Mutually-referenced optical frequency combs

Patent metadata

Field	Value
Publication number	US-9407060-B2
Application number	US-201414549359-A
Country	US
Kind code	B2
Filing date	Nov 20, 2014
Priority date	May 7, 2014
Publication date	Aug 2, 2016
Grant date	Aug 2, 2016

Abstract

Embodiments herein provide for an optical frequency reference including a fine optical frequency comb and a coarse optical frequency comb. The fine comb has a first tooth and a frequency spacing (FCS) between teeth that is locked to a fractional or integer multiple of a radio frequency reference. The coarse comb has a second tooth that is locked to the first tooth and a frequency spacing (CCS) between teeth that is locked to an integer multiple of the FCS. An absolute optical frequency of at least one tooth of the coarse optical frequency comb is set.

First claim

What is claimed is:

1. An optical frequency reference comprising:
a first micro-resonator and a second micro-resonator; and
at least one pump laser configured to:
pump the first micro-resonator to generate a fine optical frequency comb having a first tooth and a frequency spacing (FCS) between teeth that is locked to a fractional or integer multiple of a radio frequency reference; and
pump the second micro-resonator to generate a coarse optical frequency comb having a second tooth that is locked to the first tooth and a frequency spacing (CCS) between teeth that is locked to an integer multiple of the FCS, wherein an absolute optical frequency of at least one tooth of the coarse optical frequency comb is set.

2. The optical frequency reference of claim 1 , wherein the CCS is at least 10 times larger than the FCS.

3. The optical frequency reference of claim 1 , wherein the fine optical frequency comb does not span an octave.

4. The optical frequency reference of claim 1 , wherein the CCS is locked to an integer multiple of FCS by locking a third tooth of the coarse optical frequency comb to a fourth tooth of the fine optical frequency comb.

5. The optical frequency reference of claim 4 , wherein the third tooth is an adjacent tooth to the second tooth such that the third tooth is separated from the second tooth by the CCS.

6. The optical frequency reference of claim 4 , wherein the third tooth is locked to the fourth tooth by setting a free spectral range (FSR) of a resonator for the coarse optical frequency comb such that a beat frequency between a mixing of the fine optical frequency comb and the coarse optical frequency comb corresponds to the third tooth being aligned with the fourth tooth.

7. The optical frequency reference of claim 1 , wherein the radio frequency reference is derived from one of parametric seeding of a resonator or a closed loop servo control of a resonator.

8. The optical frequency reference of claim 1 , wherein the second tooth is locked to the first tooth by one of using a common pump laser to pump the fine optical frequency comb and the coarse optical frequency comb or by using a first pump laser for the fine optical frequency comb and a second pump laser for the coarse optical frequency comb, wherein the first pump laser and the second pump laser are locked to one another.

9. The optical frequency reference of claim 1 , wherein the absolute optical frequency of the at least one tooth is set by one of self-heterodyned interferometry or by referencing the at least one tooth to a sufficiently stable laser.

10. A method for mutually-referencing two optical frequency combs, the method comprising:
generating a fine optical frequency comb by pumping a first micro-resonator with at least one pump laser;
generating a coarse optical frequency comb by pumping a first micro-resonator with at least one pump laser;
locking a first tooth of the fine optical frequency comb to a second tooth of the coarse optical frequency comb;
locking a frequency spacing of the fine optical frequency comb to a fractional or integer multiple of a radio frequency reference;
locking a frequency spacing of the coarse optical frequency comb to an integer multiple of the frequency spacing of the fine optical frequency comb; and
setting a frequency offset of the coarse optical frequency comb.

11. The method claim 10 , wherein locking the frequency spacing of the coarse optical frequency comb to an integer multiple of the frequency spacing of the fine optical frequency comb includes locking a third tooth of the coarse optical frequency comb to a fourth tooth of the fine optical frequency comb.

12. The method of claim 11 , wherein the third tooth is an adjacent tooth to the second tooth such that the third tooth is separated from the second tooth by the frequency spacing of the coarse optical frequency comb.

13. The method of claim 11 , wherein locking the third tooth to the fourth tooth includes setting a free spectral range (FSR) of a resonator for the coarse optical frequency comb such that a beat frequency between an output of the fine optical frequency comb and an output of the coarse optical frequency comb corresponds to the third tooth being aligned with the fourth tooth.

14. The method of claim 10 , wherein the radio frequency reference is derived from one of parametric seeding of a resonator or a closed loop servo control of a resonator.

15. The method of claim 10 , wherein locking the first tooth to the second tooth includes one of: pumping the fine optical frequency comb and the coarse optical frequency comb with a common pump laser, or pumping the fine optical frequency comb with a first pump laser and pumping the coarse optical frequency comb with a second pump laser and locking the first pump laser to the second pump laser.

16. The method of claim 10 , wherein the frequency spacing of the coarse optical frequency comb is at least 10 times larger than the frequency spacing of the fine optical frequency comb.

17. The method of claim 10 , wherein the fine optical frequency comb does not span an octave.

18. The method claim 10 , wherein setting the frequency offset includes one of self-referencing two teeth of the coarse optical frequency comb or referencing at least one tooth of the coarse optical frequency comb to a sufficiently stable laser.

19. An optical synthesizer, comprising:
a fine optical frequency comb having a first tooth and a second tooth and a frequency spacing (FCS) between teeth that is locked to a fractional or integer multiple of a radio frequency reference; and
a coarse optical frequency comb having a third tooth and a fourth tooth, wherein the third tooth is locked to the first tooth and the fourth tooth is locked to the second tooth,
wherein a frequency offset for the coarse optical frequency comb and the fine optical frequency comb is set by self-referencing two teeth of the coarse optical frequency comb;
an output laser; and
a direct digital synthesizer (DDS) operating in the microwave band, the DDS configured to:
detect a difference in frequency between a selected tooth of the fine optical frequency comb and the output laser; and
adjust the output laser based on the detected difference to set the output laser to a desired frequency.

20. The optical synthesizer of claim 19 , wherein the fourth tooth is an adjacent tooth to the third tooth such that the fourth tooth is separated from the third tooth by a frequency spacing of the coarse optical frequency comb,
wherein the fourth tooth is locked to the second tooth by setting a free spectral range (FSR) of a resonator for the coarse optical frequency comb such that a beat frequency between an output of the fine optical frequency comb and an output of the coarse optical frequency comb corresponds to the fourth tooth being aligned with the second tooth,
wherein the third tooth is locked to the first tooth by one of using a common pump laser to pump the fine optical frequency comb and the coarse optical frequency comb or by using a first pump laser for the fine optical frequency comb and a second pump laser for the coarse optical frequency comb, wherein the first pump laser and the second pump laser are locked to one another.

Assignees

• Honeywell Int Inc

Inventors

• Fertig Chad
• Tin Steven

Classifications

• G02F2203/56

  Frequency comb synthesizer · CPC title

• H04B10/506

  Multiwavelength transmitters · CPC title

• G02F2/02 Primary

  Frequency-changing of light, e.g. by quantum counters · CPC title

• H01S3/13 Primary

  Stabilisation of laser output parameters, e.g. frequency or amplitude · CPC title

• G01B9/02008

  by using a frequency comb · CPC title