# US 11,029,464 B2 · Hollow-core photonic crystal fiber and method of manufacturing thereof > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,029,464 B2 - Document ID: US11029464B2 - Status: Granted - Kind: B2 - Application number: 16/611,350 - Filed: 2018-05-07 - Published: 2020-05-28 - Granted: 2021-06-08 - Earliest claimed: 2017-05-17 - Assignees: Max-Planck-Gesellschaft zur Forderung der Wissenschaften e.V. - Applicants: Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. - Inventors: Sebastian Thomas Bauerschmidt; Patrick Sebastian Uebel; Philip St. J. Russell - Web page: https://patentgrep.com/patent/US11029464B2 ## CPC - G02B 6/02328: {Hollow or gas filled core} - G02B 6/02304: {Core having lower refractive index than cladding, e.g. air filled, hollow core} - G02B 6/2552: {reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS ## Abstract A hollow-core photonic crystal fiber (HC-PCF) (10) for guiding at least one mode of a light field (1) along a mode guiding section (11) of the HC-PCF (10), comprises an outer jacket (12), an inner cladding (13) and a hollow core (14), which extend along the HC-PCF (10), wherein the inner cladding (13) is arranged on an interior surface of the outer jacket (12) and comprises anti-resonant structures (15) surrounding the hollow core (14), and the hollow core (14) has a mode guiding core diameter (d) provided along the mode guiding section of the HC-PCF (10), and wherein at least one fiber end (16) of the HC-PCF (10) has a light field coupling section (17) in which the hollow core (14) is tapered over an axial coupling section length from a fiber end core diameter (D) at the at least one fiber end (16) to the mode guiding core diameter (d). Furthermore, methods of using the HC-PCF and manufacturing the HC-PCF are described. ## Claims ### Claim 1 A hollow-core photonic crystal fiber (HC-PCF), being configured for guiding at least one mode of a light field along a mode guiding section of the HC-PCF, comprising: an outer jacket, an inner cladding, and a hollow core, that extend along the HC-PCF, wherein: the inner cladding is arranged on an interior surface of the outer jacket and comprises anti-resonant structures surrounding the hollow core, and the hollow core has a mode guiding core diameter (d) provided along the mode guiding section of the HC-PCF, wherein at least one fiber end of the HC-PCF has a light field coupling section in which the hollow core is tapered over an axial coupling section length from a fiber end core diameter (D) at the at least one fiber end to the mode guiding core diameter (d), wherein the outer jacket has a constant thickness, and wherein the inner cladding thickness decreases towards an opening of the at least one fiber end. ### Claim 2 (depends on 1) The hollow-core photonic crystal fiber of claim 1, wherein: the anti-resonant structures have a cross-sectional dimension that gradually increases in the light field coupling section towards the mode guiding section. ### Claim 3 (depends on 1) The hollow-core photonic crystal fiber of claim 1, wherein: the fiber end core diameter (D) and the axial coupling section length are selected such that an overlap of the inner cladding and the light field to be focused to the hollow core for guiding by the HC-PCF is excluded or negligible at the fiber end. ### Claim 4 (depends on 1) The hollow-core photonic crystal fiber of claim 1, wherein: the axial coupling section length of the light field coupling section is at least the mode guiding core diameter (d) and/or at most a transition dimension (π(D2d2−d4)0.5/(4λ)), where λ is the central wavelength of the light field. ### Claim 5 (depends on 4) The hollow-core photonic crystal fiber of claim 4, wherein: the axial coupling section length of the light field coupling section is at least 20 μm and/or at most 5000 μm. ### Claim 6 (depends on 1) The hollow-core photonic crystal fiber of claim 1, wherein: the anti-resonant structures have rounded ends facing toward the at least one fiber end. ### Claim 7 (depends on 1) The hollow-core photonic crystal fiber of claim 1, wherein: the inner cladding extends to an opening of the at least one fiber end. ### Claim 8 (depends on 1) The hollow-core photonic crystal fiber of claim 1, wherein: the light field coupling section is provided at an incoupling end of the HC-PCF only. ### Claim 9 (depends on 1) The hollow-core photonic crystal fiber of claim 1, wherein: the HC-PCF is configured to subject a light field to an optically nonlinear process, in particular spectral broadening, or the HC-PCF is configured to deliver a light field to an application site. ### Claim 10 (depends on 1) The hollow-core photonic crystal fiber of claim 1, wherein the light field coupling section is formed by thermal treatment of the HC-PCF. ### Claim 11 (depends on 10) The hollow-core photonic crystal fiber of claim 10, wherein: resonant structures of the inner cladding are softened and the light field coupling section is formed by the effect of surface tension in the softened anti-resonant structures. ### Claim 12 (depends on 11) The hollow-core photonic crystal fiber of claim 11, wherein: the thermal treatment comprises a heating of the HC-PCF such that the resonant structures of the inner cladding are softened and the light field coupling section is formed by the combined effect of surface tension in the softened anti-resonant structures and an applied vacuum in at least one of the anti-resonant structures. ### Claim 13 (depends on 11) The hollow-core photonic crystal fiber method of claim 11, wherein: the thermal treatment comprises a heating of the HC-PCF such that the resonant structures of the inner cladding are softened and the light field coupling section is formed by the combined effect of surface tension in the softened anti-resonant structures and an applied pressure in the mode guiding core. ### Claim 14 A hollow-core photonic crystal fiber (HC-PCF), being configured for guiding at least one mode of a light field along a mode guiding section of the HC-PCF, comprising: an outer jacket, an inner cladding, and a hollow core, that extend along the HC-PCF, wherein: the inner cladding is arranged on an interior surface of the outer jacket and comprises anti-resonant structures surrounding the hollow core, and the hollow core has a mode guiding core diameter (d) provided along the mode guiding section of the HC-PCF, wherein at least one fiber end of the HC-PCF has a light field coupling section in which the hollow core is tapered over an axial coupling section length from a fiber end core diameter (D) at the at least one fiber end to the mode guiding core diameter (d), and wherein an axial transition length over which the fiber core diameter dimension reduces in the light field coupling section from the fiber end core diameter (D) to (0.5*(D+d)) is at least 0.5 times the mode guiding core diameter (d) and/or at most 0.5 times a transition dimension (π(D2d2−d4)0.5/(4λ)), where λ is the central wavelength of the light field. ### Claim 15 (depends on 14) The hollow-core photonic crystal fiber of claim 14, wherein: the axial transition length is at least 10 μm and/or at most 1000 μm. ### Claim 16 A hollow-core photonic crystal fiber (HC-PCF), being configured for guiding at least one mode of a light field along a mode guiding section of the HC-PCF, comprising: an outer jacket, an inner cladding, and a hollow core, that extend along the HC-PCF, wherein: the inner cladding is arranged on an interior surface of the outer jacket and comprises anti-resonant structures surrounding the hollow core, and the hollow core has a mode guiding core diameter (d) provided along the mode guiding section of the HC-PCF, wherein at least one fiber end of the HC-PCF has a light field coupling section in which the hollow core is tapered over an axial coupling section length from a fiber end core diameter (D) at the at least one fiber end to the mode guiding core diameter (d), and wherein the inner cladding does not extend to an opening of the at least one fiber end.