Apparatus and method for measurement of optical frequency shifts

Patent metadata

Field	Value
Publication number	US-10488259-B2
Application number	US-201515317963-A
Country	US
Kind code	B2
Filing date	Jun 10, 2015
Priority date	Jun 12, 2014
Publication date	Nov 26, 2019
Grant date	Nov 26, 2019

Abstract

An apparatus and method for measuring small changes in the centroid of the spectrum of a light field by conversion of optical frequency centroid shifts into time delays are described. A time delay for a particular frequency of light is created by directing the light into an optically dispersive system that converts the change in center frequency to a change in transit time through the system as the dispersive element causes different colors to travel at different speeds. Examples of such dispersive elements include, but are not limited to, optical fibers, bulk materials, volumetric or fiber Bragg gratings, and grating or prism based pulse stretchers. This time delay can be measured, by detecting the change in transit time (or time of flight through the dispersive element) by using a detector such as a photodiode, PMT, etc. that converts the incident optical pulse train into an electronic pulsed signal. The phase of the periodic electronic signal provides a measure of the timing delay of the pulse, and can be determined by adapting standard methods of electronic oscillator phase detection relative to a reference electronic oscillator clock.

First claim

What is claimed is:

1. A method for measuring a shift in a center optical frequency of light from a light source, from that of a known center optical frequency, the method comprising:
directing the light, having a shifted center optical frequency, into an optically dispersive system, whereby the light having the shifted center optical frequency experiences a first transit time through the dispersive system;
measuring the first transit time;
directing control light having the known center optical frequency into the optically dispersive system, whereby the control light having the known center optical frequency experiences a second transit time through the dispersive system;
measuring the second transit time;
generating a time delay from a difference of the first transit time and the second transit time; and
determining the shift in the center optical frequency based on the time delay.

2. The method of claim 1 , wherein the optically dispersive system is chosen from optical fibers, bulk materials, volumetric or fiber Bragg gratings, and grating or prism based pulse stretchers.

3. The method of claim 1 , wherein the light source generates optical pulses, each pulse having a center optical frequency.

4. The method of claim 3 , wherein said step of measuring the first transit time comprises converting the optical pulses into periodic electronic pulsed signals, and measuring the phase of the periodic electronic pulsed signals relative to a reference electronic oscillator clock, whereby the time delays of the pulses are determined.

5. The method of claim 3 , wherein said step of measuring the second transit time and comprises converting the optical pulses into periodic electronic pulsed signals, and measuring the phase of the periodic pulsed signals relative to a reference electronic oscillator clock, whereby the time delays of the pulses are determined.

6. The method of claim 4 or 5 , wherein the time delay is measured using a method chosen from Optical Phase-Locked Loop, intensity cross correlation, and direct pulse train measurement.

7. The method of claim 4 or 5 , wherein said step of converting the optical pulses into periodic electronic pulsed signals is achieved by directing the optical pulses onto a photodetector.

8. The method of claim 4 or 5 , wherein said step of measuring the phase of the periodic pulsed signals is achieved using electronic oscillator phase detection.

9. An apparatus for measuring a shift in a center optical frequency of light from a light source, from that of a known center optical frequency, the apparatus comprising:
an optically dispersive system for receiving light from said light source, whereby light having a shifted center optical frequency travels through said dispersive system in a first time period, different from a second time period for control light having the known center optical frequency to travel through said dispersive system; and
means for measuring the first time period;
whereby a difference between the first time period and the second time period is determined and is indicative of the shift of the center optical frequency relative to the known center optical frequency.

10. The apparatus of claim 9 , wherein said optically dispersive system is chosen from optical fibers, bulk materials, volumetric or fiber Bragg gratings, and grating or prism based pulse stretchers.

11. The apparatus of claim 9 , wherein said light source generates optical pulses, each pulse having a center optical frequency.

12. The apparatus of claim 11 , further comprising at least one photodetector wherein the optical pulses are converted into periodic electronic pulses.

13. The apparatus of claim 12 , wherein said means for measuring the first time period comprises means for measuring the phase of the periodic electronic pulses.

14. The apparatus of claim 13 , wherein said phase measurement means comprises apparatus for electronic oscillator phase detection.

15. The apparatus of claim 11 , wherein said means for measuring the first time period comprises an Optical Phase-Locked Loop apparatus.

16. The apparatus of claim 11 , wherein said means for measuring the first time period comprises apparatus for direct pulse train measurement.

17. A method comprising:
directing first light having a first center optical frequency into an optically dispersive system, whereby the first light having the first center optical frequency experiences a first transit time through the dispersive system;
measuring the first transit time;
determining a time delay between the first transit time and a second transit time corresponding to second light having a second center optical frequency; and
based on the time delay, determining a difference between the first center optical frequency and the second center optical frequency.

18. The method of claim 17 , further comprising the steps of:
directing the second light having the second center optical frequency into the optically dispersive system, whereby the second light having the second center frequency experiences the second transit time through the dispersive system; and
measuring the second transit time.

19. The method of claim 17 , wherein the optically dispersive system is chosen from optical fibers, bulk materials, volumetric or fiber Bragg gratings, and grating or prism based pulse stretchers.

20. The method of claim 17 , wherein the first light is generated by a light source and wherein the light source generates optical pulses, each pulse having a center optical frequency.

21. The method of claim 20 , wherein said step of measuring the first transit time comprises converting the optical pulses into periodic electronic pulsed signals, and measuring the phase of the periodic electronic pulsed signals relative to a reference electronic oscillator clock, whereby the time delays of the pulses are determined.

22. The method of claim 18 , wherein the first light is generated by a light source and wherein the light source generates optical pulses, each pulse having a center optical frequency and said step of measuring the second transit time comprises converting the optical pulses into periodic electronic pulsed signals, and measuring the phase of the periodic pulsed signals relative to a reference electronic oscillator clock, whereby the time delays of the pulses are determined.

23. The method of claims 21 or 22 , wherein the time delay is measured using a method chosen from Optical Phase-Locked Loop, intensity cross correlation, and direct pulse train measurement.

24. The method of claim 21 or 22 , wherein said step of converting the optical pulses into periodic electronic pulsed signals is achieved by directing the optical pulses onto a photodetector.

25. The method of claim 21 or 22 , wherein said step of measuring the phase of the periodic pulsed signals is achieved using electronic oscillator phase detection.

Assignees

• Univ Colorado State Res Found

Inventors

• Bartels Randy A
• Winters David G

Classifications

• G01J3/44 Primary

  Raman spectrometry; Scattering spectrometry {; Fluorescence spectrometry} · CPC title

• G02B26/001

  based on interference in an adjustable optical cavity (interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26) · CPC title

• G01N2021/653

  Coherent methods [CARS] · CPC title

• G01J3/26

  using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters · CPC title

• G01J3/433

  Modulation spectrometry; Derivative spectrometry · CPC title