| Patent application number | Description | Published |
|---|
| 20090201796 | LOW CONVERSION RATE DIGITAL DISPERSION COMPENSATION - A method of suppressing effects of aliasing in a system for digitally processing a high speed signal having a symbol rate of 1/T. The high speed signal is sampled at a fractional multiple (N) of the symbol rate, wherein 1| 08-13-2009 | |
| 20100067902 | OPTICAL TRANSMITTER ERROR REDUCTION USING RECEIVER FEEDBACK - Described is a method of reducing transmitter error in an optical communications channel. An optical signal transmitted from an optical transmitter that has impairment due to transmitter error is processed to generate a digitally-equalized signal. A nonlinear characteristic of the digitally-equalized signal that relates to the transmitter error is determined. An optical control signal comprising data that are based on the nonlinear characteristic is transmitted to the optical transmitter. The optical transmitter modifies a transmitter parameter in response to the optical control signal to change the nonlinear characteristic and thereby reduce the impairment. | 03-18-2010 |
| 20100092181 | LOW CONVERSION RATE DIGITAL DISPERSION COMPENSATION - A method of suppressing effects of aliasing in a system for digitally processing a high speed signal having a symbol rate of 1/T. The high speed signal is sampled at a fractional multiple (N) of the symbol rate, wherein 1| 04-15-2010 | |
| 20100254702 | CLOCK RECOVERY WITH CHANNEL COEFFICIENTS - In a coherent optical receiver of an optical communications network, a method of recovering a clock signal from a high speed optical signal received through an optical link. A set of compensation vectors are adaptively computed for compensating Inter-symbol Interference (ISI) due to at least polarization impairments of the optical signal. A channel delay is estimated based on the computed compensation vectors. The estimated channel delay is subtracted from the computed compensation vectors to generate corresponding modified compensation vectors. Finally, the modified compensation vectors are used to derive a recovered clock signal. | 10-07-2010 |
| 20110255875 | DUAL RATE QPSK/TCM-QPSK OPTICAL MODULATION - The present disclosure allows for optical link capacity to be optimized based on transmission parameters, such as amplifier gain, link loss, optical signal-to-noise ratio. For example, optical signals at wavelengths that are susceptible to impairments, such as non-linear effects, or that are not adequately amplified by an optical amplifier, may be modulated in accordance with lower rate/less spectrally efficient modulation formats (“low rate formats”) that are more noise tolerant. On the other hand, those optical signals at wavelengths that are less susceptible to or do not incur such impairments may be modulated in accordance with highly spectrally efficient /higher rate modulation formats (“high rate formats”) that are more noise sensitive. Accordingly, a maximum or optimized capacity may be realized through appropriately choosing, for each channel, a particular modulation format and channel spacing. Such optimized capacity can be readily obtained with adaptive driver circuits. | 10-20-2011 |
| 20110274436 | OPTICAL COMMUNICATION SYSTEM - Consistent with the present disclosure a transmitter is provided that transmits data in either a “quasi-DP-BPSK” (“QDP”) mode or in a DP-QPSK mode. In the QDP mode, data bits are transmitted as changes in phase between first and second phase states along a first axis or as changes in phase between third and fourth phase states along a second axis in the IQ plane. Although the transmitter outputs an optical signal that changes in phase between each of the four states, a sequence bit identifies which axis carries the data bit. The sequence bit is one of a series of sequence bits that may be generated by a pseudo-random number generator. The series of sequence bits can be relatively long, e.g., 32 bits, to permit sufficiently random changes in the axis that carries the data. Thus, unlike conventional BPSK, in which data is transmitted between phase states along a single axis, the present disclosure provides an apparatus and related method for randomly selecting one of two axes, for example, for each transmitted bit. In the receiver, it has been observed that the MU-CMA algorithm can process data carried by optical signals in the QDP mode with relatively few errors. Thus, the same equalizer (FIR) filter may be used to process BPSK, as well as QPSK data. | 11-10-2011 |
| 20110291865 | METHOD, SYSTEM, AND APPARATUS FOR INTERPOLATING AN OUTPUT OF AN ANALOG-TO-DIGITAL CONVERTER - A system, method, and apparatus is disclosed for interpolation of an output of an analog to digital converter (ADC) to enable operation of the ADC at a sampling rate that is independent of the sampling rate for a DSP core so as to efficiently enable operation at higher date rates. According to one of the embodiments, an interpolation circuit is coupled between the ADC and DSP core and receives a first plurality of samples of data at the first data rate from the ADC and supplies a plurality of samples of second data at a second data rate to the DSP core; the second data rate being less than the first data rate. According to one of the embodiments, the interpolation circuit includes a memory and a FIR filter circuit having filter tap coefficient values selected to provide attenuation at high frequencies to reduce aliasing noise. | 12-01-2011 |
| 20110318017 | METHOD, SYSTEM, AND APPARATUS FOR CARRIER SYNCHRONIZATION OF QAM MODULATED SIGNALS - Consistent with the present disclosure, optical signals are modulated in accordance with a higher order QAM modulation format, such as 8-QAM, to carry customer data, for example. The optical signals are converted to corresponding electrical signals, which are then subject to further processing. In particular, phase data associated with the higher order QAM constellation is processed, such that the outer points of the constellation are rotated to have the same phase as the inner points. As a result, both the inner and outer points resemble a constellation, and both may be more readily processed using feedforward or feedback carrier recovery. After such carrier recovery, the phase data is further processed so that the outer points are rotated back and the customer data can be extracted from the phase data. | 12-29-2011 |
