摘要:
Phase nonlinearities of an optical communications system are monitored by generating a test signal which includes a predetermined property that is uniquely associated with at least one phase nonlinearity of the optical communications system. The predetermined property of the test signal is then detected at a monitoring point of the optical communications system, and used to estimate the associated phase nonlinearity.
摘要:
A high speed D/A converter includes a phase aligner, and a vector summation block. The phase aligner operates to ensure precise phase alignment between corresponding bits of a parallel N-bit digital signal having a data rate of at least 2 GHz. The vector addition block performs a vector addition of the phase-aligned bits of the parallel N-bit digital signal. Each bit of the parallel N-bit digital signal can be weighted to ensure a correct additive contribution to the analog signal level appearing at the output of the D/A converter. Vector addition of the weighted bits can be accomplished using a microwave signal combiner network in the form of either a multistage parallel cascade of impedance matched junctions, or a linear cascade of junctions.
摘要:
A method and system for reducing non-linear signal degradation effects of WDM optical signals exacerbated by highly correlated bit patterns of optical waveforms in neighboring optical channels. Embodiments include offsetting the transmission times of signals in neighboring channels, and applying different scrambling patterns to the respective data streams prior to transmission on neighboring optical channels.
摘要:
A binary signal is encoded to produce a three-level encoded signal having reduced bandwidth and small low frequency and d.c. components, e.g. using modified duobinary encoding, the encoded signal directly modulating a semiconductor laser to produce a frequency modulated optical signal, which is passed through an interference filter to provide two-state amplitude modulation from the three-state frequency modulation for direct recovery of the binary signal by an optical receiver, the interference filter providing constructive and destructive interference for frequencies corresponding to binary one and zero bits respectively. An array transmission system can be provided by combining multiple such frequency modulated optical signals, from multiple lasers with respective central frequencies and respective encoders for multiple binary signals, using an array waveguide which also serves as a channel frequency filter, with a single interference filter. Polarization modulation instead of frequency modulation, and external modulation of an optical signal from an optical source, are also described.
摘要:
Nonlinearity-induced signal distortions are compensated by processing an input communications signal, in the electrical domain prior to Electrical-to-optical conversion and transmission through an optical link of a communications system. According to the invention, a compensation operator is determined that substantially mitigates the nonlinearity-induced signal distortions imparted to an optical signal traversing the communications system. The input communications signal is then input to the compensation operator to generate a predistorted electrical signal. This predistorted electrical signal is then used to modulate an optical source to generate a corresponding predistorted optical signal for transmission through the optical communications system. With this arrangement, arbitrary nonlinearity-induced signal distortions imparted by the optical link can be compensated in such a manner that a comparatively undistorted optical signal is obtained at the receiving end of the optical link.
摘要:
A method and system enables measurement of polarization dependent loss (PDL) in an optical communications system including a plurality of cascaded optical components. An optical signal having a predetermined initial polarization state is launched into the optical communications system. A polarization state of the signal is detected at a selected detection point downstream of the launch point. The PDE is evaluated using the predetermined initial polarization state and the detected polarization state.
摘要:
A method and system is provided for compensating polarization mode dispersion (PMD) in an optical communications system includes a controller designed to control a broadband PMD compensator to differentially delay light at each one of a plurality of selected wavelengths. At least one of the selected wavelengths lies between an adjacent pair of channel wavelengths of the optical communications system. A performance parameter value indicative of PMD is measured at each channel wavelength of the optical communications system. An estimated performance parameter value is then calculated at each selected wavelength, and an error function calculated as a function of wavelength based on the estimated performance parameter values. The broadband PMD compensator is then controlled to minimize the value of the error function.
摘要:
An optical communications system is adapted for connection to an optical fiber link of an optical communications network. The system obtains a fiber identifier respecting the optical fiber link; a respective optimum setting of one or more parameters of the optical communications system; and adjusts a respective value of each parameter in accordance with the respective optimum setting. The fiber identifier can be obtained from a value of at least one fiber transmission property of the optical fiber link. The fiber transmission property value is used to search a look-up table of class definitions, each class definition including a respective class identifier and at least one corresponding characteristic transmission property value. A class identifier is selected as the fiber identifier from the class definition for which each characteristic transmission property value most closely matches a corresponding fiber transmission property value. Each class definition may also include an optimum setting for each parameter.
摘要:
Optical dispersion imposed on a communications signal conveyed through an optical communications system is compensated by modulating the communications signal in the electrical domain. A compensation function is determined that substantially mitigates the chromatic dispersion. The communications signal is then modulated in the electrical domain using the compensation function. In preferred embodiments, compensation is implemented in the transmitter, using a look-up-table and digital-to-analog converter to generate an electrical predistorted signal. The electrical predistorted signal is then used to modulate an optical source to generate a corresponding predistorted optical signal for transmission through the optical communications system.
摘要:
A receiver is configured to detect, at a communication interface, a received signal that suffers from degradations incurred over a communication channel. The receiver applies an adaptive filter to a series of received blocks of a digital representation of the received signal, thereby generating respective filtered blocks, where each received block represents 2N frequency bins, and where N is a positive integer. The receiver calculates coefficients for use by the adaptive filter on a jth received block as a function of (i) error estimates associated with an (j−D−1)th filtered block, where D is a positive integer representing a number of blocks, and where j is a positive integer greater than (D−1); and (ii) an inverse of an approximate covariance matrix associated with the (j−D−1)th received block, where the approximate covariance matrix is a diagonal matrix of size L×L, and where L is a positive integer lower than 2N.