Optical synthesizer tuning using fine and coarse optical frequency combs

Patent metadata

Field	Value
Publication number	US-9407373-B2
Application number	US-201414549374-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 synthesizer including a coarse optical frequency comb, a fine optical frequency comb, and an output laser. The coarse comb is pumped with a first pump laser, and an absolute frequency of at least one tooth of the coarse optical frequency comb is set. The fine comb is pumped with a second pump laser and has a frequency spacing between teeth that is locked to a fractional or integer multiple of a radio frequency reference. Initially, the second pump laser is locked to a first tooth of the coarse optical frequency comb. The optical frequency synthesizer can be tuned by sweeping the second pump laser and locking the second pump laser to a desired tooth. An output signal can then be generated with the output laser based on a tooth of fine comb after the second pump is locked to the desired tooth.

First claim

What is claimed is:

1. An optical frequency synthesizer comprising:
a coarse optical frequency comb pumped with a first pump laser, wherein an absolute frequency of at least one tooth of the coarse optical frequency comb is set;
a fine optical frequency comb having a frequency spacing between teeth that is locked to a fractional or integer multiple of a radio frequency reference, the fine optical frequency comb pumped with a second pump laser, wherein the second pump laser is initially locked to a first tooth of the coarse optical frequency comb; and
an output laser;
wherein the optical frequency synthesizer is configured to:
sweep the second pump laser to near a desired tooth of the coarse optical frequency comb;
lock the second pump laser to the desired tooth; and
generate an output signal with the output laser based on a tooth of fine optical frequency comb after the second pump laser is locked to the desired tooth.

2. The optical frequency synthesizer of claim 1 , wherein the optical frequency synthesizer is configured to repeat the sweep and lock of the second pump laser for each tooth between the first tooth and the desired tooth to incrementally step the second pump laser from the first tooth to the desired tooth.

3. The optical frequency synthesizer of claim 1 , wherein sweep the second pump laser includes sweep the second pump laser from the first tooth, and while sweeping the second pump laser, count any teeth of the coarse optical frequency comb that the second pump laser passes, and determine that the second pump laser is near the desired tooth based on the number of teeth that have been passed during the sweep.

4. The optical frequency synthesizer of claim 3 , wherein count any teeth includes identify any teeth by detecting a resulting beat note from a mixing of the fine optical frequency comb with the coarse optical frequency comb.

5. The optical frequency synthesizer of claim 4 , wherein the optical frequency synthesizer is configured to turn off sidebands of the fine optical frequency comb during the mixing.

6. The optical frequency synthesizer of claim 1 , wherein a third tooth of the coarse optical frequency comb is initially locked to a fourth tooth of the fine optical frequency comb with a servo loop such that the fine optical frequency comb and the coarse optical frequency comb are mutually-referenced, wherein the optical frequency synthesizer is configured to:
sample and hold the servo loop prior to the sweep and lock of the second pump laser to the desired tooth; and
after the lock of the second pump laser to the desired tooth, re-lock a fifth tooth of the coarse optical frequency comb to the fourth tooth of the fine optical frequency comb, wherein the fifth tooth is an equal number of teeth away from the desired tooth as the third tooth is away from the first tooth.

7. The optical frequency synthesizer of claim 6 , wherein the optical frequency synthesizer is configured to:
repeat the sample and hold, sweep and lock of the second pump laser for each tooth between the first tooth and the desired tooth to incrementally step the second pump laser from the first tooth to the desired tooth; and
after each respective lock of the second pump laser to each respective tooth between the first tooth and the desired tooth, re-lock a tooth of the coarse optical frequency comb to the fourth tooth of the fine optical frequency comb, wherein the tooth of the coarse optical frequency comb is a tooth that is an equal number of teeth away from the respective tooth to which the second pump laser is locked as the third tooth is away from the first tooth.

8. The optical frequency synthesizer of claim 6 , 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 a coarse optical frequency comb corresponds to the third tooth being aligned with the fourth tooth.

9. The optical frequency synthesizer of claim 1 , wherein a frequency spacing of the coarse optical frequency comb is at least 10 times larger than a frequency spacing of the fine optical frequency comb.

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

11. The optical frequency synthesizer 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.

12. A method of tuning an optical frequency synthesizer, the method comprising:
providing a coarse optical frequency comb pumped with a first pump laser, wherein an absolute frequency of at least one tooth of the coarse optical frequency comb is set;
providing a fine optical frequency comb having a frequency spacing between teeth that is locked to a fractional or integer multiple of a radio frequency reference, the fine optical frequency comb pumped with a second pump laser, wherein the second pump laser is initially locked to a first tooth of the coarse optical frequency comb;
sweeping the second pump laser to near a desired tooth of the coarse optical frequency comb;
locking the second pump laser to the desired tooth; and
generating an output signal based on a tooth of fine optical frequency comb after the second pump laser is locked to the desired tooth.

13. The method of claim 12 , comprising:
repeating the sweeping and locking of the second pump laser for each tooth between the first tooth and the desired tooth to incrementally step the second pump laser from the first tooth to the desired tooth.

14. The method of claim 12 , wherein sweeping the second pump laser includes sweeping the second pump laser from the first tooth, and while sweeping the second pump laser, counting any teeth of the coarse optical frequency comb that the second pump laser passes, and determining that the second pump laser is near the desired tooth based on the number of teeth that have been passed during the sweeping.

15. The method of claim 14 , wherein counting any teeth includes identifying any teeth by detecting a resulting beat note from a mixing of the fine optical frequency comb with the coarse optical frequency comb.

16. The method of claim 15 , comprising turning off sidebands of the fine optical frequency comb during the mixing.

17. The method of claim 12 , wherein a third tooth of the coarse optical frequency comb is initially locked to a fourth tooth of the fine optical frequency comb with a servo loop such that the fine optical frequency comb and the coarse optical frequency comb are mutually-referenced, the method comprising:
sampling and holding the servo loop prior to the sweep and lock of the second pump laser to the desired tooth; and
after locking the second pump laser to the desired tooth, re-locking a fifth tooth of the coarse optical frequency comb to the fourth tooth of the fine optical frequency comb, wherein the fifth tooth is an equal number of teeth away from the desired tooth as the third tooth is away from the first tooth.

18. The method of claim 17 , comprising:
repeating the sampling and holding, sweeping and locking of the second pump laser for each tooth between the first tooth and the desired tooth to incrementally step the second pump laser from the first tooth to the desired tooth; and
after each respective lock of the second pump to each respective tooth between the first tooth and the desired tooth, re-locking a tooth of the coarse optical frequency comb to the fourth tooth of the fine optical

Assignees

• Honeywell Int Inc

Inventors

• Fertig Chad
• Tin Steven

Classifications

• G02F2/02 Primary

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

• H01S3/1303

  by using a passive reference, e.g. absorption cell (H01S3/139 takes precedence) · CPC title

• H04B10/503 Primary

  Laser transmitters · CPC title

• H01S3/10084

  Frequency control by seeding · CPC title

• H04B10/508

  Pulse generation, e.g. generation of solitons · CPC title