The formation of waveguides and modulators in LiNbO3 by ion implantation

Abstract

Ion implantation is an attractive method for writing optical circuits for use in integrated optics. In LiNbO3 it is shown that there are large changes produced in both refractive indices n0 and ne by the energy deposited in nuclear collisions between the implanted ions and the lattice. The process is insensitive to ion species and at 300 K a universal curve exists for the decrease of n0 as a function of deposited energy by nuclear collisions. Saturation changes of −6% occur at 300 °K, and larger values are noted for 77 K implants. The saturation condition is reached after the deposition of ∼1022 keV cm−3 from the ion beams. Because the indices are reduced, ion beams have been used to write low index boundaries to define waveguiding regions. By using energetic light ions (e.g., 2-MeV He+) negligible change is produced in the surface layer where the energy loss is primarily electronic and thus the low index region is formed deep within the solid. The computed and measured mode characteristics are in good agreement. The guides show complex annealing characteristics but absorption losses are negligible after annealing at 200 °C. Guiding action exists after heat treatments up to some 400 °C. The surface layers retain crystallinity and electro-optic properties; as a demonstration of this we report results from three-dimensional modulators formed by helium-ion implantation.

Buried amorphous layers by electronic excitation in ion-beam irradiated lithium niobate: Structure and kinetics

“…This is also the case for high-fluence irradiations with light ions ͑H and He͒, where nuclear losses are dominant. 3,22 On the other hand, the heavily damaged region presents a very faint Raman spectrum, consisting of weak remnants of the sharp peaks of the crystalline phase on top of a relatively large background and with broad features at 630 and 830 cm −1 which have been previously associated with amorphous LiNbO 3 produced by different physicochemical methods. 24,25 They have been associated with distorted and/or defective oxygen octahedra with partial oxygen deficiency.…”

“…For sufficiently high fluences, the profile approaches a steplike shape, whose bottom level reaches a limit value, n = 2.10, approximately independent of the investigated ions as well as of light polarizations and coincides with the refractive index of amorphous LiNbO 3 . 15,22 The profiles reached at this stage for F, Mg, and O irradiations are comparatively illustrated in Fig. 4.…”

He Ion Implantation and the Refractive Index Depth Profile in Relaxor Ferroelectric Optical Waveguides

“…The refractive index in a wide range of implanted materials has been shown to follow a depth profile qualitatively similar to that of the volume density of the energy deposited into lattice atoms by the nuclear stopping of the implanted ions. 1,3,[6][7][8] This suggests that a similar framework could be employed to predict the n(z) that results from implanting He in PZN-PT.…”

Annealing behavior of lithium niobate irradiated with He-ions at 100K

“…Furthermore, the chemical resistance is reduced. As a consequence the damaged regions are etched in a hydrofluoric solution (HF) without affecting the non irradiated crystal [5][6][7][8]. In combination with selective ion irradiation using standard masking technologies this allows the fabrication of high quality micro-and nano-structures with high aspect ratios and low roughness in LiNbO 3 [9,10].…”