Planar optical waveguides formed by helium ion implantation in lithium niobate

• Main Author: Naden, J. M.
• Published: University of Surrey 1985
• Subjects: 535; Optics & masers & lasers
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355414

A buried layer of damaged material with reduced refractive indices can result from implantation of MeV He[+] ions into LiNbO[3]. The extent and distribution of this damage and the resultant refractive index profiles are found to depend on the ion energy, ion dose and implant temperature. Typical values of ion energy and dose are 1.5 MeV and 10[16] He[+] cm-2 respectively at room temperature, producing a change of -1.5% in n[o]. Provided that the small amount of damage created in the surface layer is removed by low temperature annealing (typically for 30 minutes at 200°C in a flowing oxygen atmosphere), this structure is capable of acting as an optical waveguide with the light confined in the surface layer. A prism coupler has been used to excite the individual modes of waveguides formed in this way and to determine their propagation constants and attenuations. For the values given above, 2 TM (ordinary) modes and 1 TE (extraordinary) mode are supported in Y-cut, X-propagating material at 633 nm wavelength, with fundamental mode attenuations of between -6 and -7 dB cm[-1]. These optical properties are shown to be sensitive to both implantation and annealing process parameters and, from the results, it is inferred that ordinary mode behaviour is determined solely by ion damage effects, but that extraordinary mode behaviour is influenced additionally by lithium outdiffusion. Additional results are presented showing the wavelength dependence of the optical properties in the near infra-red region, and further conclusions are drawn regarding the distribution and movement of the ion damage. It is suggested that both the damage profile and feature size may vary with changes in implantation and annealing conditions. Finally, suggestions are made regarding the possible directions of future work which may lead to practical integrated optical devices.