Fabrication of planar optical waveguides in LiB/sub 3/O/sub 5/ by 2 MeV He/sup +/ ion implantation

The fabrication of planar optical waveguides in LiB/sub 3/O/sub 5/ is discussed. Using 2-MeV /sup 4/He/sup +/ implantation with a dose of 1.5*10/sup 16/ ions/cm/sup 2/ at 300 K, the refractive indexes of a 0.2- mu m-thick layer 5.1 mu m below the crystal surface are reduced to form optical barrier guides. For this ion dose the maximum change from the bulk values of refractive index at a wavelength of 0.488 mu m are 1.5%, 5.25%, and 4% for n/sub x/, n/sub y/, and n/sub z/, respectively. The refractive indexes of the guiding region change by less than 0.02% from the bulk values. The dose dependence of the optical barrier height has been measured. A threshold ion dose of about 0.75*10/sup 16/ ions/cm/sup 2/ is required to form a refractive index barrier and ion doses higher than about 2.5*10/sup 16/ ions/cm/sup 2/. saturate the refractive index decrease. Waveguide propagation losses for annealed single energy implants of dose 1.5*10/sup 16/ ions/cm/sup 2/ are dominated by tunneling and are estimated to be approximately 8.9 dB/cm for the z-cut waveguides used. Multiple energy implants broaden the optical barrier, and losses of <4 dB/cm have been observed.<
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