signals, applying post-equalization to the QAM signals to generate equalized QAM signals, performing a decision directed least mean square (DD-LMS) equalization to generate blind-optimized QAM signals and demodulating the blind-optimized QAM signals to recover data bits.

A coherent receiver includes a receive signal path including i) an input configured to connect a receive signal, ii) one or more signal paths connected to the input and to one or more optical hybrids, and iii) a variable optical attenuator (VOA) in each of the one or more signal paths; and a local oscillator (LO) signal path including i) an input configured to connect to an LO and the one or more optical hybrids, and ii) one or more complementary VOAs located between the input and the one or more optical hybrids, wherein the one or more complementary VOAs are configured to cancel any phase changes from the VOA in each of the one or more signal paths. The VOA in each of the one or more signal paths and the one or more complementary VOAs can be p-i-n junctions.

An optical receiver (20) includes an electrical signal generation unit (200), a first phase compensation unit (101), a distortion compensation unit (102), and a first dispersion compensation unit (400). The electrical signal generation unit (200) generates an electrical signal on the basis of received signal light. The first phase compensation unit (101) performs a phase rotation compensation process on the electrical signal generated by the electrical signal generation unit (200). The distortion compensation unit (102) performs a dispersion compensation process and a phase rotation compensation process in this order, at least once, on the electrical signal after having compensation performed thereon by the first phase compensation unit. The electrical signal generation unit (200), the first phase compensation unit (101), and the distortion compensation unit (102) are incorporated into one semiconductor device.

A processor circuit is provided in a coherent optical receiver module. The processor receives a series of electrical signals over a time period, representative of a series of optical signals received at instants of time within the time period. Each of the electrical signals is indicative of a respective one of a plurality of points on an IQ plane, each of the points being spaced from one of a plurality of predetermined points in the IQ plane by a corresponding one of a plurality of distortion values. In addition, the processor circuit calculates one or more perturbative coefficients based on one or more of the distortion values and determines data from the series of electrical signals based on the perturbative coefficient.

A bi-directional optical communication system employing a minimum number of single-mode high repetition rate pulsed optical signal sources to achieve cost efficiency while maintaining high data rates. The bi-directional optical communication system includes a first optical data processing unit and a second optical data processing unit. The first optical data processing unit modulates a pulsed optical source using a differential quadrature phase shift keying (DQPSK) modulation and two-level pulse amplitude (PAM-2) modulation and then demodulates it to achieve a pulse amplitude modulated signal. The second optical data processing unit reuses the same optical carrier by passing it through a regenerative wavelength converter to generate three pulsed optical carriers at different wavelengths and employs an On-off keying (OOK) modulation scheme. These carriers are employed to send uplink data at a same rate of as the downlink. As a result, large data is transmitted from one data center to another data center through a downlink and uplink free space optical link network.

An optical assembly is used for communicating laser light from a plurality of laser sources into channels for an optical network. The optical assembly comprises an optical substrate, an input optic, at least one Z-block, filters, at least one fiber collimator, and at least one delivery fiber. The input optic is disposed on the optical substrate and is configured to receive the laser light from the laser sources. The input optic is configured to collimate the laser light into a plurality of collimated laser beams. The at least one Z-block is disposed on the substrate and has an input surface and an output surface. The input surface has a plurality of filters disposed thereon, and the input surface is disposed at an angle of incidence relative to the collimated beams from the input optic. The output surface is disposed parallel to the input surface and can have at least one isolator. The at least one Z-block is configured to multiplex the collimated laser beams into at least one output signal having a plurality of the channels. At least one fiber collimator disposed on the substrate has an input and an output. The input is disposed in optical communication with the at least one Z-block and is configured to receive the output signal. The at least one delivery fiber is optically coupled to the output of the at least one fiber collimator and is configured to conduct the optical signal to a receptacle.

An optical wireless apparatus that is implemented for transmitting an optical wireless signal via an optical wireless channel includes: an electronic signal source that is configured to provide a data signal and an optical signal source that is configured to convert the data signal into the optical wireless and to emit the same. The optical wireless apparatus is configured to obtain channel information including information associated with a non-linear channel distortion of the optical wireless signal and to perform adaptation of a modulation of the optical signal source by changing an operating state of the electronic signal source for adapting the non-linear channel distortion and/or to perform adaptation of an operating point of the optical signal source for adapting the non-linear channel distortion.

A coherent optical receiver includes a plurality of components arranged in a receive signal path and a local oscillator signal path, wherein the plurality of components include one or more variable optical attenuators (VOAs) that, when actuated, generate low phase change between the receive signal path and the local oscillator signal path. With this approach, the low phase change between the receive signal path and the local oscillator signal path are substantially canceled out with some minor phase differences remaining.

An optical device includes a light source and diffuser, such as non-linear material, to form a supercontinuum of light energy of different wavelengths. An optical channel generator forms channels from the supercontinuum and forwards a multiplexed signal carrying the channels. The signal travels to an optical receiver through an optical fiber. The optical receiver identifies a non-linear penalty associated with forwarding the multiplexed signal on the optical fiber. The optical receiver modifies attributes of the received channels, such as increasing the magnitude of one of the channels, to cancel out the non-linear penalty.