Huawei Technologies Co., Limited

Ciena Corporation

Xuefeng Tang

Zhiping Jiang

Zhuhong Zhang

Chuandong Li

Wing Chau Ng

Jianhong Ke

Junho Chang

Maurice M O'Sullivan

Michael Andrew Reimer

Douglas James Beckett

Jincan Cao

Hossein Najafi

Haitao Sun

Ahmed Mohamed Medra

Ali Bakhshali

Nourhan Eid

Sung Chung

Meng Qiu

Ge Gao

Jianwu Wang

Hongliang Li

Qingyi Guo

Si Ouyang

Qiang Jin

Device and methods for real-time polarization-dependent loss monitoring at coherent transceivers. In one embodiment, there is provided a method of monitoring a polarization dependent loss (PDL) of a signal during transmission through an optical communication link, the method comprising: receiving the signal by a coherent receiver, the received signal being subjected to one or more impairments in Amplifier Gain Control (AGC) mode, the one or more impairments including PDL; estimating an AGC gain effect of the AGC mode; compensating for the AGC gain effect in the received signal; determining the PDL from the compensated signal; and reporting the PDL.

Device and methods for real-time polarization-dependent loss monitoring at coherent transceivers

The disclosed systems and methods for determining spectrum-resolved signal-to-noise ratio (SNR) in an online dense wavelength division multiplexing (DWDM) optical link, the method comprising: i) receiving a noise affected optical signal; ii) converting the received optical signal into a digital signal; iii) processing the digital signal to extract the noise affected transmitted signal; iv) decoding the noise-affected transmitted signal and reconstructing an original transmitted signal; v) converting the noise-affected transmitted signal into frequency domain noise-affected transmitted signal; vi) converting the original transmitted signal into frequency domain original transmitted signal; vii) selecting spectrum slices from the frequency domain noise-affected transmitted signal and the frequency domain original transmitted signal; viii) converting the spectrum slices into time domain portions of the noise-affected transmitted signal and the original transmitted signal respectively; ix) correlating the time domain portions of the noise-affected transmitted signal and the original transmitted signal; and x) determining the spectrum-resolved SNR.

Systems and methods for determining spectrum resolved SNR in an online dense wavelength division multiplexing optical link

Pre-compensation for linear and non-linear distortion in data symbols comprises generating a set of data symbols to be transmitted and converting the set into a set of frequency-domain samples, which are then pre-processed. Linear distortion compensation is provided, prior to compensating for non-linear distortions, to the pre-processed set of frequency-domain samples. The linear distortion compensated set of frequency-domain samples is converted into a linear distortion compensated set of time domain samples. Non-linear distortion compensation is provided to the linear distortion compensated set of time domain samples. A Pattern Dependent Lookup Table (PDLUT) is generated by receiving consecutive sequences of samples included in a set of time domain samples, quantizing the consecutive sequences of samples into integer-valued consecutive sequences of samples, computing error correction values corresponding to the integer-valued consecutive sequences of samples, and storing the indexes of integer-valued consecutive sequences of samples and the corresponding error correction values in the PDLUT.

Method and system for pre-compensating non-linear distortion in data samples

The disclosed systems, and methods are directed to compressing a Pattern Dependent Look-up Table (PDLUT) including distortion correction values corresponding to data symbol sequences, including: i) symmetrically rearranging the data symbol sequences and the associated distortion correction values; ii) folding and amplitude reversing a second half of the rearranged data symbol sequences and the associated distortion correction values; iii) determining approximate distortion correction values for a first half of the rearranged data symbol sequences based on the distortion correction values associated with the first half of the rearranged data symbol sequences and the folded and amplitude reversed distortion correction values associated with the second half of the data symbol sequences; and iv) updating the PDLUT based on the approximate distortion values corresponding to the first half of the rearranged data symbol sequences.

Method and system for compressing and employing pattern dependent look-up table

Methods and devices for IQ time skew and conjugation compensation and calibration of a coherent transmitter or transceiver are described. A pilot tone is combined with a digital data signal such that relative powers of the pilot tone in each of two frequency bands of the transmitted data signal may be detected by a pilot tone detector and used to calculate the time skew between I and Q modulation channels of the transmitter. A transmitter DSP applies IQ time skew bias to the data signal to compensate for any calculated IQ time skew. The pilot tone detector also provides the transmitter DSP with the information necessary to detect phase conjugation of the optical signal, which can be corrected by inverting the polarity of the data signal or changing the phase bias point of the optical modulator.

Self-calibrating device and method for in-phase and quadrature time skew and conjugation in a coherent transmitter

The disclosed systems and methods for frequency domain (FD) local oscillator frequency offset (LOFO) compensation. The method comprising: i) compensating, by an integer Fast Fourier Transform (FFT) bins-based oscillator, LOFO in a received signal by an integer number of FFT bins; and ii) compensating, by a fractional FFT bins-based oscillator, LOFO in the compensated signal by the integer FFT bins-based oscillator with a fine compensation resolution of a fractional number of FFT bins.

Systems and methods for frequency domain local oscillator frequency offset compensation

Apparatuses and methods for far-end monitoring of transmitter IQ skew in a DSCM system are described. Soft symbols for a given subchannel and a corresponding mirror subchannel are used as joint inputs to a MIMO equalizer. The hard decision symbols for the given subchannel and mirror subchannel are used as references to compute the equalizer coefficients. An estimated phase or estimated transmitter IQ skew is computed for at least the given subchannel using the equalizer coefficients. The computation is repeated to obtain estimated phase or estimated transmitter skew for all subchannels. The transmitter IQ skew is computed using the estimates from all subchannels. The computation is performed for each polarization. The computed transmitter IQ skew is communicated back to the transmitter via optical path (for correcting the skew).

