A method and apparatus for compensating optical dispersion over an optical fiber are provided in fiber optic communications to increase a transmission distance by overcoming the optical dispersion caused by wavelength changes of light sources and dispersion effects of a fiber. In one implementation, the present technology may be implemented in the form of a RLC passive microwave filter with no extra power consumption. By way of example, an optical receiver may include a photodiode operable to receive an optical signal and produce an electrical signal, a transimpedance amplifier (TIA) operable to receive the electrical signal and produce a first amplified signal, and an electronic dispersion compensation (EDC) device operable to receive the first amplifier signal from the TIA and compensate or reduce the effects of optical dispersion on the received electrical signal.

A method and apparatus for compensation of a chromatic dispersion through an optical compensation and an electronical compensation in optical communication. An optical communication method receives an optical signal, estimates a first transmission length based on a null component included in a frequency spectrum of the optical signal, optically compensates for a chromatic dispersion of the optical signal based on the first transmission length, estimates a second transmission length based on a null component included in a frequency spectrum of the compensated optical signal, and electronically compensates for a residual chromatic dispersion of the compensated optical signal based on the second transmission length.

Apparatus and method for digital signal constellation transformation are provided herein. In certain configurations, an integrated circuit includes an analog front-end that converts an analog signal vector representing an optical signal into a digital signal vector, and a digital signal processing circuit that processes the digital signal vector to recover data from the optical signal. The digital signal processing circuit generates signal data representing a signal constellation of the digital signal vector. The digital signal processing circuit includes an adaptive gain equalizer that compensates the signal data for distortion of the signal constellation arising from biasing errors of optical modulators used to transmit the optical signal.

In a method in which a compensation coefficient calculating portion (6) calculates a compensation coefficient of a compensation portion (5) which compensates transmission characteristics of a signal, a known signal is extracted from the signal. Next, a pseudo-random number is added to the extracted known signal. Next, the compensation coefficient is calculated by comparing a true value of the known signal with the known signal to which the pseudo-random number is added.

A coherent optical reception device includes a local oscillation laser that supplies laser light, a coherent optical reception front-end unit that receives a multi-level modulated optical signal, demodulates the optical signal on the basis of the laser light, and converts a demodulated optical signal into an electrical analog signal, an analog-to-digital converter that converts the analog signal into a digital signal, a compensation unit that compensates for an influence of dispersion due to a wavelength or a polarized wave of the optical signal and recovers a carrier phase of the digital signal, a constellation distortion compensation unit that compensates for constellation distortion of the multi-level modulation included in the digital signal in which an influence of dispersion is compensated for by the compensation unit, and an error correction decoding unit that performs error correction of the digital signal in which the constellation distortion is compensated for.

A method decodes an optical signal transmitted over an optical channel from a transmitter to a receiver. The method produces, from the transmitted optical signal, a digital signal including received data symbols and received pilot symbols and determines phase noise on the pilot symbols using a statistical probability distribution of phase noise on the optical channel and errors between phases of the received pilot symbols and the transmitted pilot signals. The method estimates phase noise on the data symbols using an interpolation of the phase noise on the pilot symbols and compensates the digital signal with the phase noise on the data symbols to produce a filtered signal with an equalized phase. The method demodulates and decodes the filtered signal to produce an estimate of the transmitted optical signal.

A WDM receiver configured to apply electronic equalization processing to both dispersion-compensated and dispersion-distorted versions of the received communication signal. In an example embodiment, the receiver's DSP first generates an equalized dispersion-compensated signal corresponding to the communication signal. The DSP then performs electronic dispersion-application processing on the equalized dispersion-compensated signal to generate a dispersion-distorted version thereof. The DSP then applies decision-aided electronic equalization processing to the dispersion-distorted version of the signal, subjects the resulting equalized signal to another round of dispersion-compensation processing, and recovers the data encoded in the communication signal using the resulting dispersion-compensated signal. This chain of signal processing tends to be effective in reducing nonlinear distortions of the intra-channel type and also some effects of nonlinear inter-channel interference, which advantageously enables the WDM receiver to support a lower BER and/or a higher data-transport capacity than those achievable with conventional WDM receivers.

It are provided an optical communication system and an optical communication method. The system comprising at least two optical channels for communicating optical data signals; at least one optical filter arrangement for compensating distortions of the optical data signals communicated via the optical channels and/or crosstalk between the optical channels. The optical filter arrangement comprises at least one optical filter assigned to one of the optical channels and at least one optical filter assigned to the other one of the optical channels, wherein each one of the optical filters is configurable in such a way that different wavelength components of an incoming optical signal will be modified individually.

A system has a plurality of non-linear circuit stages and an intervening linear circuit stage. An input signal is provided to a first non-linear circuit stage, and from the first non-linear circuit stage, to the linear circuit stage. The first non-linear circuit stage applies a second-order distortion to the input signal and provides the resulting signal to the linear circuit stage. The resulting signal that is output from the linear circuit stage is inverted with respect to the input signal and suitably linearly processed (attenuated or amplified). This signal is then provided to a second non-linear circuit that applies a second-order distortion and outputs a signal that has an overall reduction in second-order distortion.

The present disclosure relates to an apparatus and method of processing a digital signal, wherein an input signal is transformed into the frequency domain by applying a fast Fourier transformation (FFT) processing to obtain a transformed input signal. Positive and negative frequency components of the transformed input signal are separated and respective ones of the separated positive and negative frequency components are separately processed by respective digital filtering to obtain filtered frequency components. The filtered frequency components are combined in the frequency domain using a down-sampling operation for down-sampling the filtered frequency components from an input number of samples per symbol to a different output number of samples per symbol, and the combined output components are converted into the time domain by applying an IFFT processing.