# US 10,371,570 B2 · Burnout protection for optical sensors > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,371,570 B2 - Document ID: US10371570B2 - Status: Granted - Kind: B2 - Application number: 15/420,438 - Filed: 2017-01-31 - Published: 2018-08-02 - Granted: 2019-08-06 - Earliest claimed: 2017-01-31 - Assignees: Raytheon Company - Applicants: Raytheon Company - Inventors: Catherine Trent; Gary A. Frazier - Web page: https://patentgrep.com/patent/US10371570B2 ## CPC - G01J 1/0492: {using at least two different filters} - G01J 1/0238: {making use of sensor-related data, e.g. for identification of sensor or optical parts} - G01J 1/0448: {Adjustable, e.g. focussing} - G01J 1/22: using a variable element in the light-path, e.g. filter, polarising means (G01J1/34 takes precedence) - G01J 1/4257: {applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam (monitoring arrangements for lasers in general H01S3/0014)} - G02B 1/005: {made of photonic crystals or photonic band gap materials (photonic band-gap structures or photonic lattices in integrated optics G02B6/1225; photonic band-gap structures or photonic lattices in optical fibres G02B6/02295)} - G02B 5/281: {designed for the infrared light} - G02F 1/015: based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction (G02F1/03 takes precedence) - G02F 1/218: {using semi-conducting materials} - G01J 2001/0285: {against laser damage} - G02F 2203/055: wavelength filtering - 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) - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS ## Abstract A method and apparatus for protecting an optical sensor is disclosed. A fixed filter having a fixed passband for light transmission is placed in front of the optical sensor. A programmable filter having a variable passband for light transmission is placed in front of the fixed filter. A controllable voltage source controls a voltage at the programmable filter that shifts the passband of the programmable filter from a first state in which the passband of the programmable filter is substantially the same as the passband of the fixed filter and a second state in which the passband of the programmable filter is different than the passband of the fixed filter. ## Claims ### Claim 1 An apparatus for protecting an optical sensor, comprising: a fixed filter having a fixed passband for light transmission; a programmable filter having a variable passband for light transmission, the programmable filter including at least two quarter wavelength layers, the first quarter wavelength layer including alternating n-type layers and p-type layers of a first material and the second quarter wavelength layer including alternating n-type layers and p-type layers of a second material; and a controllable voltage source that shifts the passband of the programmable filter from a first state in which the passband of the programmable filter is substantially the same as the passband of the fixed filter and a second state in which the passband of the programmable filter is different than the passband of the fixed filter. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the fixed filter and programmable filter are located in front of an aperture of the sensor. ### Claim 3 (depends on 1) The apparatus of claim 1, further including a control device that controls the voltage source based on a measured intensity of light. ### Claim 4 (depends on 3) The apparatus of claim 3, wherein the control device controls the voltage source to apply the voltage bias when the measured intensity is greater than a threshold intensity value. ### Claim 5 (depends on 3) The apparatus of claim 3, wherein the control device includes a control sensor for receiving light from over a broad area. ### Claim 6 (depends on 3) The apparatus of claim 3, further comprising a beam splitter for redirecting a portion of light directed at the optical sensor toward the control device. ### Claim 7 (depends on 3) The apparatus of claim 3, wherein the control device includes the optical sensor. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the programmable filter includes at least one bilayer that includes a layer of n-type semiconducting material and a layer of p-type semiconducting material. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein the programmable filter includes a half-wavelength central layer having a plurality of quarter wavelength bilayers stacked above the central layer and a plurality of quarter wavelength bilayers stacked below the central layer. ### Claim 10 (depends on 1) The apparatus of claim 1, wherein the programmable filter includes a photonic crystal. ### Claim 11 A method of protecting an optical sensor, comprising: placing a fixed filter having a fixed passband for light transmission in front of the optical sensor; placing a programmable filter having a variable passband for light transmission in front of the fixed filter, the programmable filter including at least two quarter wavelength layers, the first quarter wavelength layer including alternating n-type layers and p-type layers of a first material and the second quarter wavelength layer including alternating n-type layers and p-type layers of a second material; and controlling a voltage at the programmable filter to shift the variable passband of the programmable filter with respect to the fixed passband. ### Claim 12 (depends on 11) The method of claim 11, wherein the controllable voltage source places the programmable filter in one of a first state in which the passband of the programmable filter is substantially the same as the fixed passband and a second state in which the passband of the programmable filter is different than the fixed passband. ### Claim 13 (depends on 11) The method of claim 11, further including controlling the voltage source based on an intensity of light received at a control device. ### Claim 14 (depends on 13) The method of claim 13, further comprising controlling the voltage using control device that compares a received intensity level of light to an intensity threshold value. ### Claim 15 (depends on 13) The method of claim 13, further comprising redirecting a portion of light directed at the sensor toward the control device using a beam splitter. ### Claim 16 (depends on 13) The method of claim 13, controlling the programmable filter using an intensity of light received at the sensor. ### Claim 17 (depends on 11) The method of claim 11, wherein the fixed central wavelength is about 1.55 micrometers. ### Claim 18 (depends on 11) The method of claim 11, wherein the programmable filter includes at least one bilayer that includes a layer of n-type semiconducting material and a layer of p-type semiconducting material. ### Claim 19 (depends on 18) The method of claim 18, wherein the programmable filter includes a half-wavelength central layer having a plurality of quarter wavelength bilayers stacked above the central layer and a plurality of quarter wavelength bilayers stacked below the central layer. ### Claim 20 (depends on 11) The method of claim 11, wherein the programmable filter includes a photonic crystal that includes n-type semiconductor bars arranged in a p-type matrix, further comprising electrically biasing the n-type semiconductor bars to change an optical bandgap of the photonic crystal.