Method using asymmetric optical resonances

1. A method of detecting acoustic waves, the method comprising:

providing an acoustic sensor comprising:

an optical resonator having an optical resonance with a resonance lineshape that is asymmetric as a function of wavelength, wherein the resonance lineshape has a minimum reflectivity at a resonance wavelength, a first side with wavelengths below the resonance wavelength, and a second side with wavelengths above the resonance wavelength, the second side less steep than the first side; and

a housing substantially surrounding at least a portion of the optical resonator and mechanically coupled to the optical resonator, wherein the optical resonance is responsive to acoustic waves incident upon the housing;

exposing the acoustic sensor to acoustic waves; and

detecting a change of the optical resonance induced by the acoustic waves, wherein said detecting comprises irradiating the optical resonator with a first light signal having a first wavelength on the first side of the resonance lineshape and irradiating the optical resonator with a second light signal having a second wavelength on the second side of the resonance lineshape.

2. The method of claim 1 , wherein the optical resonator comprises a reflective element and a spatial mode filter positioned relative to the reflective element such that light emitted from the spatial mode filter is reflected by the reflective element.

3. The method of claim 2 , wherein the spatial mode filter comprises a single-mode optical fiber.

4. The method of claim 2 , wherein the spatial mode filter comprises an optically transmissive portion and an optically non-transmissive portion which bounds at least a portion of the optically transmissive portion.

5. The method of claim 4 , wherein the optically transmissive portion is a hole through the optically non-transmissive portion.

6. The method of claim 2 , wherein the reflective element comprises a portion of a photonic crystal structure.

7. The method of claim 6 , wherein the photonic crystal structure comprises at least one photonic crystal slab.

8. The method of claim 6 , wherein the photonic crystal structure comprises a pair of photonic crystal slabs substantially parallel to one another.

9. The method of claim 2 , wherein the spatial mode filter comprises an optical fiber with a first end that is partially reflective and partially transmissive to light emitted by the optical fiber, the first end of the optical fiber and the reflective element forming a Fabry-Perot optical resonator having a cavity therebetween.

10. The method of claim 9 , wherein the cavity comprises a gas.

11. The method of claim 9 , wherein the cavity comprises a liquid.

12. The method of claim 2 , wherein the spatial mode filter comprises an optical fiber with a fiber Bragg grating, wherein the fiber Bragg grating and the reflective element form a Fabry-Perot optical resonator.

13. The method of claim 2 , wherein at least a portion of the light reflected by the reflective element is transmitted through the spatial mode filter.

14. The method of claim 1 , wherein irradiating the optical resonator with the first light signal and irradiating the optical resonator with the second light signal occur concurrently.

15. The method of claim 1 , wherein irradiating the optical resonator with the first light signal and irradiating the optical resonator with the second light signal occur sequentially.

16. The method of claim 15 , wherein irradiating the optical resonator with the first light signal occurs before irradiating the optical resonator with the second light signal.

17. The method of claim 2 , wherein the reflective element comprises a dielectric mirror.

18. The method of claim 2 , wherein the reflective element comprises a metallic mirror surface.

19. The method of claim 2 , wherein the spatial mode filter comprises a metal layer.

20. The method of claim 2 , wherein the spatial mode filter comprises a dielectric mirror.