Chromatic Dispersion Estimation for Digital Coherent Optical Receivers

Patent metadata

Field	Value
Publication number	US-2016142153-A1
Application number	US-201414546976-A
Country	US
Kind code	A1
Filing date	Nov 18, 2014
Priority date	Nov 18, 2014
Publication date	May 19, 2016
Grant date	—

Abstract

An apparatus comprises a front end configured to receive an optical signal, and convert the optical signal into a plurality of digital signals, and a processing unit coupled to the front end and configured to determine a best-match chromatic dispersion (CD) estimate in the optical signal by optimizing a cost function based on signal peaks of the plurality of digital signals.

First claim

1 . An apparatus comprising:
a front end configured to:
receive an optical signal; and
convert the optical signal into a plurality of digital signals; and
a processing unit coupled to the front end and configured to determine a best-match chromatic dispersion (CD) estimate associated with the optical signal by minimizing accumulations of peaks of each component of the plurality of digital signals.

2 . The apparatus of claim 1 , wherein the processing unit is further configured to:
generate a plurality of digital filters, each configured to compensate one of a plurality of CD candidate values; apply at least some of the plurality of digital filters to the plurality of digital signals to produce filtered signals; and compute a cost for each CD candidate value from the filtered signals according to cost function representing the accumulations of peaks.

3 . The apparatus of claim 2 , wherein the plurality of CD candidate values ranges from a minimum CD candidate value to a maximum CD candidate value, and wherein the minimum CD candidate value and the maximum CD candidate value are associated with an optical network configuration.

4 . The apparatus of claim 2 , wherein, to optimize the cost function, the processing unit is further configured to search for a minimum cost value over the costs, and wherein, to determine the best-match CD estimate, the processing unit is further configured to set the best-match CD estimate to a corresponding CI) candidate value that produces the minimum cost value.

5 . The apparatus of claim 2 , wherein the plurality of digital signals comprise one or more polarization components, each comprising an in-phase (I) component and a quadrature-phase (Q) component, wherein each digital filter is applied to the I component and the Q component of each polarization component, wherein the filtered signals produced by each filter comprise a real component and an imaginary component, and wherein, to compute the costs for the CD candidate values, the processing unit is further configured to accumulate a maximum signal peak magnitude of each of the real component and the imaginary component of each polarization component for each CD candidate value.

6 . The apparatus of claim 5 , wherein the plurality of digital filters are frequency domain filters, and wherein the processing unit is further configured to:
transform each polarization component into frequency domain signals prior to applying the plurality of digital filters; and transform each filtered signal into a time domain signal prior to computing the costs.

7 . The apparatus of claim 5 , wherein the processing unit is further configured to compute an optimum filter for each polarization component according to the best-match CD estimate such that the optimum filter compensates a CD effect of the best-match CD estimate in a corresponding polarization component.

8 . The apparatus of claim 1 , wherein the optical signal comprises a binary phase shift keying (BPSK) signal, a quadrature phase shift keying (QPSK) signal, an eight quadrature amplitude modulation (8-QAM) signal, a sixteen quadrature amplitude modulation (16-QAM) signal, or combinations thereof.

9 . The apparatus of claim 1 , wherein the optical signal comprises a raised-cosine (RC) signal, a root-raised-cosine (RRC) signal, a non-return-to-zero (NRZ) signal, a return-to-zero with 67 percent duty cycle (RZ67) signal, or combinations thereof.

10 . The apparatus of claim 1 , wherein the processing unit is a digital signal processor (DSP).

11 . The apparatus of claim 1 , wherein each digital signal in the plurality of digital signals is an electrical signal.

12 . A method for estimating chromatic dispersion (CD) in an optical device coupled to an optical transmission link, the method comprising:
receiving an optical signal via the optical transmission link; converting the optical signal into a plurality of digital signals; and determining a best-match CD estimate associated with the optical signal by minimizing accumulations of peaks of each component of the plurality of digital signals.

13 . The method of claim 12 further comprising:
generating a plurality of digital filters, each configured to compensate one of a plurality of CD candidate values;
applying at least some of the plurality of digital filters to the plurality of digital signals to produce filtered signals; and
computing a cost for each CD candidate value from the filtered signals according to cost function representing the accumulations of peaks.

14 . The method of claim 13 , wherein the plurality of digital signals comprise one or more polarization components, each comprising an in-phase (I) component and a quadrature-phase (Q) component, wherein each digital filter is applied to the I component and the Q component of each polarization component, wherein the filtered signal produced by each digital filter comprises a real component and an imaginary component, and wherein computing the costs for the CD candidate values further comprises accumulating a maximum signal peak magnitude of each of the real component and the imaginary component of each polarization component for each CD candidate value.

15 . The method of claim 13 , wherein the plurality of digital filters are frequency domain filters, and wherein the method further comprises:
performing a fast Fourier transform (FFT) to convert in-phase (I) and quadrature-phase (Q) components of each polarization component into a frequency domain prior to applying the plurality of digital filters; and performing an inverse FFT (IFFT) to convert each filtered signal into a time domain prior to computing the costs.

16 . The method of claim 13 , further comprising searching for a minimum cost value over the costs, and wherein determining the best-match CD estimate comprises setting the best-match CD estimate to a CD candidate value that produces the minimum cost value.

17 . The method of claim 12 , wherein each digital signal in the plurality of digital signals is an electrical signal.

18 . A coherent optical receiver comprising:
a front end configured to:
receive an optical signal; and
convert the optical signal into a plurality of digital signals;
one or more frequency domain equalizers (FDEQs) coupled to an output of the front end and configured to:
receive the plurality of digital signals; and
compensate chromatic dispersion (CD) in the optical signal; and
a CD estimate (CDE) unit coupled to the FDEQs and configured to deteimine a best-match CD estimate associated with the optical signal by minimizing accumulations of peaks of each component of the plurality of digital signals, wherein the FDEQs are further configured to use the best-match CD estimate to compensate the CD in the optical signal.

19 . The coherent optical receiver of claim 18 , wherein the CDE unit is further configured to configure the FDEQs with a plurality of CD candidate values, and wherein, for each CD candidate value, the CDE unit is further configured to:
compute coefficients for the FDEQs such that the FDEQs equalize a CD effect of a corresponding CD candidate value; apply the FDEQs to the plurality of digital signals to produce equalized signals; and compute a cost for the corresponding CD candidate value from the equalized signals according to cost function representing the accumulations of peaks.

20 . The coherent optical receiver of claim 19 , wherein to optimize the cost function, the CDE unit is further configured to search for a minimum cost valu

Assignees

• Futurewei Technologies Inc

Inventors

• Zamani Mahdi
• Zhang Zhuhong
• Li Chuandong

Classifications

• H04B10/613

  including phase diversity, e.g., having in-phase and quadrature branches, as in QPSK coherent receivers · CPC title

• H04B10/614

  comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers (H04J14/06 takes precedence) · CPC title

• H04B10/6161 Primary

  Compensation of chromatic dispersion · CPC title

• H04B10/612

  for optical signals modulated with a format different from binary or higher-order PSK [X-PSK], e.g. QAM, DPSK, FSK, MSK, ASK · CPC title