# US 10,310,201 B2 · Back-reflection protection and monitoring in fiber and fiber-delivered lasers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,310,201 B2 - Document ID: US10310201B2 - Status: Granted - Kind: B2 - Application number: 14/816,211 - Filed: 2015-08-03 - Published: 2018-03-01 - Granted: 2019-06-04 - Earliest claimed: 2014-08-01 - Assignees: nLIGHT, Inc. - Applicants: nLIGHT Photonics Corporation - Inventors: Dahv A. V. Kliner - Web page: https://patentgrep.com/patent/US10310201B2 ## CPC - G02B 6/4296: {coupling with sources of high radiant energy, e.g. high power lasers, high temperature light sources} - H01S 3/0064: {Anti-reflection devices, e.g. optical isolaters (absorbing layers for marking or protecting purposes in laser working B23K26/50; magneto-optical non-reciprocal devices G02F1/093, G02F1/0955)} - H01S 3/094007: {Cladding pumping, i.e. pump light propagating in a clad surrounding the active core} - G02B 6/14: Mode converters - G02B 26/103: {having movable or deformable optical fibres, light guides or waveguides as scanning elements (light guides per se G02B6/00)} - G02B 2006/4297: {having protection means, e.g. protecting humans against accidental exposure to harmful laser radiation} - 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)} - H01S 3/005: {Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping (shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B)} - H01S 3/067: Fibre lasers - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - 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 ## Abstract A system includes an optical fiber situated to propagate a laser beam received from a laser source to an output of the optical fiber, a first cladding light stripper optically coupled to the optical fiber and situated to extract at least a portion of forward-propagating cladding light in the optical fiber, and a second cladding light stripper optically coupled to the optical fiber between the first cladding light stripper and the optical fiber output and situated to extract at least a portion of backward-propagating cladding light in the optical fiber. ## Claims ### Claim 1 A system, comprising: an optical fiber situated to propagate a laser beam received from a laser source to an output of the optical fiber; a beam directing optical system situated to receive the laser beam from the output of the optical fiber; the beam directing optical system including an output beam combiner situated to combine the received laser beam with one or more other laser beams; a first cladding light stripper optically coupled to the optical fiber and situated to extract at least a portion of forward-propagating cladding light in the optical fiber; and a second cladding light stripper optically coupled to the optical fiber between the first cladding light stripper and the optical fiber output and situated to extract at least a portion of backward-propagating cladding light in the optical fiber. ### Claim 2 (depends on 1) The system of claim 1, further comprising: a heat sink situated to receive and absorb the forward-propagating cladding light and the backward-propagating cladding light extracted by the first and second cladding light strippers, respectively. ### Claim 3 (depends on 1) The system of claim 1, further comprising: a detection chamber optically situated between the first and second cladding light strippers. ### Claim 4 (depends on 1) The system of claim 1, wherein less than about 10% of the forward-propagating cladding light and less than about 10% of the backward-propagating cladding light propagates in the optical fiber between the first and second cladding light strippers. ### Claim 5 (depends on 1) The system of claim 1, further comprising: a combiner associated with the laser source and including a central input and one or more other inputs adjacent to the central input; a core light detector optically coupled to the central input of the combiner and situated to detect backward-propagating core light. ### Claim 6 (depends on 1) The system of claim 1, wherein the first cladding light stripper is situated to extract 100 W or more of forward-propagating cladding light and wherein the second cladding light stripper is situated to extract 100 W or more of continuous or transient backward-propagating cladding light. ### Claim 7 A method, comprising: directing a material processing laser beam from a laser source along an optical fiber to a beam delivery fiber of a beam directing optical system, the beam directing optical system including an output beam combiner situated to combine the received laser beam from the optical fiber with one or more other laser beams; directing the material processing beam from an output end of the beam delivery fiber to a target with a beam directing optical system fiber; receiving a returned portion of the material processing laser beam returned from the target; coupling the returned portion into the beam delivery fiber; extracting at least a portion of forward-propagating cladding light associated with the material processing laser beam in a first cladding light stripper of the optical fiber optically coupled to the beam delivery fiber; and extracting at least a portion of backward-propagating cladding light