Method and apparatus for reducing interference in an optical data stream using data-independent equalization

• US 6,956,917 B2
• Filed: 04/17/2003
• Issued: 10/18/2005
• Est. Priority Date: 04/17/2003
• Status: Expired due to Term

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Finisar Corporation (II-VI Incorporated)
• Inventors: Lenosky, Thomas J.
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US10/419,023
• Publication Number:
  US 20040208266A1
• Time in Patent Office: 915 Days
• Field of Search: 375/232, 375/346, 375/350, 375/234, 375/229, 375/340, 375/355, 375/285, 708/303, 708/300, 708/322, 708/323, 359/161.189
• US Class Current: 375/350
• CPC Class Codes: H04B 10/2543 due to fibre non-linearities, e.g. Kerr effect

Abstract

An optoelectronic assembly for reducing interference in an optical data stream received over a channel includes a converter, an equalizer, a microcontroller, and a comparator. The converter converts the optical data stream to an electrical signal. The equalizer, including a set of filter coefficients, filters the electrical data stream and generates a filtered signal. The comparator compares the filtered signal against a threshold value to generate a set of data values. The microcontroller includes: logic for generating one or more correlation statistics, where each correlation statistic reduces data components of the electrical signal; logic for estimating a channel response reflecting dispersion in the channel, based at least in part on the one or more correlation statistics; logic for determining the set of filter coefficients for the equalizer; and logic for adaptively updating the set of filter coefficients to reflect time-varying changes in the channel response.

Claims

1. A method for reducing interference in an optical data stream received over a channel, the method comprising:

receiving an electrical signal derived from the optical data stream;

computing a plurality of time-correlation statistics from the electrical signal that reduce data components of the electrical signal;

estimating, at least in part from the plurality of time-correlation statistics, a channel response that contains dispersion information for the channel;

calculating, at least in part from the channel response, a set of filter coefficients for an adaptive equalizer;

filtering the electrical signal using the set of filter coefficients to create a filtered signal; and

comparing the filtered signal to a threshold value to generate a plurality of data values for the optical data stream.

2. The method of claim 1, wherein the computing, estimating, and calculating are repeated in order to adaptively update the set of filter coefficients of the adaptive equalizer.

3. The method of claim 1, wherein the calculated set of filter coefficients are an initial set of coefficients, and wherein the adaptive equalizer converges using the initial set of coefficients without requiring a training sequence.

4. The method of claim 1, wherein the step of estimating the channel response is conducted by using the plurality of time-correlation statistics to determine spacing between, and amplitudes of, a plurality of modeled channel-response peaks.

5. The method of claim 1, wherein the step of estimating the channel response comprises:

modeling the plurality of time-correlation statistics using a plurality of expansion coefficients;

comparing the computed time-correlation statistics with the modeled time-correlation statistics;

iteratively optimizing the expansion coefficients; and

using the expansion coefficients to estimate the channel response.

6. The method of claim 1, wherein the set of filter coefficients further includes a set of precursor filter coefficients and a set of postcursor filter coefficients.

7. The method of claim 6, wherein the step of calculating further includes:

computing a vector of channel response samples based at least in part on the estimated channel response;

computing a time-correlation matrix based at least in part on the estimated channel response;

determining an optimal set of the precursor filter coefficients through a function that includes at least the vector of channel response samples and the time correlation matrix; and

determining an optimal set of the postcursor coefficients through a function that includes at least the optimal set of the precursor filter coefficients and the estimated channel response.

8. The method of claim 1, wherein the calculating step includes determining a set of filter coefficients that reduces channel dispersion by optimizing portions of the estimated channel response.

9. The method of claim 1, further comprising:

determining a data clock of the electrical signal based at least in part on the filtered signal.

10. An optoelectronic assembly for reducing interference in an optical data stream received over a channel, the optoelectronic assembly comprising:

a converter to convert the optical data stream to an electrical signal;

an equalizer to filter the electrical data stream and to generate a filtered signal, the equalizer having a set of filter coefficients;

a microcontroller comprising;

logic for generating one or more correlation statistics for the electrical signal, each correlation statistic reducing data components of the electrical signal;

logic for estimating a channel response reflecting dispersion in the channel, the estimated channel response being based at least in part on the one or more correlation statistics;

logic for determining the set of filter coefficients for the equalizer;

based at least in part on the estimated channel response; and

logic for adaptively updating the set of filter coefficients for the equalizer to reflect time-varying changes in the channel response; and

a comparator to compare the filtered signal against a threshold value to generate a plurality of data values for the optical data stream.

11. The optoelectronic assembly of claim 10, wherein the equalizer is an infinite impulse response (IIR) equalizer.

12. The optoelectronic assembly of claim 11, wherein the equalizer includes a minimum mean squared error (MMSE) filter.

13. The optoelectronic assembly of claim 10, wherein the equalizer does not require a training sequence to converge.

14. The optoelectronic assembly of claim 10, wherein the logic for estimating a channel response uses the plurality of time-correlation statistics to determine spacing between, and amplitudes of, a plurality of modeled channel-response peaks.

15. The optoelectronic assembly of claim 10, wherein the logic for estimating a channel response further comprises:

logic for modeling the plurality of time-correlation statistics using a plurality of expansion coefficients;

logic for comparing the computed time-correlation statistics with the modeled time-correlation statistics;

logic for iteratively optimizing the expansion coefficients; and

logic for using the expansion coefficients to estimate the channel response.

16. The optoelectronic assembly of claim 10, wherein the set of filter coefficients further includes a set of precursor filter coefficients and a set of postcursor filter coefficients.

17. The optoelectronic assembly of claim 16, wherein the logic for determining the set of filter coefficients further includes:

logic for computing a vector of channel response samples based at least in part on the estimated channel response;

logic for computing a time-correlation matrix based at least in part on the estimated channel response;

logic for determining an optimal set of the precursor filter coefficients through a function that includes at least the vector of channel response samples and the time-correlation matrix; and

logic for determining an optimal set of the postcursor coefficients through a function that includes at least the optimal set of the precursor filter coefficients and the estimated channel response.

18. The optoelectronic assembly of claim 10, wherein the logic for determining the set of filter coefficients further determines a set of filter coefficients that reduces channel dispersion by minimizing portions of the estimated channel response.

19. The optoelectronic assembly of claim 10, further comprising:

a data clock recovery circuit for determining a data clock of the electrical signal based at least in part on the filtered signal.