Optical waveguide amplifier in Nd-doped glass written with near-ir ferntosecond laser pulses - Electronics Letters

InlrodJcriun: It is well known that the propertics of glass can be cliangcd by exposure lo lighl. The discoveiy by Hill [l] of thc photosensilivity of silica fibres nt UV wavclcngths and the extension of this method by Meltz [2] to a dircct-writing technique using a holographic setup has had ii major impact on guided wave device development. The UV direct-writc inethod has been used to write gratings in planar waveguides and optical fibres and even to directly write waveguidcs in bulk glasses /3]. This method, however, has inherent limitations. In particular, many glassa are not sufficiently scnsitivc to yield signi kcant changes it) refractive indcx an exposure, and hence W direct writing has becn primarily used for high-purity gennanosi1ic;ite g1;isses. Also the UV photosensitivity band is very close to thc absorption edge or most glasses, and thus the U V pcnctration depth is sinalI. This fact has precludcd tlic use of UV direct-write tecltniques to producc threedimcnsional slrtic(ures in bulk glasses. Rccently it hns becn clemonstrated that near-IR femtosecond lascr pulses can be used to induce Imlised refractivc indcx increases in a wide variety of glasses [4]. Thermally stable o p t i d wavcguides were reported in 1997 by Miura e! d. [5] in silicatc, borosilicate, clialcogenide and fluoridc glasscs. Also, inore coinplex stnictutts such as a Y-junction splitter [6] and long period gratings [7] have heen produccd. In this Letter we present for the first timc, io Ihe best of our knowledge, an flctive wwcguidc dcvicc direclly written using near1R femtosecond lascr pulses. The devimi s a waveguide amplificr in Nd-dopcd silicate glass.