Formation of optical waveguides in KNbO3 by low dose MeV He+ implantation

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Abstract
MeV 4He+ implantation into single crystals of KNbO3 has been used to fabricate planar optical waveguides by generating a buried layer of lowered refractive index. We characterize the optical loss of these waveguides as a function of the ion dose D, and find a minimum loss of (1.0±0.2) cm−1 after implantation of 2 MeV ions at a dose of 5×1014 cm−2. This is by far the lowest dose ever for which efficient waveguiding has been reported. For good guides, the observed losses are mainly due to tunneling through the refractive index barrier with nontunneling contributions of less than 30%. The reduction Δnb of the refractive index nb in the region of the nuclear damage peak is proportional to the dose and we find Δnb/D=(7.8±1.6)×10−17 cm2.