Room temperature mid-infrared fiber lasing beyond 5  µm in chalcogenide glass small-core step index fiber

Nunes, J. J.; Sojka, Ł.; Crane, R. W.; Furniss, D.; Tang, Z. Q.; Mabwa, D.; Xiao, B.; Benson, T. M.; Farries, M.; Kalfagiannis, N.; Barney, E.; Phang, S.; Seddon, A. B.; Sujecki, S.

Abstract

We report mid-infrared fiber lasing for the first time above 5 µm in a room temperature, Ce 3+ doped, chalcogenide glass, step index fiber using in-band pumping with a 4.15 µm quantum cascade laser. The lasing fiber is 64 mm long, with a calculated numerical aperture of 0.48 at the lasing wavelengths, the core glass is Ge15As21Ga1Se63 atomic % (at. %), doped with 500 parts-per-million-by-weight Ce, with 9 µm core diameter, the cladding glass is Ge21Sb10Se69 at. % with 190 µm outer diameter. As pump power increases continuous wave lasing corresponding to the 2 F7/2→ 2 F5/2 transition in the Ce 3+ ion occurs at: 5.14 µm, 5.17 µm and 5.28 µm. The MIR (mid-infrared) region (defined as 3-50 µm in BS-ISO-20473:2007) enables direct molecular sensing of high selectivity/specificity. MIR fiber lasers offer excellent beam quality of bright, spatially, and temporally coherent light, routable in MIR fiber-optics for applications like narrow-band sensing, new medical laser wavelengths and pulsed-seeding of MIR-supercontinua for MIR broad-band sensing [1]. The longest wavelength room temperature CW (continuous wave) fiber lasing to date is 3.92 µm in Ho 3+-doped fluoro-indate glass fiber [2], enabled by the lower phonon energy [3] (509 cm-1) fluoro-indate glass host compared to prior fluoro-zirconate glass hosts. However, 509 cm-1 is still too high a phonon energy for laser operation > 4 µm [4]; chalcogenide glass hosts, with phonon energies down to 200 cm-1 , are prime candidates [5] for achieving this goal. Selenide-chalcogenide glasses combine sufficiently low phonon energy with good glass stability. Covalent chalcogenide glasses exhibit large linear refractive indices, so large absorption/emission cross-sections of doped-in lanthanide-ions, promising short, active devices. Chalcogenide glasses are based on sulfur 'S', selenium 'Se' and tellurium 'Te'; adding Groups 14/15 elements increases chemical /mechanical robustness. Chalcogenide fibers are weaker than silica fibers, exhibiting a Young's (elastic) modulus of ~1/5x silica [6]; and a Vickers' Hardness of ~2 GPa [7] (cf. window-glass: 5.5 GPa). Chalcogenide glasses/fiber are exceptionally stable in liquid water/water-vapor at ambient temperature, unlike fluoride glasses [8], and not oxidized in air below the glass transition temperature, beyond a protective oxide nanolayer [9] analogous to ambient silicon-oxidation [10]. Plastic-coated/uncoated chalcogenide fibers of >2 years old, stored under ambient conditions, retained respectable Ultimate Fracture Stress median: ~80 MPa [11]. Coated/uncoated fibers can maintain optical transmission for > 7 years. High optical damage thresholds are reported [12]. MIR-PL (photoluminescence) emission of lanthanide ions in selenide glasses occurs across 3-10 µm [13] wavelengths. Calculated non-radiative transition rates are orders of magnitude lower than fluoride glasses [14]. We reported first step index Pr 3+-doped chalcogenide fiber MIR-PL emission, and long millisecond MIR-PL lifetime equivalent to bulk-glass, showing fiber-processing had not compromised the lanthanide local-environment [15]. With Churbanov and Shiryaev [16] we demonstrated record low optical loss GeAsSe fiber (i.e. host-glass here). Lately, we announced gain in Pr 3+-doped selenide fiber [17]. Recently, Tb 3+ and Pr 3+ doped chalcogenide bulk glass lasers have been reported [18, 19]. Here, we report MIR fiber lasing > 5 µm in a step index selenide-chalcogenide fiber. The step index fiber (9 µm diameter core, 190 µm OD (outside diameter)) comprised core glass: 500-ppmw (parts-per-million-by-weight) Ce-Ge15As21Ga1Se63 at. % and cladding glass: Ge21Sb10Se69 at. %. The Ce 3+ ion dopant was selected due to its simple energy level structure which, in principle, excludes excited state absorption and cooperative up-conversion phenomena, whilst allowing efficient in-band pumping, with a small quantum defect. Thus, this choice mimics Yb 3+ doped silica glass, both reducing heating in the cavity and with potential for becoming the MIR analogue of the Yb 3+-doped silica glass fiber laser. There is a dearth of papers in the available literature on Ce 3+ ion doped glasses for MIR applications [20]. This contribution, apart from reporting MIR fiber lasing beyond 5 µm also displays results on Ce 3+ MIR-PL. To make the step index lasing fiber: arsenic 'As' (7N5, Furakawa Denshi), antimony 'Sb' (5N, Materion), selenium 'Se' (5N, Materion)

Citation

Nunes, J. J., Sojka, Ł., Crane, R. W., Furniss, D., Tang, Z. Q., Mabwa, D., …Sujecki, S. (2021). Room temperature mid-infrared fiber lasing beyond 5  µm in chalcogenide glass small-core step index fiber. Optics Letters, 46(15), 3504-3507. https://doi.org/10.1364/ol.430891

• Journal Article Type: Article
• Acceptance Date: Jun 3, 2021
• Online Publication Date: Jul 19, 2021
• Publication Date: Aug 1, 2021
• Deposit Date: Jul 2, 2021
• Publicly Available Date: Jul 19, 2021
• Journal: Optics Letters
• Print ISSN: 0146-9592
• Electronic ISSN: 1539-4794
• Publisher: The Optical Society
• Peer Reviewed: Peer Reviewed
• Volume: 46
• Issue: 15
• Pages: 3504-3507
• DOI: https://doi.org/10.1364/ol.430891
• Keywords: Atomic and Molecular Physics, and Optics
• Public URL: https://nottingham-repository.worktribe.com/output/5751173
• Publisher URL: https://www.osapublishing.org/ol/fulltext.cfm?uri=ol-46-15-3504&id=453373