# US 8,786,857 B2 · Mitigation of optical signal noise using a multimode transmit fiber > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,786,857 B2 - Document ID: US8786857B2 - Status: Granted - Kind: B2 - Application number: 13/389,902 - Filed: 2010-08-10 - Published: 2012-06-07 - Granted: 2014-07-22 - Earliest claimed: 2009-08-10 - Assignees: Zolo Technologies, Inc. - Applicants: Bernard Patrick Masterson; James Howell; Henrik Hofvander; Andrew D. Sappey - Inventors: Bernard Patrick Masterson; James Howell; Henrik Hofvander; Andrew D. Sappey - Web page: https://patentgrep.com/patent/US8786857B2 ## CPC - F02C 7/00: Features, components parts, details or accessories, not provided for in, or of interest apart form groups F02C1/00 - F02C6/00; Air intakes for jet-propulsion plants (controlling F02C9/00) - G01N 21/39: using tunable lasers - F23N 5/003: {using detectors sensitive to combustion gas properties (F23N5/02, F23N5/18 - F23N5/26 take precedence)} - F23N 2225/16: burner temperature - F23N 2241/20: Gas turbines - G01N 2021/4709: {Backscatter} - G01N 2201/084: Fibres for remote transmission - Y02T 50/60: Efficient propulsion technologies, e.g. for aircraft - F02C: GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS (construction of turbines F01D; jet-propulsion plants F02K; construction of compressors or fans F04; generating combustion products of high pressure or high velocity F23R; using gas turbines in compression refrigeration plants F25B11/00) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - F23N: REGULATING OR CONTROLLING COMBUSTION (control devices specially adapted for combustion apparatus in which combustion takes place in a fluidised bed of fuel or other particles F23C10/28; condition responsive controls for regulating combustion in domestic stoves with open fires for solid fuel F24B1/187) - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract An apparatus and methods for measuring combustion parameters in the measurement zone of a gas turbine engine. The measurement zone is defined as being between an outer casing and an engine component having a reflecting surface inside the outer casing. The apparatus comprises a laser generating a transmitting beam of light of a select wavelength and a multimode transmitting fiber optically coupled to the laser. A transmitting optic is optically coupled to the multimode optical fiber for transmitting the beam into the measurement zone. The reflecting surface is configured to provide a Lambertian reflection. A receiving optic is positioned to receive the Lambertian reflection. Means are provided in operative association with the multimode transmitting fiber for averaging modal noise induced signal level variation of light propagating within the multimode transmitting fiber. ## Claims ### Claim 1 An apparatus for measuring a combustion parameter in a zone, the apparatus comprising: a laser generating a transmit beam of light of a select wavelength; a multimode transmitting optical fiber optically coupled to the laser; a transmitting optic optically coupled to the multimode transmitting optical fiber for transmitting the transmit beam into the zone; a reflecting surface in the zone; a receiving optic positioned to receive a reflection of the transmit beam from the reflecting surface; wherein the transmitting optic and the receiving optic are the same optic; and means operatively associated with the multimode transmitting optical fiber for averaging modal noise induced signal level variation of light propagating within the multimode transmitting optical fiber. ### Claim 2 (depends on 1) The apparatus of claim 1 wherein the multimode transmitting optical fiber also functions as a receiving optical fiber. ### Claim 3 (depends on 2) The apparatus of claim 2 further comprising means optically coupled to the multimode transmitting optical fiber for separating the received beam from the transmitting beam. ### Claim 4 (depends on 3) The apparatus of claim 3 wherein the means for separating comprises one of a spatial multiplexer and a circulator. ### Claim 5 (depends on 1) The apparatus of claim 1 further comprising the reflecting surface being configured to provide a Lambertian reflection. ### Claim 6 (depends on 1) The apparatus of claim 1 wherein the means for averaging comprises one of: means for cyclically varying an index of refraction of the multimode optical fiber over a select period of time; and means for scrambling a light distribution within the multimode optical fiber. ### Claim 7 (depends on 1) The apparatus of claim 1 wherein the means for averaging comprises an apparatus configured to perform at least one of: cyclically varying the temperature of the multimode optical fiber; twisting the multimode optical fiber; stretching the multimode optical fiber; shaking the multimode optical fiber; and vibrating the multimode optical fiber. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the zone is a measurement zone of a gas turbine engine, the measurement zone being defined as being between an outer casing of the engine and an engine component having a reflecting surface inside the outer casing. ### Claim 9 An apparatus for measuring a combustion parameter in a zone, the apparatus comprising: a laser generating a transmit beam of light of a select wavelength; a multimode optical fiber optically coupled to the laser; a transmitting/receiving optic optically coupled to multimode optical fiber; and a reflecting surface in the zone, the reflecting surface being constructed and arranged to reflect at least a portion of the transmit beam transmitted from the transmitting/receiving optic back to the transmitting/receiving optic; wherein the multimode optical fiber carries both the transmit beam and the at least a portion of the transmitted beam reflected back to the transmitting/receiving optic; and wherein the transmitting/receiving optic is configured to transmit the transmit beam into the zone, and receive the at least a portion of the transmitted beam reflected from the reflecting surface. ### Claim 10 (depends on 9) The apparatus of claim 9 further comprising means optically coupled to the multimode optical fiber for separating the at least a portion of the transmitted beam reflected back to the transmitting/receiving optic from the transmit beam. ### Claim 11 (depends on 10) The apparatus of claim 10 wherein the means for separating comprises one of a spatial multiplexer and a circulator. ### Claim 12 (depends on 9) The apparatus of claim 9 further comprising the reflecting surface being configured to provide a Lambertian reflection. ### Claim 13 (depends on 9) The apparatus of claim 9 further comprising means operatively associated with the multimode optical fiber for averaging modal noise induced signal level variation of light propagating within the multimode optical fiber. ### Claim 14 A method of measuring a property within a zone, the method comprising: transmitting a beam of light of a select wavelength through a multimode optical fiber and a transmit optic optically coupled to the zone; reflecting at a reflecting surface at least a portion of the transmitted beam to a receiving optic; receiving from the reflecting surface a reflection of the at least a portion of the transmitted beam with the receiving optic optically coupled to the transmit optic; the transmitting optic and the receiving optic being the same optic; and averaging modal noise induced signal level variations of the beam of light propagating within the multimode optical fiber. ### Claim 15 (depends on 14) The method of claim 14 further comprising the multimode optical fiber carrying the transmitted beam and the at least a portion of the received beam. ### Claim 16 (depends on 15) The method of claim 15 further comprising separating the at least a portion of the received beam from the transmitted beam. ### Claim 17 (depends on 16) The method of claim 16 further comprising detecting the strength of the at least a portion of the received beam. ### Claim 18 (depends on 14) The method of claim 14 wherein the step of averaging modal noise is performed by cyclically manipulating the multimode optical fiber. ### Claim 19 (depends on 14) The method of claim 14 further comprising reflecting the transmitted beam off a surface in the zone to the receiving optic. ### Claim 20 (depends on 19) The method of claim 19 further comprising providing a Lambertian dispersion of the transmitted beam at the surface in the zone.