Focused-ion-beam nano-structured rib channel waveguides in KY(WO4)2 for laser applications

F. Gardillou, Y.E. Romanyuk, M. Pavius, C.N. Borca, R.P. Salathé, Markus Pollnau

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    Abstract

    Bulk $KY(WO_4)_2$ (hereafter KYW) laser crystals doped with rare-earth ions are recognized to be among the most promising host materials for obtaining novel solid-state lasers. The rare-earth ions $RE^{3+}$ are easily incorporated in the KYW structure by replacing the $Y{3+}$ ions, resulting in a stoichiometric active material with high absorption and emission cross-sections [1]. The realization of waveguiding structures with such materials is of great interest for future active integrated optics devices. In order to achieve highly confined single-mode propagation and low optical losses, we have developed a new KYW:Yb layer co-doped with $Lu{3+}$ and $Gd{3+}$ions. A special composition of $KLu_{0.253}Gd_{0.13}Yb_{0.017}Y_{0.6}W$ has provided reproducible crack-free layers with a refractive-index contrast as high as 7.5 x $10^{-3}$, which is the highest value reported for KYW:Yb / KYW composite structures. Rib waveguides obtained by reactive ion etching (RIE) are characterized by propagation losses below 1 dB/cm at the $Yb^{3+}$-fluorescence wavelength (λ ≈ 1020 nm) and by a high optical confinement. As a consequence, they offer a great potential for the realization of efficient nano-structured waveguides such as Bragg grating filters or even DBR/DFB (Distributed Bragg Reflection/ Distributed FeedBack) micro-lasers. Here, the first promising results concerning the realization of Bragg filters on KYW by focused ion beam (FIB) etching are reported. This tool is very powerful for producing nano-structures in a large variety of materials. In this work, different thin conductive layers have been tested and a 20-nm-thick aluminum layer has been chosen to reduce charging effects. Then, FIB parameters have been optimised to etch periodical nano-scale patterns with a high aspect ratio at a high speed. The dimensions and the shape of the grating have been fixed by numerical simulations to obtain efficient rib-based Bragg filters at λ ≈ 1020 nm. Such gratings, with a periodicity as low as 250 nm and a high aspect ratio, have been milled on the KYW:Gd,Lu,Yb / KYW ribs. Current work concentrates on the optical characterization and optimization of these first Bragg filters produced in a double tungstate material.
    Original languageEnglish
    Title of host publication15th International Laser Physics Workshop (LPHYS'06)
    Subtitle of host publicationBook of Abstracts
    Place of PublicationLausanne, France
    PublisherEcole Polytechnique Fédérale de Lausanne
    Pages210-210
    Number of pages1
    Publication statusPublished - 2006
    Event15th International Laser Physics Workshop, LPHYS 2006
    - École Polytechnique Fédérale De Lausanne, Lausanne, Switzerland
    Duration: 24 Jul 200628 Jul 2006
    Conference number: 15
    https://www.lasphys.com/workshops/2006

    Workshop

    Workshop15th International Laser Physics Workshop, LPHYS 2006
    Abbreviated titleLPHYS
    CountrySwitzerland
    CityLausanne
    Period24/07/0628/07/06
    Internet address

    Keywords

    • EWI-12310
    • IR-62257
    • METIS-248241
    • IOMS-APD: Active Photonic Devices

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    Gardillou, F., Romanyuk, Y. E., Pavius, M., Borca, C. N., Salathé, R. P., & Pollnau, M. (2006). Focused-ion-beam nano-structured rib channel waveguides in KY(WO4)2 for laser applications. In 15th International Laser Physics Workshop (LPHYS'06): Book of Abstracts (pp. 210-210). Lausanne, France: Ecole Polytechnique Fédérale de Lausanne.