Apparatus and methods for digital signal constellation transformation

Patent metadata

Field	Value
Publication number	US-10038505-B2
Application number	US-201715820304-A
Country	US
Kind code	B2
Filing date	Nov 21, 2017
Priority date	Apr 16, 2015
Publication date	Jul 31, 2018
Grant date	Jul 31, 2018

Abstract

Apparatus and method for digital signal constellation transformation are provided herein. In certain configurations, an integrated circuit includes an analog front-end that converts an analog signal vector representing an optical signal into a digital signal vector, and a digital signal processing circuit that processes the digital signal vector to recover data from the optical signal. The digital signal processing circuit generates signal data representing a signal constellation of the digital signal vector. The digital signal processing circuit includes an adaptive gain equalizer that compensates the signal data for distortion of the signal constellation arising from biasing errors of optical modulators used to transmit the optical signal.

First claim

What is claimed is:

1. A method of operating an integrated optical module, the method comprising:
receiving, by a coherent optical receiver, an optical signal from an optical cable of the integrated optical module;
generating, by the coherent optical receiver, an analog signal representing the optical signal;
processing, by a transceiver, the analog vector to generate a digital signal vector, wherein the digital signal vector comprises a digital representation of an in-phase (I) component and a quadrature-phase (Q) component of the optical signal; and
generating, by the transceiver, signal data representing a signal constellation of the digital signal vector;
wherein generating the signal data comprises
generating, by an adaptive gain equalizer of the transceiver, transformed signal data by compensating the signal data for distortion of the signal constellation,
generating, by the adaptive gain equalizer, an estimate of an angular tilt of the signal constellation, and
compensating, by the adaptive gain equalizer, the signal data based on the estimate of the angular tilt.

2. The method of claim 1 wherein generating the estimate of the angular tilt comprises generating, by the adaptive gain equalizer, the angular tilt based on a sum of a plurality of cross-correlations of I and Q components of the signal constellation.

3. The method of claim 2 wherein the sum of the plurality of cross-correlations is computed over a moving window of data samples obtained from the digital signal vector.

4. The method of claim 1 wherein generating the estimate of the angular tilt further comprises iteratively revising, by the adaptive gain equalizer, the estimate of the angular tilt until I and Q components of the transformed signal data are substantially uncorrelated.

5. The method of claim 4 wherein iteratively revising the estimate of the angular tilt comprises iteratively revising, by the adaptive gain equalizer, the estimate of the angular tilt based on a step gain, wherein the step gain changes based on a number of times the angular tilt has been estimated.

6. The method of claim 1 wherein generating the transformed signal data comprises generating, by the adaptive gain equalizer, the transformed signal data based on a transformation matrix that includes the estimate of the angular tilt.

7. The method of claim 6 wherein the transformation matrix is about equal to

1

cos
2

⁢
θ

-

sin
2

⁢
θ

⁡

[

cos
⁢

⁢
θ

-
sin

⁢

⁢
θ

-
sin

⁢

⁢
θ

cos
⁢

⁢
θ

]

,

wherein θ is the estimate of the angular tilt.

8. The method of claim 1 further comprising processing, by the digital signal processing circuit, the signal data for at least one of feed forward equalization or carrier recovery prior to compensating the signal data for distortion of the signal constellation.

9. The method of claim 1 further comprising slicing, by a decision slicer, the transformed signal data.

10. The method of claim 1 wherein the distortion of the signal constellation comprises at least one of squeezing, shifting, or tilting.

11. The method of claim 1 wherein the optical signal comprises a multi-level quadrature amplitude modulation (QAM) signal, a discrete multi-toned (DMT) modulation signal, an orthogonal frequency division multiplexing (OFDM), or a phase-shift keying (PSK) signal.

12. The method of claim 1 wherein the digital signal vector comprises data representing a single polarization modulation or a dual-polarization modulation.

13. A method of operating an integrated optical module, the method comprising:
receiving, by a coherent optical receiver, an optical signal from an optical cable of the integrated optical module;
generating, by the coherent optical receiver, an analog signal vector representing the optical signal;
processing, by a transceiver, the analog signal vector to generate a digital signal vector, wherein the digital signal vector comprises a digital representation of an in-phase (I) component and a quadrature-phase (Q) component of the optical signal; and
generating, by the transceiver, signal data representing a signal constellation of the digital signal vector;
wherein generating the signal data comprises
generating, by an adaptive gain equalizer of the transceiver, transformed signal data by compensating the signal data for distortion of the signal constellation,
compensating, by the adaptive gain equalizer, for distortion for a first portion of the signal data associated with a horizontal polarization of the optical signal, and
compensating, by the adaptive gain equalizer, for distortion for a second portion of the signal data associated with a vertical polarization of the optical signal.

14. The method of claim 13 wherein generating the transformed signal data comprises generating, by the adaptive gain equalizer, the transformed signal data based on a transformation matrix that includes the estimate of the angular tilt.

15. The method of claim 14 wherein the transformation matrix is about equal to

1

cos
2

⁢
θ

-

sin

Assignees

• Inphi Corp

Inventors

• Fan Shu Hao

Classifications

• H04B10/613

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

• H04B10/5057

  using a feedback signal generated by analysing the optical output · CPC title

• H04B10/6165

  Estimation of the phase of the received optical signal, phase error estimation or phase error correction · CPC title

• H04B10/40 Primary

  Transceivers · CPC title

• H04B2210/252

  after the transmission line, i.e. post-compensation · CPC title