# US 2009/0260501 A1 · Multi-mode optical fiber sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2009/0260501 A1 - Document ID: US20090260501A1 - Status: Published application - Kind: A1 - Application number: 12/426,746 - Filed: 2009-04-20 - Published: 2009-10-22 - Earliest claimed: 2008-04-18 - Inventors: Raman KASHYAP - Web page: https://patentgrep.com/patent/US20090260501A1 ## 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)} - G01D 5/35345: {using Amplitude variations to detect the measured quantity} - G01K 11/32: using changes in transmittance, scattering or luminescence in optical fibres - G01L 1/242: {the material being an optical fibre} - G01H: MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES - G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR - G01K: MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR (radiation pyrometry G01J5/00) - G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G) ## Abstract There is described an optical fiber sensor for sensing one of vibration, temperature, and strain, comprising: a laser source; a first single mode optical fiber having a first end and a second end, the first end connected to the laser source for receiving and propagating light from the laser source; a multimode optical fiber having a first end and a second end, the first end connected to the second end of the first single mode optical fiber for receiving the light and thereby exciting a plurality of modes of the multimode optical fiber, the multimode optical fiber being stretched at an out of band frequency and operated at a point at which an output is a linear function of a displacement of the multimode fiber; and a sampling photo-detector module connected to the second end of the multimode optical fiber for spatially filtering an output of the multimode fiber to obtain a spatially filtered interference pattern, and for detecting a variation of the spatially filtered interference pattern when one of the vibration, temperature, and strain is applied to the multimode optical fiber. ## Claims ### Claim 1 An optical fiber sensor for sensing one of vibration, temperature, and strain, comprising: a laser source; a first single mode optical fiber having a first end and a second end, the first end connected to the laser source for receiving and propagating light from the laser source; a multimode optical fiber having a first end and a second end, the first end connected to the second end of the first single mode optical fiber for receiving said light and thereby exciting a plurality of modes of said multimode optical fiber, the multimode optical fiber being stretched at an out of band frequency and operated at a point at which an output is a linear function of a displacement of the multimode fiber; and a sampling photo-detector module connected to the second end of the multimode optical fiber for spatially filtering an output of said multimode fiber to obtain a spatially filtered interference pattern, and for detecting a variation of said spatially filtered interference pattern when one of said vibration, temperature, and strain is applied to said multimode optical fiber. ### Claim 2 (depends on 1) The sensor of claim 1, wherein the sampling photo-detector module comprises a second single mode optical fiber for said spatially filtering and a photodiode for said detecting. ### Claim 3 (depends on 1) The sensor of claim 1, wherein the sampling photo-detector module comprises a small area photodiode for sampling and detecting. ### Claim 4 (depends on 1) The sensor of claim 1, further comprising a control mechanism to return the sensor to an operating point once the multimode optical fiber is stretched. ### Claim 5 (depends on 4) The sensor of claim 4, wherein the control mechanism is a multimode control fiber in series with the multimode optical fiber. ### Claim 6 (depends on 1) The sensor of claim 1, wherein the multimode optical fiber comprises a plurality of segments, each one of said segments having a distinct resonance frequency. ### Claim 7 (depends on 1) The sensor of claim 1, wherein the sensor is a musical instrument, and said multimode optical fiber represents a string of said musical instrument. ### Claim 8 (depends on 6) The sensor of claim 6, wherein said sensor is a guitar, and the multimode optical fiber represents all strings of said guitar and is jacketed multiple times in a peg box with a tuning peg for each one of said segments. ### Claim 9 (depends on 6) The sensor of claim 6, wherein each one of the segments is independently tensioned. ### Claim 10 (depends on 9) The sensor of claim 9, wherein the segments are of varying lengths. ### Claim 11 (depends on 1) The sensor of claim 1, wherein the multimode optical fiber is coated with a material. ### Claim 12 (depends on 1) The sensor of claim 1, further comprising an amplifier for amplifying an output signal. ### Claim 13 A method for sensing one of vibration, temperature, and strain, the method comprising: stretching a multimode optical fiber at an out of band frequency such that it operate at a point at which an output is a linear function of a displacement of the multimode optical fiber; powering a laser source coupled to a first end of a first single mode optical fiber; propagating light through said first single mode optical fiber, a second end of said first single mode optical fiber being coupled to a first end of the multimode optical fiber; exciting a plurality of modes in said multimode optical fiber by coupling said light propagating through said first single mode optical fiber into said multimode optical fiber; spatially filtering an output of said multimode fiber to obtain an interference pattern; and detecting a variation of said interference pattern when one of said vibration, temperature, and strain is applied to said multimode optical fiber. ### Claim 14 (depends on 13) The method of claim 13, wherein said spatially filtering comprises receiving an output of said multimode optical fiber into a second single mode optical fiber and transmitting an output of said second single mode optical fiber to a photo-detector. ### Claim 15 (depends on 13) The method of claim 13, further comprising returning the sensor to an operating point once the multimode optical fiber is stretched using a control mechanism. ### Claim 16 (depends on 13) The method of claim 13, wherein said detecting comprises detecting a variation of said interference pattern from one of a plurality of segments of said multimode optical fiber, each one of said segments having a distinct resonance frequency. ### Claim 17 (depends on 13) The method of claim 13, further comprising producing a musical tone from said variation of said interference pattern. ### Claim 18 (depends on 17) The method of claim 17, wherein said producing a musical tone comprises producing a different musical tone from different segments of said multimode optical fiber, each one of said segments having a distinct resonance frequency. ### Claim 19 (depends on 13) The method of claim 13, further comprising amplifying an output signal. ### Claim 20 A musical instrument comprising: a housing having a neck and a body; a plurality of tuning pegs at one end of said neck; a bridge on the body; and a multimode fiber having a plurality of segments stretched at an out of band frequency and operated at a point at which an output is a linear function of a displacement of the multimode fiber, each one of said segments extending from one of said tuning pegs to the bridge, the bridge holding the multimode fiber in place on the body, the multimode optical fiber being wrapped around each one of the tuning pegs, the tuning pegs adjustable for tensioning each of the segments of the multimode optical fiber.