Characterisation of proton-exchange slab optical waveguides in x-cut LiNbO3

Abstract

The paper reports on a systematic study of planar optical waveguides in X-cut LiNbO 3 fabricated by the proton-exchange technique. The extent of the exchange process was monitored by measuring the infrared absorption peak at 3510 cm" 1 . It was established that the waveguide profile could be accurately modelled by a step index change with An = 0.127 at X o -632.8 nm and An = 0.096 at X o = 1150 nm. From the mode effective refractive index measurements, the effective diffusion coefficients for the exchange process were calculated. A value for the activation energy for the proton-exchange process was established. The effect of off-Y-axis propagation on the mode effective indices of the waveguide was studied. A waveguide mode cutoff at 29° from the C-axis was established. The lowest optical losses measured in single-mode planar waveguides were 1.4 dB/cm at X o = 632.8 nm and 1.3 dB/cm at X o = 1150 nm for light propagating normal to the C-axis.

Chemical environment and occupation sites of hydrogen in LiMO3

“…Nevertheless, our BVEL energy values are in good agreement with experimental results, which state an activation energy for hydrogen species in a range of (0.92–1.4) eV. 19,82–88 According to the study by Liu et al 106 the hydrogen activation energy for near-stoichiometric material is given as 1.05 eV and 1.10 eV for LiNbO 3 and LiTaO 3 , respectively. This also indicates that the calculated stoichiometric site with its theoretically lower activation energy is not occupied by hydrogen (see Table 4).…”

“…As shown in a number of previous works, the hydrogen in LiMO 3 crystals is very mobile and can be removed under reducing atmospheres and high temperatures or incorporated in a wet environment. 19,[82][83][84][85][86][87][88] In this work, hydrogen incorporation was conducted in a H 2 O saturated atmosphere at a temperature of 1173 K for 10 h (see Fig. 5a).…”

Research of selective etching in LiNbO3 using proton-exchanged wet etching technique

“…First and for most, it is quite necessary to figure out the precise PE process in order to understand the proposed PEWE method. It mainly involves in-diffusion process of protons ions (H + ) from a proton source and outdiffusion process of interstitial ions (Li + ) from the LN crystal lattice [26], the whole process can be summarized by the following chemical reaction [27,28]:…”

Fabrication techniques of lithium niobate waveguides

“…High stability over a period of 8 months, low optical losses (0.5-1 dB/cm), low in-plane scattering levels ( -50 dB at 1° in air), and good electro-optic property, have been achieved for x-and z-cut samples. A systematic study of planar optical waveguides in z-and x-cut samples is reported in Reference 60 and continued in Reference [61].…”