# US 8,542,956 B2 · Optical-fiber-compatible acoustic sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,542,956 B2 - Document ID: US8542956B2 - Status: Granted - Kind: B2 - Application number: 13/047,668 - Filed: 2011-03-14 - Published: 2011-11-03 - Granted: 2013-09-24 - Earliest claimed: 2010-03-15 - Assignees: The Board of Trustees of the Leland Stanford Junior University - Applicants: Onur Can Akkaya; Michel J. F. Digonnet; Onur Kilic; Gordon S. Kino; Olav Solgaard - Inventors: Onur Can Akkaya; Michel J. F. Digonnet; Onur Kilic; Gordon S. Kino; Olav Solgaard - Web page: https://patentgrep.com/patent/US8542956B2 ## CPC - G01H 9/004: {using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125)} - G02B 6/262: {Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements} - G02B 6/32: having lens focusing means {positioned between opposed fibre ends (with lens being an integral part of the single fibre end G02B6/262)} - G02B 2006/12138: {Sensor} - Y10T 29/49826: Assembling or joining - G01H: MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract 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. ## Claims ### Claim 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. ### Claim 2 (depends on 1) The acoustic sensor of claim 1, wherein the medium is water. ### Claim 3 (depends on 2) 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. ### Claim 4 (depends on 1) The acoustic sensor of claim 1, wherein the element within the optical cavity is a diaphragm comprising the reflective element. ### Claim 5 (depends on 4) The acoustic sensor of claim 4, wherein the element within the optical cavity is mechanically coupled to the optical fiber. ### Claim 6 (depends on 1) The acoustic sensor of claim 1, wherein at least a portion of the light reflected by the reflective element propagates into the optical fiber. ### Claim 7 (depends on 1) 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. ### Claim 8 (depends on 1) The acoustic sensor of claim 1, wherein the element within the optical cavity comprises silica. ### Claim 9 (depends on 1) The acoustic sensor of claim 1, wherein the element within the optical cavity is spaced from the reflective element. ### Claim 10 (depends on 1) The acoustic sensor of claim 1, wherein the reflective element comprises a photonic-crystal structure. ### Claim 11 (depends on 1) The acoustic sensor of claim 1, wherein the element within the optical cavity comprises a diaphragm comprising the reflective element. ### Claim 12 (depends on 11) 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. ### Claim 13 (depends on 11) 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. ### Claim 14 (depends on 13) The acoustic sensor of claim 13, wherein the optical fiber comprises fused silica and the structural element comprises fused silica. ### Claim 15 (depends on 11) 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. ### Claim 16 (depends on 11) 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. ### Claim 17 (depends on 11) The acoustic sensor of claim 11, wherein the diaphragm comprises one or more fluid conduits. ### Claim 18 (depends on 17) The acoustic sensor of claim 17, wherein the one or more fluid conduits are separate from the reflective element. ### Claim 19 (depends on 1) The acoustic sensor of claim 1, wherein the medium is a liquid. ### Claim 20 (depends on 19) The acoustic sensor of claim 19, further comprising at least one generally compressible and generally elastic element. ### Claim 21 (depends on 20) The acoustic sensor of claim 20, wherein the at least one generally compressible and generally elastic element is a gas bubble.