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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    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
    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


    Workshop15th International Laser Physics Workshop, LPHYS 2006
    Abbreviated titleLPHYS
    Internet address


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


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