# US 12,771,088 B2 · Very large mode area single-mode amplifying optical fiber and fiber amplifier or laser incorporating the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,771,088 B2 - Document ID: US12771088B2 - Status: Granted - Kind: B2 - Application number: 18/254,108 - Filed: 2021-11-22 - Published: 2024-03-21 - Granted: 2026-10-20 - Earliest claimed: 2020-11-24 - Assignees: Photonics Bretagne - Applicants: Photonics Bretagne - Inventors: Laurent Provino; Thierry Taunay - Web page: https://patentgrep.com/patent/US12771088B2 ## CPC - H01S 3/06733: {Fibre having more than one cladding} - H01S 3/06712: {Polarising fibre; Polariser} - H01S 3/08045: Single-mode emission - H01S 3/094007: {Cladding pumping, i.e. pump light propagating in a clad surrounding the active core} - H01S 3/1623: {chromium, e.g. Alexandrite} - 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 Disclosed is a very large mode area single-mode amplifying optical fiber including a doped core having a core diameter larger than 20 micrometers, surrounded by at least a first cladding including a solid matrix made of a first glass and two stress applying parts arranged symmetrically with respect to the core, the two stress applying parts being aligned along an alignment axis, the cladding including two flat surfaces extending parallel to the longitudinal axis and transverse to the alignment axis, the two flat surfaces being joined by two rounded surfaces and wherein the optical fiber is suitable for being bent with a bending diameter less than 30 cm in a plane forming an angle of less than 15 degrees with the alignment axis while having bending losses below 0.5 dB/m. ## Claims ### Claim 1 Very-A very large mode area single-mode amplifying optical fiber comprising: a core extending along a longitudinal axis of the optical fiber, the core being solid and doped with elements presenting at least one emission band, the core having a core diameter larger than 30 micrometers, said core being surrounded by at least one glassy cladding comprising a first cladding comprising a solid matrix made of a first glass and two stress applying parts disposed symmetrically with respect to the core, the first glass having a lower refractive index than the core, the core and the two stress applying parts being aligned along an alignment axis transverse to the longitudinal axis, the core having a numerical aperture comprised between 0.038 and 0.054, wherein the at least one glassy cladding comprises, on its outer periphery, two and only two flat surfaces extending parallel to the longitudinal axis and being perpendicular to the alignment axis, the two flat surfaces being disposed symmetrically with respect to the core and being joined by two rounded surfaces having a shape of an arc of a circle, and wherein the optical fiber is configured to be bent with a bending diameter comprised between 10 cm and 30 cm in a plane comprising the longitudinal axis of the fiber and said plane forming an angle of less than 15 degrees with the alignment axis while having bending losses for the fundamental mode less than 0.5 dB/m and bending losses equal or greater than 10 dB/m for high order modes. ### Claim 2 (depends on 1) The very large mode area single-mode amplifying optical fiber according to claim 1, wherein the bending diameter is comprised between 10 cm and 20 cm, with bending losses for the fundamental mode less than 0.5 dB/m. ### Claim 3 (depends on 1) The very large mode area single-mode amplifying optical fiber according to claim 1, wherein the optical fiber is bent in a plane forming an angle of less than 10 degrees with the alignment axis. ### Claim 4 (depends on 1) The very large mode area single-mode amplifying optical fiber amplifier according to claim 1, wherein said very large mode area single-mode amplifying optical fiber presents an effective area greater than 450 μm2. ### Claim 5 (depends on 1) The very large mode area single-mode amplifying optical fiber according to claim 1, wherein the core and first glass are based on silica glass or on fluoride glass or on chalcogenide glass or on phosphate glass. ### Claim 6 (depends on 1) The very large mode area single-mode amplifying optical fiber according to claim 1, wherein the core is doped with rare earth ions or with chromium ions. ### Claim 7 (depends on 1) The very large mode area amplifying optical fiber according to claim 1, wherein the core presents a flat-top or a parabolic refractive index profile, or wherein the core comprises a pedestal surrounding a central part of the core, the pedestal having a refractive index lower than the central part of the core and higher than the first glass. ### Claim 8 (depends on 1) The very large mode area single-mode amplifying optical fiber according to claim 1, wherein the at least one glassy cladding consists of the first cladding, the first cladding comprising, on its outer periphery, the two flat surfaces. ### Claim 9 (depends on 1) The very large mode area single-mode amplifying optical fiber according to claim 1, wherein the at least one glassy cladding comprises a second cladding arranged around the first cladding, the second cladding having a lower refractive index than the first glass. ### Claim 10 (depends on 9) The very large mode area single-mode amplifying optical fiber according to claim 9, wherein the second cladding is selected from an all solid cladding made of a second glass or an air cladding and a solid cladding made of a second glass, the air cladding being arranged between the first cladding and the solid cladding made of the second glass. ### Claim 11 (depends on 1) The very large mode area single-mode amplifying optical fiber according to claim 1, further comprising a polymer or metal cladding around said at least one glassy cladding. ### Claim 12 (depends on 1) A fiber amplifier comprising: the very large mode area single-mode amplifying optical fiber according to claim 1, said very large mode area single-mode amplifying optical fiber being spooled with a bending diameter less than 30 cm. ### Claim 13 (depends on 12) The fiber amplifier according to claim 12, wherein said very large mode area single-mode amplifying optical fiber has a length comprised between 50 cm and 20 m. ### Claim 14 (depends on 12) The fiber amplifier according to claim 12, further comprising a pump source generating a pumping beam and an optical beam combiner adapted for injecting said pumping beam into the core and/or into the first cladding. ### Claim 15 (depends on 1) A fiber laser comprising: the very large mode area single-mode amplifying optical fiber according claim 1, said very large mode area single-mode amplifying optical fiber being spooled with a bending diameter less than 30 cm; a light source generating a source beam to be amplified; a first mirror at a first end of the very large mode area single-mode amplifying optical fiber; and a second mirror at a second end of the very large mode area single-mode amplifying optical fiber. ### Claim 16 (depends on 13) The fiber amplifier according to claim 13, further comprising a pump source generating a pumping beam and an optical beam combiner configured to inject said pumping beam into one or more of the core and the first cladding.