Each of a first filter to a fourth filter is an FIR filter having one tap. Each of a fifth filter and a sixth filter is an FIR filter having less than 46 taps. As a result, it is possible to obtain an adaptive equalization filter having a smaller total number of taps than an adaptive equalization filter using an FIR filter having 24 taps as each of the first to fourth filters.

A skew compensation apparatus and method. In an optical system that uses optical signals, skew may be generated as the optical signals are processed from an input optical signal to at least two electrical signals representative of the phase-differentiated optical signals. A compensation of the skew is provided by including an optical delay line in the path of the optical signal that does not suffer the skew (e.g., that serves as the time base for the skew measurement). The optical delay line introduces a delay T.sub.skew equal to the delay suffered by the optical signal that is not taken as the time base. The two signals are thereby corrected for skew.

A method is presented for determining an offset frequency of a frequency comb. The method includes: generating a beam of light with a waveform that repeats regularly in the time domain and exhibits a frequency comb in the frequency domain; directing the beam of light towards a point of incidence on a material; and detecting oscillation of a photocurrent in the material that is caused by the beam of light. Of note, the beam of light has an optical bandwidth that includes light propagating at a first frequency and at a second frequency, where the first frequency is less than the second frequency and the ratio of the second frequency to the first frequency is n:m, where n=m+i, m is an integer greater than one, and n and i are positive integers. Additionally, the material has a band gap and the band gap is not more than n times the first frequency.

A method and structure for signal propagation in a coherent optical receiver device. Asynchronous equalization helps to reduce complexity and power dissipation, and also improves the robustness of timing recovery. However, conventional devices using inverse interpolation filters ignore adaptation algorithms. The present invention provides for forward propagation and backward propagation. In the forward case, the filter input signal is forward propagated through a filter to the adaptation engine, while, in the backward case, the error signal is backward propagated through a filter to the asynchronous domain. Using such forward and backward propagation schemes reduces implementation complexity while providing optical device performance.

A method and structure for equalization in coherent optical receivers. Block-based LMS (BLMS) algorithm is one of the many efficient adaptive equalization algorithms used to (i) increase convergence speed and (ii) reduce implementation complexity. Since the computation of the equalizer output and the gradient of the error are obtained using a linear convolution, BLMS can be efficiently implemented in the frequency domain with the constrained frequency-domain BLMS (FBLMS) adaptive algorithm. The present invention introduces a novel reduced complexity constrained FBLMS algorithm. This new approach replaces the two discrete Fourier transform (DFT) stages required to evaluate the DFT of the gradient error, by a simple frequency domain filtering. Implementation complexity can be drastically reduced in comparison to the standard constrained FBLMS. Furthermore, the new approach achieves better performance than that obtained with the unconstrained FBLMS in ultra-high speed coherent optical receivers.

A communication network includes a coherent optics transmitter, a coherent optics receiver, an optical transport medium operably coupling the coherent optics transmitter to the coherent optics receiver, and a coherent optics interface. The coherent optics interface includes a lineside interface portion, a clientside interface portion, and a control interface portion.

To provide a method and device capable of easily measuring the CMRR vs. frequency characteristics of an optical receiver. Light having a measurement frequency ( [hz]) is split into two different paths, and a first optical two-tone signal, which is signal light and has a frequency difference ( [hz]), and a second optical two-tone signal, which is local light and has a frequency difference (+ [hz]), are obtained and input into a coherent receiver to be measured, wherein electrical signals output from the receiver are measured to obtain both the ratio of the intensity of a signal component having the frequency [hz] to the intensity of a signal component having the frequency [hz], which corresponds to the CMRR on the signal light side, and the ratio of the intensity of a signal component having the frequency + [hz] to the intensity of the signal component having the frequency [hz], which corresponds to the CMRR on the local light side.

A transceiver having an improved transmitter optical signal to noise ratio, and methods of making and using the same.

A system for optical linear sampling and coherent detection of an optical signal OS comprises a source emitting a pulsed optical signal SP and an optical coupler that splits the pulsed optical signal SP into two replicas, the first replica of the pulsed optical signal SP is sent to a first optical hybrid circuit and the second replica of the pulsed optical signal SP is send to a second optical hybrid circuit, a source emitting an optical signal OS and optical coupler that splits the incoming optical signal OS into two replicas, the first replica of the incoming optical signal OS is sent to the first optical hybrid circuit and the second replica of the incoming optical signal OS is sent to a wavelength recovery device WVLR, whose output is a continuous-waveform optical signal CW at the central wavelength of the incoming optical signal OS, which sends it to the second optical hybrid circuit. such that the optical signal OS is sampled within the first hybrid circuit and the continuous waveform optical signal CW is sampled in the second hybrid circuit, and a device BDADC comprising balanced photodectors detecting optical signals at the output of the two optical hybrid circuits and an analog/digital converter ADC.

Presented herein are techniques to manage optical network infrastructure. A method includes inducing a predetermined vibration on a fiber optic cable, the predetermined vibration being sufficient to cause a change to at least one of a state of polarization and a phase of optical signals being carried by respective optical fibers in the fiber optic cable, detecting, at a first endpoint, using a first coherent optical receiver, and at a second endpoint, using a second coherent optical receiver, the change to the at least one of the state of polarization and the phase of the optical signals, and based on the detecting, determining that the first endpoint and the second endpoint are connected to, or in communication with, one another via at least one finer in the fiber optic cable.