Method and Apparatus for Characterization and Compensation of Optical Impairments in InP-Based Optical Transmitter

Patent metadata

Field	Value
Publication number	US-2018198531-A1
Application number	US-201815915032-A
Country	US
Kind code	A1
Filing date	Mar 7, 2018
Priority date	Dec 19, 2015
Publication date	Jul 12, 2018
Grant date	—

Abstract

A method and apparatus for characterizing and compensating optical impairments in an optical transmitter includes operating an optical transmitter comprising a first and second parent MZ, each comprising a plurality of child MZ modulators that are biased at respective initial operating points. An electro-optic RF transfer function is generated for each of the plurality of child MZ modulators. Curve fitting parameters are determined for each of the plurality of electro-optic RF transfer functions and operating points of each child MZ modulator are determined using the curve fitting parameters. An IQ power imbalance is determined using the curve fitting parameters. Initial RF drive power levels are determined that compensate for the determined IQ power imbalance. The XY power imbalance is determined for initial RF drive power levels using the curve fitting parameters. The operating RF drive powers are determined that at least partially compensate for the first and second IQ power imbalances and for the XY power imbalance for the optical transmitter. An optical signal comprising a Nyquist-pulse-shape is generated at an output of the optical transmitter.

First claim

What is claimed is:

1 . A method for characterizing and compensating for optical impairments in an optical transmitter, the method comprising:
a) operating an optical transmitter comprising a first parent Mach-Zehnder (MZ) modulator and a second parent MZ modulator, wherein each of the first and second parent MZ modulators comprises a plurality of child MZ modulators; b) biasing each of the plurality of child MZ modulators in the first and second parent MZ modulators at respective initial operating points; c) generating an electro-optic RF transfer function for each of the plurality of child MZ modulators by measuring a plurality of optical output powers of the optical transmitter while sweeping characterizing RF input drive power levels applied to each of the plurality of child MZ modulators; d) determining curve fitting parameters for each of the plurality of electro-optic RF transfer functions; e) determining operating points of each of the plurality of child MZ modulators using the curve fitting parameters; f) determining an IQ power imbalance at a particular operating point for each of the first and the second parent MZ modulators using the curve fitting parameters for each of the plurality of electro-optic RF transfer functions; g) determining initial RF input drive power levels applied to each of the plurality of child MZ modulators that compensate for the determined IQ power imbalance for each of the first and the second parent MZ modulators; h) determining XY power imbalance of the optical transmitter at the determined initial RF input drive power levels using the curve fitting parameters; i) determining operating RF input drive power levels that at least partially compensate for the first and second IQ power imbalances and for the XY power imbalance of the optical transmitter; and j) generating an optical signal comprising a Nyquist-pulse-shape at an output of the optical transmitter.

2 . The method of characterizing and compensating of claim 1 wherein the plurality of child MZ modulators comprise InP MZ modulators.

3 . The method of characterizing and compensating of claim 1 wherein the optical transmitter operates over a range of wavelengths.

4 . The method of characterizing and compensating of claim 3 wherein the operating RF input drive power levels that at least partially compensate for the first and second IQ power imbalances and XY power imbalance of the optical transmitter are determined over the range of wavelengths.

5 . The method of characterizing and compensating of claim 1 wherein the first parent MZ modulator generates a modulated optical beam having a first polarization and the second parent MZ modulator generates a modulated optical beam having a second polarization.

6 . The method of characterizing and compensating of claim 1 wherein the biasing the plurality of child MZ modulators at the initial operating point comprises biasing the plurality of child MZ modulators at a minimum transmission level.

7 . The method of characterizing and compensating of claim 1 wherein the biasing the plurality of child MZ modulators at the initial operating point comprises biasing the plurality of child MZ modulators at a bias that results in an optical output power that is less than −45 dBm.

8 . The method of characterizing and compensating of claim 1 wherein the biasing the plurality of child MZ modulators at the initial operating point comprises biasing the plurality of child MZ modulators at a quadrature point.

9 . The method of characterizing and compensating of claim 1 wherein the characterizing RF input drive power comprises characterizing RF input drive power over a particular RF frequency that is in a range of 500 MHz to 3 GHz.

10 . The method of characterizing and compensating of claim 1 wherein the sweeping characterizing RF input drive power applied to of each of the plurality of child MZ modulators comprises sweeping the characterizing RF input drive power of each of the plurality of child MZ modulators sequentially.

11 . The method of characterizing and compensating of claim 1 wherein the sweeping characterizing RF input drive power comprises sweeping characterizing RF input drive power of each of the plurality of child MZ modulators through a respective V π of the child MZ modulators.

12 . The method of characterizing and compensating of claim 1 wherein the sweeping characterizing RF input drive power comprises varying an output power of an external RF signal generator coupled to an RF input of each of the plurality of child MZ modulators in a range of −15 dBm to +6 dBm.

13 . The method of characterizing and compensating of claim 1 wherein the particular operating point used to determine the IQ power imbalance is Vπ.

14 . The method of characterizing and compensating of claim 1 wherein the particular operating point used to determine the IQ power imbalance is between 10 dBm and 13.5 dBm.

15 . The method of characterizing and compensating of claim 1 wherein the particular operating point used to determine the IQ power imbalance is between 12 dBm and 15 dBm.

16 . The method of characterizing and compensating of claim 1 wherein the generating the electro-optic RF transfer function for each of the plurality of child MZ modulators by measuring the plurality of optical output powers of the optical transmitter while sweeping characterizing RF input drive power levels applied to each of the plurality of child MZ modulators comprises reading swept characterizing RF input drive power from an RF peak detector.

17 . The method of characterizing and compensating of claim 16 wherein the RF peak detector is calibrated by measuring the response of the RF peak detector at three or more applied input voltages.

18 . The method of characterizing and compensating of claim 1 wherein the determining curve fitting parameters for each of the plurality of electro-optic RF transfer functions comprises performing a linear curve fit.

19 . The method of characterizing and compensating of claim 1 wherein the determining curve fitting parameters for each of the plurality of electro-optic RF transfer functions comprises performing a polynomial curve fit.

20 . The method of characterizing and compensating of claim 1 wherein the determining curve fitting parameters for each of the plurality of electro-optic RF transfer functions comprises performing an inverse cosine curve fit.

21 . The method of characterizing and compensating of claim 1 further comprising determining voltage set points of modulator drive amplifiers that drive the plurality of child MZ modulators using the operating RF drive powers.

22 . The method of characterizing and compensating of claim 21 further comprising performing automatic gain control using the voltage set points of the modulator drive amplifiers to compensate power imbalances.

23 . A method of characterizing and compensating for optical impairments in an InP-based optical transmitter, the method comprising:
a) operating an optical transmitter comprising an X-Pol. IQ and a Y-Pol. IQ modulator, wherein each of the X-Pol. IQ and the Y-Pol. IQ modulators comprise a first and second child MZ modulator, over a range of wavelengths; b) biasing each of the first and second child MZ modulators in each of the X-Pol. IQ and the Y-Pol. IQ modulators at respective initial operating points; c) generating an electro-optic RF transfer function for each of the first and second child MZ mo

Assignees

• Finisar Corp

Inventors

• Bhandare Suhas P
• Ereifej Heider N
• Khalouf Ihab E
• Colyar Mark

Classifications

• H04B10/58 Primary

  Compensation for non-linear transmitter output · CPC title

• H04B10/07955

  Monitoring or measuring power · CPC title

• H04B10/588 Primary

  in external modulation systems · CPC title

• H04B10/564

  Power control · CPC title

• H04B10/516

  Details of coding or modulation · CPC title