On-chip optical reference cavity exhibiting reduced resonance center frequency fluctuations

• US 8,848,760 B2
• Filed: 03/15/2013
• Issued: 09/30/2014
• Est. Priority Date: 06/06/2012
• Status: Active Grant

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Vahala, Kerry, Chen, Tong, Lee, Hansuek, Suh, Myoung-Gyun
• Primary Examiner(s): NGUYEN, TUAN N
• Application Number:
  US13/831,692
• Publication Number:
  US 20140105232A1
• Time in Patent Office: 564 Days
• Field of Search: 372/9, 372/39, 385/129
• US Class Current: 372/92
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02B 6/2934 Fibre ring resonators, e.g. fibre coils
• CPC Class Codes: H01S 3/0014 Monitoring arrangements not otherwise provided for photometry G01J1/00, e.g. G01J1/4257; radiation pyrometry G01J5/00; measuring coherence of light G01J9/00; measuring wavelength of light G01J9/00, e.g. G01J9/0246; measuring optical pulses G01J11/00; calorimetrically measuring power of laser beams G01K17/003
• CPC Class Codes: H01S 3/08013 Resonator comprising a fibre, e.g. for modifying dispersion or repetition rate the active medium being a fibre H01S3/067
• CPC Class Codes: H01S 3/1305 Feedback control systems
• CPC Class Codes: H01S 5/026 Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers stabilisation of output H01S5/06
• CPC Class Codes: H01S 5/0687 Stabilising the frequency of the laser

Abstract

An optical apparatus comprises a waveguide substrate and an optical reference cavity. The optical reference cavity comprises an optical waveguide formed on the waveguide substrate and arranged to form a closed loop greater than or about equal to 10 cm in length. The RMS resonance frequency fluctuation is less than or about equal to 100 Hz. The Q-factor can be greater than or about equal to 10⁸. The optical waveguide can exhibit optical loss less than or about equal to 0.2 dB/m for propagation of an optical signal along the optical waveguide. The closed loop path can comprise two or more linked spirals greater than or about equal to 1 meter in length and can occupy an area on the waveguide substrate less than or about equal to 5 cm².

Claims

1. An optical apparatus comprising:

(a) a waveguide substrate; and

(b) an optical reference cavity that (i) exhibits multiple resonance frequencies over an operational wavelength range and (ii) can be characterized over the operational wavelength range by a Q-factor and a RMS resonance frequency fluctuation,

wherein;

(c) the optical reference cavity comprises an optical waveguide formed on the waveguide substrate and arranged to form a closed loop greater than or about equal to 10 cm in length; and

(d) the RMS resonance frequency fluctuation is less than or about equal to 100 Hz.

2. The optical apparatus of claim 1 wherein:

(c′

) the optical reference cavity comprises an optical waveguide formed on the waveguide substrate and arranged to form a closed loop greater than or about equal to 2 meters in length;

(d′

) the RMS resonance frequency fluctuation is less than or about equal to 20 Hz;

or

(e′

) the Q-factor is greater than or about equal to 2×

10⁸.

3. The optical apparatus of claim 1 wherein:

(c′

) the optical reference cavity comprises an optical waveguide formed on the waveguide substrate and arranged to form a closed loop greater than or about equal to 10 meters in length;

(d′

) the RMS resonance frequency fluctuation is less than or about equal to 10 Hz;

or

(e′

) the Q-factor is greater than or about equal to 5×

10⁸.

4. The optical apparatus of claim 1 wherein the Q-factor is greater than or about equal to 10⁸.

5. The optical apparatus of claim 1 wherein the optical reference cavity comprises an optical waveguide formed on the waveguide substrate and arranged to form a closed loop greater than or about equal to 1 meter in length.

6. The optical apparatus of claim 5 wherein the optical waveguide exhibits optical loss less than or about equal to 0.2 dB/m for propagation of an optical signal along the optical waveguide.

7. The optical apparatus of claim 5 wherein the closed loop path comprises two or more linked spirals and occupies an area on the waveguide substrate less than or about equal to 5 cm².

8. The optical apparatus of claim 7 wherein at least a portion of one or more of the spirals comprises an Archimedean spiral.

9. The optical apparatus of claim 1 wherein a transverse cross section of the optical waveguide comprises a dielectric material supported by pedestal of substrate material, wherein a lateral portion of the dielectric material extends transversely beyond the pedestal of the substrate material and an optical mode of the optical reference cavity is guided at least partly by an interface between the low dielectric material and an ambient medium at a lateral surface of the extended portion of the dielectric material.

10. The optical apparatus of claim 9 wherein the lateral surface of the dielectric material forms an acute angle with a bottom surface thereof.

11. The optical apparatus of claim 9 wherein the ambient medium is gaseous and comprises atmospheric or conditioned air, one or more inert gases, or near vacuum.

12. The optical apparatus of claim 9 wherein the substrate comprises one or more semiconductor materials and the dielectric material comprises one or more oxide materials.

13. The optical apparatus of claim 9 wherein the dielectric material comprises silica or doped silica between about 2 μ

m and about 10 μ

m thick, the substrate material comprises silicon or doped silicon, and the dielectric material extends transversely more than about 70 μ

m beyond the pedestal of the substrate material.

14. The optical apparatus of claim 9 wherein the optical waveguide exhibits optical loss less than or about equal to 0.2 dB/m for propagation of the optical mode along the optical waveguide.

15. The optical apparatus of claim 1 further comprising (i) a laser source and (ii) a second optical waveguide that is arranged so as to couple optically a portion of an optical signal emitted by the laser source to the optical reference cavity.

16. The optical apparatus of claim 15 wherein the optical reference cavity and the second optical waveguide form a portion of a feedback mechanism arranged so as to lock an optical frequency of the optical signal to one of the resonance frequencies of the optical reference cavity.

17. The optical apparatus of claim 15 wherein the second optical waveguide is formed on the waveguide substrate.

18. The optical apparatus of claim 17 wherein the laser source is formed on the waveguide substrate.

19. A method employing the optical reference cavity of claim 1, the method comprising:

(i) operating a laser source to produce an output optical signal;

(ii) coupling a portion of the output optical signal to the optical reference cavity;

(iii) generating an error signal based on the interaction of the coupled portion of the optical signal with the optical reference cavity; and

(iv) controlling one or more operating parameters of the laser source based on the error signal so as to lock an optical frequency of the optical signal to one of the resonance frequencies of the optical reference cavity.

20. The method of claim 19 wherein a second optical waveguide couples the portion of the optical signal to the optical reference cavity.

21. The method of claim 20 wherein the second optical waveguide is formed on the waveguide substrate.

22. The method of claim 21 wherein the laser source is formed on the waveguide substrate.