Optical-fiber-compatible acoustic sensor
An acoustic sensor includes a diaphragm having a reflective element. The sensor has an optical fiber positioned relative to the reflective element such that light emitted from the optical fiber is reflected by the reflective element. A first end of the optical fiber and the reflective element form an optical cavity therebetween. The acoustic sensor further includes a structural element mechanically coupled to the diaphragm and the optical fiber. The structural element includes a material having a coefficient of thermal expansion substantially similar to the coefficient of thermal expansion of the optical fiber. For example, the material can be silica.
1. An acoustic sensor comprising:
a reflective element;
an optical fiber positioned relative to the reflective element such that light emitted from the optical fiber is reflected by the reflective element, wherein a first end of the optical fiber and the reflective element form an optical cavity therebetween, the optical cavity comprising a medium having a refractive index change with temperature; and
an element within the optical cavity having a coefficient of thermal expansion and thickness that compensate the refractive index change with temperature.
2. The acoustic sensor of claim 1 , wherein the medium is water.
3. The acoustic sensor of claim 2 , wherein the element within the optical cavity comprises silica and has a thickness approximately equal to a distance between the first end of the optical fiber and the reflective element.
4. The acoustic sensor of claim 1 , wherein the element within the optical cavity is a diaphragm comprising the reflective element.
5. The acoustic sensor of claim 4 , wherein the element within the optical cavity is mechanically coupled to the optical fiber.
6. The acoustic sensor of claim 1 , wherein at least a portion of the light reflected by the reflective element propagates into the optical fiber.
7. The acoustic sensor of claim 1 , wherein the first end of the optical fiber comprises a second reflective element, the second reflective element and the reflective element forming a Fabry-Perot cavity therebetween.
8. The acoustic sensor of claim 1 , wherein the element within the optical cavity comprises silica.
9. The acoustic sensor of claim 1 , wherein the element within the optical cavity is spaced from the reflective element.
10. The acoustic sensor of claim 1 , wherein the reflective element comprises a photonic-crystal structure.
11. The acoustic sensor of claim 1 , wherein the element within the optical cavity comprises a diaphragm comprising the reflective element.
12. The acoustic sensor of claim 11 , wherein the diaphragm comprises silica having a thickness approximately equal to a distance between the first end of the optical fiber and the diaphragm.
13. The acoustic sensor of claim 11 , further comprising a structural element mechanically coupling the reflective element and the optical fiber, wherein the structural element comprises silica.
14. The acoustic sensor of claim 13 , wherein the optical fiber comprises fused silica and the structural element comprises fused silica.
15. The acoustic sensor of claim 11 , wherein the diaphragm has a lateral dimension and a ratio of the lateral dimension to the optical fiber diameter is in a range between 1.2 and 8.
16. The acoustic sensor of claim 11 , wherein the diaphragm has a movable portion having an area and a ratio of the area to a cross-sectional area of the optical fiber is in a range between 1.4 and 64.
17. The acoustic sensor of claim 11 , wherein the diaphragm comprises one or more fluid conduits.
18. The acoustic sensor of claim 17 , wherein the one or more fluid conduits are separate from the reflective element.
19. The acoustic sensor of claim 1 , wherein the medium is a liquid.
20. The acoustic sensor of claim 19 , further comprising at least one generally compressible and generally elastic element.
21. The acoustic sensor of claim 20 , wherein the at least one generally compressible and generally elastic element is a gas bubble.