associated with the returned portion of the material processing laser beam in a second cladding light stripper of the optical fiber optically situated between the first cladding light stripper and the output end of the beam delivery fiber. ### Claim 8 A method, comprising: providing a first cladding light stripper between a laser source and a beam delivery fiber output situated in relation to a target, the first cladding light stripper situated to receive a material processing beam and to extract forward-propagating cladding light associated with the material processing beam from the beam delivery fiber; providing a combiner associated with the laser source and including a central input and one or more other inputs adjacent to the central input; providing a core light detector optically coupled to the central input of the combiner and situated to detect backward-propagating core light; extracting backward-propagating cladding light from the beam delivery fiber with a second cladding light stripper, the second cladding light stripper disposed between the first cladding light stripper and the beam delivery fiber output and situated to receive the material processing beam from the first cladding light stripper and to receive backward-propagating cladding light associated with the target; detecting a characteristic associated with the backward-propagating cladding light extracted with the second cladding light stripper from the beam delivery fiber delivering the material processing beam generated with the laser source; detecting a characteristic associated with backward-propagating core light in the beam delivery fiber; and adjusting one or more laser system characteristics in response to one or more of the detected backward-propagating cladding light and backward-propagating core light characteristics. ### Claim 9 (depends on 8) The method of claim 8, wherein the one or more adjusted laser system characteristics includes a power level of one or more pump beams associated with the laser source. ### Claim 10 A system, comprising: a first cladding light stripper disposed between a laser source and a beam delivery fiber output situated in relation to a target, the first cladding light stripper situated to receive a material processing beam and to extract forward-propagating cladding light associated with the material processing beam from the beam delivery fiber; a second cladding light stripper disposed between the first cladding light stripper and the beam delivery fiber output and situated to receive the material processing beam from the first cladding light stripper and to receive backward-propagating cladding light associated with the target, the second cladding light stripper situated to extract backward-propagating cladding light from the beam delivery fiber; a combiner associated with the laser source and including a central input and one or more other inputs adjacent to the central input; and a core light detector optically coupled to the central input of the combiner and situated to detect backward-propagating core light. ### Claim 11 (depends on 10) The system of claim 10, further comprising: a beam directing optical system situated to receive the laser beam from the output of the optical fiber. ### Claim 12 (depends on 11) The system of claim 11, wherein the beam directing optical system includes an output beam combiner situated to combine the received laser beam with one or more other laser beams. ### Claim 13 (depends on 10) The system of claim 10, further comprising: a core light detector situated between the first and second cladding light strippers to detect a material processing beam core light power level. ### Claim 14 (depends on 13) The system of claim 13, wherein the core light detector is situated to receive core light associated with an optical splice that is positioned between the first and second cladding light strippers. ### Claim 15 (depends on 10) The system of claim 10, further comprising: a detector coupled to the second cladding light stripper and situated to detect one or more characteristics associated with the backward-propagating cladding light. ### Claim 16 (depends on 15) The system of claim 15, wherein the characteristics associated with the backward-propagating cladding light include one or more of temporal, spectral, thermal, and power characteristics. ### Claim 17 (depends on 15) The system of claim 15, further comprising: a laser interlock coupled to the detector so as to receive the characteristics associated with the backward-propagating cladding light from the detector and responsive to adjust characteristics of the material processing beam based on the characteristics associated with the backward-propagating cladding light. ### Claim 18 (depends on 15) The system of claim 15, wherein the detector includes one or more of a thermistor, thermal switch, and photodiode. ### Claim 19 (depends on 10) The system of claim 10, further comprising a laser system aiming beam coupled to the central input of the combiner. ### Claim 20 (depends on 10) The system of claim 10, further comprising a beam dump coupled to the central input of the combiner. ### Claim 21 (depends on 10) The system of claim 10, wherein the combiner is a pump or pump-signal combiner.