Cisco Technology, Inc.

Jonas Geyer

Thomas Duthel

James E Whiteaway

Theodor Kupfer

Andreas Bernhard Bisplinghoff

Andreas Bisplinghoff

An optical transmitter may include a sample rate converter and a digital-to-analog converter operable to convert an inputted digital electrical signal to an analog optical signal. The signal converter may include a first interface operable to receive a digital electrical signal that may include a block of input data having N symbols in a time domain. The signal converter may also include: a first module operable to transform, via a Fourier Transform, the input data having N symbols from the time domain to a frequency domain; a second module operable to up-sample the N frequency domain samples so that there are 1.6N, 2N, or 2.67N frequency domain samples, for example; and then a third module operable to transform, via an inverse Fourier Transform, the 1.6N, 2N, or 2.67N frequency domain samples to an equivalent number of time domain samples at 1.6, 2.0, or 2.67 samples per symbol, respectively.

Optical communication transmitter system

Techniques are provided to estimate a distance of one received optical subchannel to one or both of its neighbor (adjacent) subchannels. An optical field comprised of a plurality of subchannels of optical signals at respective wavelengths is received on an optical fiber. Using coherent optical reception in conjunction with analog-to-digital conversion, the received optical field is converted to digital complex valued data. The digital complex valued data is transformed to the frequency domain to produce spectrum data. Using either a peak method or a gap method, a distance or spacing is computed between a subchannel of interest among the plurality of subchannels and at least one neighbor subchannel based on the spectrum data.

Digital frequency offset monitor for coherently detected optical superchannels

According to a first aspect, techniques are provided to optimize a Mach-Zehnder modulator drive waveform by distorting the outer modulation levels of the waveform, thereby equalizing eye openings of the received optical field, and in particular creating a wider and more defined central eye opening of the received optical field. According to a second aspect, techniques are provided to adjust in-phase (I) modulation levels based on the imperfect performance of a Mach-Zehnder modulator allocated to modulate quadrature-phase (Q) modulation levels, and conversely to adjust the Q modulation levels based on the imperfect performance of an MZ modulator allocated to modulate I modulation levels.

Pre-distortion techniques for optical modulators to improve constellation point separation

Carrier phase estimation techniques are provided for processing a received optical signal having a carrier modulated according to a modulation scheme. First and second carrier phase estimation operations are performed on a digital signal derived from an optical carrier obtained from the received optical signal using coherent optical reception. The first carrier phase estimation operation tracks relatively fast phase variations of the optical carrier of the received optical signal to produce a first carrier phase estimation and the second carrier phase estimation operation tracks relatively slow phase variations of the optical carrier of the received optical signal to produce a second carrier phase estimation. A difference between the first and second carrier phase estimations is computed. Occurrence of a cycle slip is determined when the difference is greater than a threshold. A correction is applied to the first carrier phase estimation when the low pass filtered difference exceeds the threshold.

Cycle slip reduction in coherent optical communications

Techniques are provided for estimation of the chromatic dispersion (CD) in an optical signal received by an optical receiver. The techniques involve iteratively adjusting dispersion compensation coefficients of one or more filters configured to compensate for the CD in the received optical signal. At each iteration of the dispersion compensation coefficient adjustment, electrical domain signals are filtered to generate digitally-filtered signals. The electrical domain signals are generated based on the received optical signal. Also at each iteration of the dispersion compensation coefficient adjustment, an amplitude histogram of the digitally-filtered signals is generated. The amplitude histograms generated at each iteration are evaluated to generate an estimate of the chromatic dispersion in the received optical signal.

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Seukendorf, Germany

Jonas Geyer