Characterization of proton-exchange slab optical waveguides in z-cut LiNbO3

Abstract

We report the results of a systematic study on planar optical waveguides fabricated in z-cut LiNbO3 by proton exchange in benzoic acid. It was found that the refractive index varied with depth and could be accurately modeled by a step index profile with Δn=0.126. Diffusion coefficients have been calculated from mode effective refractive index measurements, assuming a step index profile, and hence a value for the activation energy for the proton exchange process has been deduced. The lowest measured optical propagation loss in single-mode waveguide at a 633-nm wavelength was 2.4 dB/cm.

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

“…The lowest propagation losses measured were 1.4 dB/cm at A o = 632.8 nm and 1.3 dB/cm at k 0 = 1150 nm. These values are similar to those obtained in our previous report on PE waveguides in Z-cut LiNbO 3 [4]. Losses may be due to difference in electric field polarisation, base material, or benzoic acid impurities.…”

“…Optical waveguides in X-, Y-, Z-cut LiNbO 3 [2][3][4] and X-cut LiTaO 3 [5] have been fabricated by this technique, using benzoic acid as the source of protons. The simple and relatively low temperature process (^240°C) makes it an attractive alternative for forming optical waveguides in LiNbO 3 and LiTaO 3 to processes such as titanium diffusion.…”

Batch process for the fabrication of LiNbO3 photonic crystals using proton exchange followed by CHF3 reactive ion etching

“…The duration of the PE steps depends on the substrate chosen. Typically, an exchange-depth of 1.5 lm corresponds to 6.5 h duration of proton exchange on X-cut substrates [16], and 12.6 h duration of proton exchange on Z-cut substrates [17]. The replacement of Li + ions with H + protons helps to prevent LiF re-deposition during the RIE step, which plays a role in both the verticality of the structures and the etch-rate [13].…”

Photoreduction of metal nanostructures on periodically proton exchanged MgO-doped lithium niobate crystals

“…1(a). 22 We have previously reported D PE z ¼ 0.084 6 0.004 lm 2 /h for congruent LN processed with the same PE conditions. 25 Thus, the MgO doping lowered the PE diffusion rate in the z-direction, consistent with the findings of Ref.…”

“…During the PE process, lithium ions (and vacancies) are replaced by hydrogen ions, which penetrate into the crystal at the surfaces exposed to the acid, via a diffusion process yielding a PE depth well-described by the Arrhenius equation. 22 Both aforementioned approaches (poling and PE) can be used to fabricate periodic arrays of either reversed ferroelectric domains or polarization-reduced regions across the crystal surface. Recently, we demonstrated that such periodic PE:LN templates 23,24 can be used to form arrays of Ag nanostructures 1,3 and that the width and height of the nanostructures can be controlled by the PE depth 25 and AgNO 3 concentration, 26 respectively.…”