Apparatuses and methods of far-end transmitter skew monitoring in digital subcarrier multiplexing systems

The disclosed systems and methods for detecting mirror crosstalk between frequency bands equally above and below the center frequency of a Digital Subcarrier Multiplexing system include: a transmitter configured to insert zero-power symbols on half the frequency bands below center frequency, and insert other zero-power symbols, partially overlapping in time with the first zero-power symbols, on the other half of the frequency bands above center frequency. A receiver zeroes out ASE and other noises during the overlapping portion of all the zero-power symbols, then uses the power detected during the remaining portion of each zero-power symbol in each frequency band to accurately evaluate the mirror crosstalk from the corresponding frequency band on the opposite side of center frequency.

Transmitter and receiver for mirror crosstalk evaluation and methods therefor

Methods and systems for performing signal pre-correction of a transmission signal comprising a sequence of symbols using a Pattern Dependent Look-up Table (PDLUT) containing one or more distortion correction values. Upon accessing a distortion correction value from the PDLUT for a symbol of the sequence of symbols, the accessed distortion correction value is quantized into one or more quantized values according to one or more quantizations, thereby reducing the bit-width of the distortion correction value. The transmission signal and the distortion correction value with reduced bit-width may undergo linear correction compensation, such as through a finite impulse response (FIR) filter, independent of one another, where the one or more quantized correction values with reduced bit-width reduce a number of calculation steps performed during linear correction compensation resulting in power savings. The linearly compensated quantized values and the linearly compensated signal are combined to form a pre-corrected signal.

Method and apparatus of low-complexity pattern dependent lookup table pre-compensation

Methods and apparatus for coherent transmitter calibration are provided that employ direct detection (DD) using one single photodetector (PD). The provided method and apparatus do not require hardware for coherent reception, or additional ADCs for quality control. An additional optical tone is added to a QAM optical signal that is outside the band of the QAM optical signal. The result of this is that after direct detection, there is a correlation between the real and imaginary parts, and the imaginary part can be recovered with a Hilbert transform. The estimated QAM optical signal obtained by direct detection is used to perform a transmitter factory calibration method to calibrate for one or more transmitter impairments and/or to perform in-line self-calibration.

Method and apparatus for coherent transmitter calibration

Methods and apparatuses for IQ time skew calibration in a coherent transceiver are described. A four-channel signal is received. A set of inputs is constructed for a 4&#xd7;8 MIMO equalizer by converting the four-channel signal into four complex inputs that each have a phase shift corresponding to an estimated carrier frequency offset. The set of inputs further includes conjugate replicas of the four complex inputs. Using output from the 4&#xd7;8 MIMO equalizer, equalizer coefficients are calculated by minimizing error between the MIMO output and a reference signal. Receiver and transmitter IQ skew are estimated using the equalizer coefficients, by converting the equalizer coefficients form the time domain to the frequency domain to determine receiver and transmitter IQ differential phase responses, which are indicative of respective receiver and transmitter IQ skew in the time domain. Skew compensation is then performed.

Apparatus and method for in-phase and quadrature skew calibration in a coherent transceiver

Optical transmitters, receivers, and methods are described in an optical network. An optical transmitter comprises an encoder configured to receive an input data stream and to encode the input data stream into a signal. The signal is defined as a sequence of regular units, and a rotator is configured to receive each unit of the signal and to output, for each given input unit with an input state of polarization (SOP), a respective given output unit associated with an output SOP. The output SOP of the given output unit is different from a corresponding output SOP of each other output unit that is immediately adjacent to the given output unit. The output SOPs of the units in a transmitted signal may form an alternating pattern (or other repeating pattern), which may help to lower the average BER, in particular, due to forward error correction (FEC).

Systems and methods in an optical network

The disclosed systems, apparatuses and methods are directed to controlling a difference between a first center frequency of a first optical subcarrier and a second center frequency of a second optical subcarrier of an optical super-channel signal in an optical network. The method comprises modulating the first optical subcarrier at a first optical side component frequency with a first side modulation frequency and modulating the second optical subcarrier at a second optical side component frequency with a second side modulation frequency. The method further comprises detecting a radio-frequency (RF) power at a modulated beat frequency tone in the modified optical signal.

Method and apparatus for laser frequency control

The disclosed systems, structures, and methods are directed to monitoring performance of optical networks. Transmitted and received optical channel signal has both low-power gaps and an amplitude modulation pilot tone applied. The low-power gaps are applied at a gap frequency with gap power being lower than a signal power of the optical channel signal. The pilot tone is applied to the optical channel signal at a pilot tone modulation frequency, which is different from the gap frequency. Described methods include determining pilot tone modulation depth based on detected gap power in low-power gaps of the received optical channel signal. Amplifier spontaneous emission and nonlinear noise in optical link are detected separately. This permits determining and monitoring of optical signal-to-noise ratio.

Monitoring performance of optical network using low-power gaps and a pilot tone

In a powered device (PD), four MOSFETs are used in a rectifier circuit. The four MOSFETs are disposed based on a premise that an electric potential of a contact pair 1-2 is lower than that of a contact pair 3-6 and an electric potential of a contact pair 7-8 is lower than that of a contact pair 4-5, so that a PoE current of each contact group passes through only two of the MOSFETs but does not pass through a diode.

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Kanata, Canada

Xuefeng Tang