# US 10,320,141 B2 · Hard target detection for optical systems > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,320,141 B2 - Document ID: US10320141B2 - Status: Granted - Kind: B2 - Application number: 15/784,799 - Filed: 2017-10-16 - Published: 2019-04-18 - Granted: 2019-06-11 - Earliest claimed: 2017-10-16 - Assignees: Rosemount Aerospace Inc. - Applicants: Rosemount Aerospace Inc. - Inventors: Mark Sherwood Miller; Mark Ray - Web page: https://patentgrep.com/patent/US10320141B2 ## CPC - H01S 3/0014: {Monitoring arrangements not otherwise provided for (photometry G01J1/00, e.g. G01J1/4257; radiation pyrometry G01J5/00; measuring coherence of light G01J9/00; measuring wavelength of light G01J9/00, e.g. G01J9/0246; measuring optical pulses G01J11/00; calorimetrically measuring power of laser beams G01K17/003)} - G01S 7/481: Constructional features, e.g. arrangements of optical elements - G01S 7/4818: {using optical fibres} - G01S 7/484: Transmitters - G01S 17/04: Systems determining the presence of a target - G01S 17/08: for measuring distance only (indirect measurement G01S17/46; active triangulation systems G01S17/48) - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES ## Abstract A system and method for detecting hard targets in a free-space laser system includes a laser, an optical detector, and electronics. The laser is configured to emit a laser beam along an optical path through transmitter optics into a field of view. The optical detector is positioned along a laser transmitter path and configured to receive retroreflections of the laser beam. The electronics are configured to determine if an output of the optical detector is indicative of presence of a hard target within the field of view, and control the laser to a safe state if the output is indicative of presence of the hard target. ## Claims ### Claim 1 A hard target detection system of a free-space laser system, the hard target detection system comprising: a laser configured to emit a laser beam along an optical path through transmitter optics into a field of view; an optical detector positioned along a laser transmitter path and configured to receive retroreflections of the laser beam; electronics configured to determine if an output of the optical detector is indicative of presence of a hard target within the field of view, and control the laser to a safe state if the output is indicative of presence of the hard target; and receiver optics configured to direct backscatter of the laser beam to sensor detector elements, and wherein the optical detector is separate from the sensor detector elements. ### Claim 2 (depends on 1) The hard target detection system of claim 1, further comprising: a tap positioned along the optical path and configured to direct a portion of the laser beam to a laser monitor and a portion of the retroreflections to the optical detector. ### Claim 3 (depends on 2) The hard target detection system of claim 2, wherein the tap is a beam splitter. ### Claim 4 (depends on 1) The hard target detection system of claim 1, wherein the optical path and the transmitter optics include a first fiber optic cable, and wherein the optical detector includes a second fiber optic cable, and wherein the laser beam is directed into the field of view through a transmitter end of the first fiber optic cable, and wherein the second fiber optic cable receives the retroreflections through a detector end of the second fiber optic cable, and wherein the transmitter end is located adjacent to the detector end. ### Claim 5 (depends on 1) The hard target detection system of claim 1, wherein the electronics are configured to determine if an output of the optical detector is indicative of presence of the hard target by comparing an amplitude of the retroreflections to a threshold, and wherein the safe state is an off state of the laser. ### Claim 6 (depends on 1) The hard target detection system of claim 1, wherein the laser is configured to emit the laser beam as a pulsed laser beam, and wherein the electronics are further configured to determine if the hard target is greater than a nominal ocular hazard distance away from the transmitter optics. ### Claim 7 (depends on 1) The hard target detection system of claim 1, wherein the free-space laser system is a lidar system implemented onboard an aircraft. ### Claim 8 A method of detecting hard targets in a free-space laser system, the method comprising: emitting a laser beam along an optical path to transmitter optics; directing, by the transmitter optics, the laser beam into a field of view along a laser transmitter path; receiving, by an optical detector positioned along the laser transmitter path, retroreflections of the laser beam; detecting a hard target within the field of view based on the retroreflections; controlling the laser to a safe state if the hard target is detected within the field of view; receiving, by receiver optics, backscatter of the laser beam; directing the received backscatter to sensor detector elements; and determining properties of a volume within the field of view based upon output of the sensor detector elements. ### Claim 9 (depends on 8) The method of claim 8, further comprising: directing, by a tap positioned along the optical path, a portion of the laser beam to a laser monitor; and directing, by the tap, a portion of the retroreflections to the optical detector. ### Claim 10 (depends on 9) The method of claim 9, wherein the tap is a beam splitter. ### Claim 11 (depends on 8) The method of claim 8, wherein the optical path and the transmitter optics include a first fiber optic cable, and wherein the optical detector includes a second fiber optic cable, and wherein directing, by the transmitter optics, the laser beam into the field of view along a laser transmitter path comprises directing the laser beam into the field of view through a transmitter end of the first fiber optic cable, and wherein receiving, by the optical detector, the retroreflections of the laser beam along the transmitter path comprises receiving the retroreflections through a detector end of the second fiber optic cable, wherein the transmitter end of the first fiber optic cable is located adjacent to the detector end of the second fiber optic cable. ### Claim 12 (depends on 8) The method of claim 8, wherein detecting the hard target within the field of view based on the retroreflections comprises detecting the hard target if an amplitude of the retroreflections is greater than a threshold. ### Claim 13 (depends on 8) The method of claim 8, wherein controlling the laser to the safe state comprises turning the laser off. ### Claim 14 (depends on 8) The method of claim 8, wherein emitting the laser beam comprises emitting the laser beam as a pulsed laser beam. ### Claim 15 (depends on 14) The method of claim 14, wherein controlling the laser to the safe state if the output of the optical detector is greater than the threshold comprises detecting a hard target within the field of view if the output of the optical detector is greater than the threshold. ### Claim 16 (depends on 15) The method of claim 15, wherein controlling the laser to the safe state further comprises: determining a distance to the hard target based upon timing of the pulsed laser beam; and controlling the laser to the safe state if the hard target is within a nominal ocular hazard distance of the transmitter optics. ### Claim 17 (depends on 8) The method of claim 8, wherein the free-space laser system is a lidar system implemented onboard an aircraft. ### Claim 18 (depends on 8) The method of claim 8, wherein the optical detector is a photo-diode.