Coherent dual parametric frequency comb for ultrafast chromatic dispersion measurement in an optical transmission link

• US 9,625,351 B2
• Filed: 03/05/2014
• Issued: 04/18/2017
• Est. Priority Date: 03/05/2013
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Ataie, Vahid, Kuo, Ping Piu, Radic, Stojan
• Primary Examiner(s): Lapage, Michael P
• Application Number:
  US14/198,581
• Publication Number:
  US 20140253915A1
• Time in Patent Office: 1,140 Days
• CPC Class Codes: G01M 11/333 using modulated input signals
• CPC Class Codes: G01M 11/338 by measuring dispersion other than PMD, e.g. chromatic dispersion
• CPC Class Codes: G01N 21/41 Refractivity; Phase-affecting properties, e.g. optical path length G01N21/21 takes precedence
• CPC Class Codes: H04B 10/07951 Monitoring or measuring chromatic dispersion or PMD

Abstract

A wide-band optical frequency comb is provided to estimate an optical phase shift induced in a dispersive material. In contrast to the conventional techniques that rely on a single tunable laser for extracting the dispersion parameter at different frequencies, the wide-band optical frequency comb uses multiple comb lines for simultaneously evaluating the dispersion induced phase shifts in different frequencies. Since the frequency response of the dispersive material is a phase function, a phase associated with each comb line passed through the material represents a discrete measure of the material frequency response.

Claims

1. A method for evaluating an optical transmission link for spreading of an optical signal across a length of the link, comprising:

measuring the optical transmission link for the presence of chromatic dispersion across the length of the link using a wide-band optical frequency comb having a plurality of comb lines to estimate optical phase shifts simultaneously at a plurality of different frequencies;

wherein measuring the optical transmission link further comprises mapping the estimated optical phase shift of each received comb line to a corresponding comb line of an electrical signal separated by a frequency-spacing mismatch;

setting the minimum required capturing time for measuring the optical transmission link to a single period of lowest harmonic of the reference comb; and

estimating the chromatic dispersion in a single cycle of frequency-spacing mismatch.

2. The method of claim 1, wherein the wide-band optical frequency comb is a dual-phase locked optical frequency comb comprising a probe comb and a reference comb, wherein the probe comb and the reference comb have difference frequency offset spacings.

3. The method of claim 1, wherein the wide-band optical frequency comb comprises more than 10 lines.

4. The method of claim 1, wherein the wide-band optical frequency comb comprises approximately 100 lines with a spacing of approximately 1 nanometer (nm).

5. The method of claim 4, further comprising measuring for the presence of chromatic dispersion in 1 millisecond (ms) when an electrical receiver bandwidth is 1 gigahertz (GHz) and a laser linewidth is 100 kilohertz (kHz).

6. A system for measurement of chromatic dispersion, comprising:

a laser source;

an optical fiber span;

a dual-phase locked optical frequency comb disposed at a first end of the optical fiber span and configured for receiving an optical signal from the laser source and generating an input into the first end of the optical fiber span, the input comprising a plurality of comb lines at a plurality of different frequencies for simultaneous transmission over the optical fiber span;

a detector disposed at a second end of the optical fiber span, the detector configured for simultaneously receiving and converting received optical comb lines transmitted across a length of the optical fiber span into electrical comb lines; and

a processor for determining a phase shift in each of the electrical comb lines;

wherein the processor determines the phase shift by mapping an estimated optical phase shift of each comb line to a corresponding electrical comb line separated by a frequency-spacing mismatch;

wherein the processor sets the minimum required capture time for measuring the optical transmission link to a single period of lowest harmonic of the reference comb; and

wherein the processor estimates the chromatic dispersion in a single cycle of frequency-spacing mismatch.

7. The system of claim 6, wherein the dual-phase locked optical frequency comb comprises a probe comb and a reference comb, and wherein the probe comb and the reference comb have difference frequency offset spacings.

8. The system of claim 6, wherein the dual-phase locked optical frequency comb comprises more than 10 lines.

9. The system of claim 6, wherein the dual-phase locked optical frequency comb comprises approximately 100 lines with a spacing of approximately 1 nanometer (nm).

10. The system of claim 9, wherein a minimum required capturing time for measurement of the presence of chromatic dispersion is 1 millisecond (ms) with an electrical receiver bandwidth of 1 gigahertz (GHz) and a laser linewidth of 100 kilohertz (kHz).

11. The system of claim 6, wherein the plurality of comb lines are configured to estimate optical phase shifts at different frequencies at the same time.

12. A method for optimizing an optical transmission link, comprising:

evaluating an optical transmission link for upgrading to higher data rate transmission by measuring chromatic dispersion within the optical transmission link using an optical frequency comb having from 10 to 100 comb lines to estimate optical shifts simultaneously at a plurality of different frequencies;

wherein the wide-band optical frequency comb is a dual-phase locked optical frequency comb comprising a probe comb and a reference comb, wherein the probe comb and the reference comb have difference frequency offset spacings;

setting the minimum required capturing time for measuring the optical transmission link to a single period of lowest harmonic of the reference comb; and

estimating the chromatic dispersion in a single cycle of frequency-spacing mismatch.

13. The method of claim 12, wherein the wide-band optical frequency comb comprises approximately 100 lines with a spacing of approximately 1 nanometer (nm).