Abstract
Heavy mass ions, Kr and Xe, having energies in the approximately 10 MeV/amu range have been used to produce thick planar optical waveguides at the surface of lithium niobate (LiNbO3). The waveguides have a thickness of 40-50 micrometers, depending on ion energy and fluence, smooth profiles and refractive index jumps up to 0.04 (lambda = 633 nm). They propagate ordinary and extraordinary modes with low losses keeping a high nonlinear optical response (SHG) that makes them useful for many applications. Complementary RBS/C data provide consistent values for the partial amorphization and refractive index change at the surface. The proposed method is based on ion-induced damage caused by electronic excitation and essentially differs from the usual implantation technique using light ions (H and He) of MeV energies. It implies the generation of a buried low-index layer (acting as optical barrier), made up of amorphous nanotracks embedded into the crystalline lithium niobate crystal. An effective dielectric medium approach is developed to describe the index profiles of the waveguides. This first test demonstration could be extended to other crystalline materials and could be of great usefulness for mid-infrared applications.
Highlights
Ion implantation of light ions (H or He) in the few-MeV energy range is a standard procedure to produce optical waveguides at visible and near-IR wavelengths in LiNbO3 and in many other crystals [1,2,3]
It implies the generation of a buried low-index layer, made up of amorphous nanotracks embedded into the crystalline lithium niobate crystal
LiNbO3 samples irradiated with high-energy Kr or Xe ions (Table 1) show a surface layer that acts as an optical waveguide
Summary
Ion implantation of light ions (H or He) in the few-MeV energy range is a standard procedure to produce optical waveguides at visible and near-IR wavelengths in LiNbO3 and in many other crystals [1,2,3]. The idea behind the fabrication of an optical waveguide with high-energy ions is to bombard the material with ions having their electronic energy loss maximum at a certain depth inside the material At and around this maximum, the damage threshold can be overcome producing an amorphous layer of lower refractive index. The purpose of this work has been to explore the use of the heavy ion irradiation method, in the electronic energy loss regime to even higher energies (~10 MeV/amu) and stopping powers This would allow the fabrication of much thicker waveguides (up to tens of microns) with ultralow fluences (< 1012 cm−2). Energy Energy Se surface Se max Sn max Rp (MeV) (MeV/amu) (keV/nm) (keV/nm) (keV/nm) (μm)
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