# US 5,349,437 A · Electromagnetic radiation detector utilizing an electromagnetic radiation absorbing element in a Mach-Zehnder interferometer arrangement > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,349,437 A - Document ID: US5349437A - Status: Granted - Kind: A - Application number: 07/954,521 - Filed: 1992-09-30 - Granted: 1994-09-20 - Earliest claimed: 1992-09-30 - Assignees: The United States of America as represented by the Secretary of the Navy - Inventors: Lloyd C. Bobb - Web page: https://patentgrep.com/patent/US5349437A ## CPC - G01J 5/58: using absorption; using extinction effect - G01J 9/02: by interferometric methods (using interferometers for measuring optically the linear dimensions of objects G01B9/02) - G01J 2009/023: {of the integrated optical type} - G01J 2009/0288: {Machzehnder} - G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N) ## Abstract Apparatus is provided to detect electromagnetic radiation, in which a radion-absorbing element is disposed on a short section of an optical waveguide to provide a thermal interface therebetween. Radiation is absorbed by the element, which thereby heats the waveguide, causing it to change its optical pathlength in proportion to the radiation absorbed. Interferometer apparatus is connected to measure this change in optical pathlength as a change in the interference condition. This device is highly sensitive and can be operated at room temperature. ## Claims ### Claim 1 Apparatus for detecting electromagnetic radiation, comprising: a single-mode optical waveguide; an electromagnetic radiation-absorbing element disposed at a thermal interface with said waveguide along a longitudinal portion of the length thereof to apply heat thereto in proportion to the magnitude of electromagnetic radiation impinged upon and absorbed by said electromagnetic radiation-absorbing element; means for chopping the electromagnetic radiation impinged upon said electromagnetic radiation-absorbing element; and interferometer apparatus operatively connected to said waveguide to measure a change in the optical pathlength thereof in proportion to the heat applied thereto, which change in optical pathlength is indicative of the amount of electromagnetic radiation absorbed. ### Claim 2 (depends on 1) The apparatus of claim 1, further comprising means for shielding the length of said waveguide not having said electromagnetic radiation-absorbing element disposed thereon. ### Claim 3 (depends on 1) The apparatus of claim 1 wherein the thickness of said electromagnetic radiation-absorbing element is determined in accordance with the desired sensitivity of the apparatus. ### Claim 4 (depends on 1) The apparatus of claim 1 wherein said electromagnetic radiation-absorbing element circumferentially encloses a longitudinal segment of said waveguide. ### Claim 5 (depends on 1) The apparatus of claim 1, further comprising: means for collecting the electromagnetic radiation and focussing it onto said electromagnetic radiation-absorbing element; and means adjacent to said electromagnetic radiation-absorbing element for filtering unwanted preselected wavelengths of electromagnetic radiation from impinging upon said electromagnetic radiation-absorbing element. ### Claim 6 (depends on 5) The apparatus of claim 5, wherein said electromagnetic radiation-absorbing element is carbon. ### Claim 7 Apparatus for detecting electromagnetic radiation, comprising: a single-mode optical waveguide; an electromagnetic radiation-absorbing element disposed at a thermal interface with said waveguide along a longitudinal portion of the length thereof to apply heat thereto in proportion to the magnitude of electromagnetic radiation impinged upon and absorbed by said electromagnetic radiation-absorbing element; means for collecting the electromagnetic radiation and focussing it onto said electromagnetic radiation-absorbing element; and interferometer apparatus operatively connected to said waveguide to measure a change in the optical pathlength thereof in proportion to the heat applied thereto, which change in optical pathlength is indicative of the amount of electromagnetic radiation absorbed. ### Claim 8 (depends on 7) The apparatus of claim 7, wherein said collecting and focussing means is a lens positioned adjacent to said electromagnetic radiation-absorbing element. ### Claim 9 (depends on 7) The apparatus of claim 7, wherein said single-mode optical waveguide is etched along the longitudinal portion of the length thereof having said electromagnetic radiation-absorbing element disposed thereon. ### Claim 10 Apparatus for detecting electromagnetic radiation, comprising: a single-mode optical waveguide; an electromagnetic radiation-absorbing element disposed at a thermal interface with said waveguide along a longitudinal portion of the length thereof to apply heat thereto in proportion to the magnitude of electromagnetic radiation impinged upon and absorbed by said electromagnetic radiation-absorbing element; a means adjacent to said electromagnetic radiation-absorbing element for filtering unwanted preselected wavelengths of electromagnetic radiation from impinging upon said electromagnetic radiation-absorbing element; and interferometer apparatus operatively connected to said waveguide to measure a change in the optical pathlength thereof in proportion to the heat applied thereto, which change in optical pathlength is indicative of the amount of electromagnetic radiation absorbed. ### Claim 11 Apparatus for detecting electromagnetic radiation, comprising: a single-mode optical waveguide; a carbon element disposed at a thermal interface with said waveguide along a longitudinal portion of the length thereof to apply heat thereto in proportion to the magnitude of electromagnetic radiation impinged upon and absorbed by said carbon element; and interferometer apparatus operatively connected to said waveguide to measure a change in the optical pathlength thereof in proportion to the heat applied thereto, which change in optical pathlength is indicative of the amount of electromagnetic radiation absorbed.