# US 2020/0287345 A1 · Methods to maintain and control the polarization state from 3c optical fiber > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2020/0287345 A1 - Document ID: US20200287345A1 - Status: Published application - Kind: A1 - Application number: 16/809,314 - Filed: 2020-03-04 - Published: 2020-09-10 - Earliest claimed: 2019-03-05 - Assignees: nLIGHT, Inc. - Applicants: nLIGHT, Inc. - Inventors: Tyson Lowder - Web page: https://patentgrep.com/patent/US20200287345A1 ## CPC - H01S 3/302: {in an optical fibre} - H01S 3/06712: {Polarising fibre; Polariser} - H01S 3/06737: {Fibre having multiple non-coaxial cores, e.g. multiple active cores or separate cores for pump and gain} - H01S 3/094003: {the pumped medium being a fibre} - G02B 6/105: {having optical polarisation effects} - G02B 6/14: Mode converters - G02B 6/4458: {Coiled, e.g. extensible helix} - H01S 3/06704: {Housings; Packages} - H01S 3/1603: {rare earth} - 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 - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract Fiber laser amplification systems and methods are disclosed for use with a chirally coupled core (3C) optical fiber enabling the generation of a high-power output beam having a controlled stable polarization state. Vector modulation instabilities which typically induce undesirable sidebands in 3C fiber optics are greatly reduced even at high peak powers, enabling operation of the up to power levels limited mainly by stimulated Raman scattering (SRS). Polarization extinction ratios (PER) demonstrate long-term stability and minimal degradation due to changes in system temperature. Delays in reaching stable operation during start-up are also greatly reduced. ## Claims ### Claim 1 An apparatus, comprising: a 3C fiber wound a number of turns about a coiling axis between an input end and an output end of the 3C fiber to form a 3C fiber coil such that a number of twists in the 3C fiber with the input end and output end extended to form a straight fiber configuration is smaller than the number of turns, wherein the input end is situated to receive a beam with an input circular polarization state and the wound 3C fiber is configured to amplify the beam to produce an amplified output beam with an output circular polarization state and to reduce a polarization state variability of the output circular polarization state based on the smaller number of twists and the input circular polarization state. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the 3C fiber includes an actively doped core configured to amplify an input beam propagating from the input to the output end. ### Claim 3 (depends on 2) The apparatus of claim 2, further comprising a seed source optically coupled to the input end of the 3C fiber and configured to generate a seed beam that becomes the amplified output beam. ### Claim 4 (depends on 3) The apparatus of claim 3, further comprising a pump source optically coupled to the input end and/or the output end of the 3C fiber and configured to optically pump the actively doped core of the 3C fiber. ### Claim 5 (depends on 4) The apparatus of claim 4, further comprising an input polarization converter including a half-wave plate situated to receive the seed beam and to adjust an angle of a linear polarization state of the seed beam and including a quarter-wave plate situated to receive the seed beam with the angled-adjusted linear polarization state and to change the linear adjusted polarization state to the input circular polarization state. ### Claim 6 (depends on 5) The apparatus of claim 5, further comprising a polarization maintaining fiber situated to receive the seed beam from the seed source and to direct the seed beam to the input polarization converter. ### Claim 7 (depends on 6) The apparatus of claim 6, wherein the input polarization converter is fiber spliced at an input end to the polarization maintaining fiber and at an output end to the input end of the 3C fiber. ### Claim 8 (depends on 5) The apparatus of claim 5, further comprising an output polarization converter including a quarter-wave plate situated receive the amplified output beam and to change the output circular polarization state of the amplified output beam to a linear polarization state and including a half-wave plate situated to receive the amplified output beam with the linear polarization state and to adjust an angle of the linear polarization state of the amplified output beam. ### Claim 9 (depends on 1) The apparatus of claim 1, further comprising an optical fiber rotator coupled to at least one of the input end or the output end of the 3C optical fiber and configured to rotate the corresponding input end or output end to selectively vary the number of twists. ### Claim 10 (depends on 1) The apparatus of claim 1, wherein the 3C fiber coil is a right-handed coil. ### Claim 11 (depends on 1) The apparatus of claim 1, wherein the 3C fiber coil is a left-handed coil. ### Claim 12 (depends on 1) The apparatus of claim 1, wherein the 3C fiber includes a reference marking on an exterior surface of the 3C fiber between the input end and the output end to provide an indication of a twisting of the 3C fiber. ### Claim 13 (depends on 1) The apparatus of claim 1, wherein the number of turns is one or greater, and the number of twists is zero. ### Claim 14 (depends on 1) The apparatus of claim 1, wherein a number of quasi-twists of the 3C fiber in the 3C fiber coil is uniformly provided between the input end and output end. ### Claim 15 (depends on 1) The apparatus of claim 1, wherein the polarization state variability corresponds to a time-dependent variation in polarization extinction ratio during an optical pulse and/or over multiple optical pulses. ### Claim 16 (depends on 1) The apparatus of claim 1, further comprising a subsequent gain stage coupled to the amplified output beam and configured to amplify the amplified output beam. ### Claim 17 (depends on 1) The apparatus of claim 1, further comprising a non-linear optical element situated to receive the amplified output beam and to produce a non-linearly converted optical beam. ### Claim 18 A method, comprising: coupling a circularly-polarized input beam into a 3C fiber wound a number of turns about a coiling axis between an input end and an output end of the 3C fiber to form a 3C fiber coil such that a number of twists in the 3C fiber with the input end and output end extended to form a straight fiber configuration is smaller than the number of turns; and amplifying the input beam having the input circular polarization state to produce an amplified output beam with an output circular polarization state having a polarization state variability based on the smaller number of twists and the input circular polarization state. ### Claim 19 (depends on 18) The method of claim 18, further comprising adjusting the number of twists to reduce the polarization state variability of the amplified output beam. ### Claim 20 (depends on 18) The method of claim 18, further comprising optically pumping the 3C fiber with a pump source.