Fabrication and evaluation of deep-proton-exchanged and annealed waveguides in MgO:stoichiometric-LiTaO₃

Abstract

We developed deep-proton exchanged (DPE) and annealed waveguides in MgO:stoichiometric-LiTaO3 crystal. We performed DPE in pyrophosphoric acid at 230 °C for 20 min and measured mode size and depth dependent on the annealing duration. High-quality planar waveguides of a mode size as large as 20 µm, suitable for electro-optic spatial light modulators for 355 nm UV wavelength, were obtained by annealing for 200 h.

Buried annealed proton-exchanged waveguide in periodically-poled MgO:LiTaO3 fabricated by surface-activated bonding for high-power wavelength conversion

“…( 4), and the diffusion coefficient D a along the Z direction for a temperature of 400 °C was estimated to be 1.3 μm 2 h −1 , which was similar to that of MgO:SLT (0.9 μm 2 h −1 ) estimated by the mode size of the waveguide. 28) The refractive index profile of the buried APE waveguides was calculated using the estimated diffusion coefficients D PE and D a . The process was assumed to first perform the PE in a pure pyrophosphoric acid at 230 °C on a MgO:SLT crystal with a channel waveguide-shaped mask, followed by direct bonding with a non-PE MgO:SLT crystal and annealing at 400 °C.…”

“…[21][22][23] Specifically, annealed proton-exchanged (APE) waveguides with a guided mode diameter of several microns are widely used. [24][25][26][27][28] The APE waveguides have a graded refractive index profile and show low scattering loss. 25) For a high-power wavelength conversion, however, the power density of the lights tends to exceed the above photorefractive damage threshold.…”

Enlargement of mode size in annealed proton-exchanged periodically-poled MgO doped stoichiometric LiTaO3 waveguide for high power second harmonic generation

“…For the channel waveguide with a large mode size, weak confinement waveguides, waveguides with a small index difference between core and cladding regions as well as a graded-index profile, are desirable to suppress higher-order guided modes. The annealed proton-exchanged (APE) waveguides are widely used in LiNbO 3 and LiTaO 3 [19][20][21][22][23][24][25] which are fabricated by proton exchanging with lithium ions in a high-temperature acid and successive thermal diffusion of the protons. 21) By controlling the temperature and duration for both thermal processes, the amount and distribution of the protons can be optimized for obtaining the weak-confinement channel waveguide with a large-cross-section graded-index profile.…”

“…21) By controlling the temperature and duration for both thermal processes, the amount and distribution of the protons can be optimized for obtaining the weak-confinement channel waveguide with a large-cross-section graded-index profile. 25) Additionally, the APE waveguides exhibit inherently low scattering loss due to being free from steep refractive index changes. 20) In this work, as a first step toward a high-power UV light source consisting of the SHG and SFG devices, we fabricated an APE channel waveguide with a large mode size in a PP MgO:SLT crystal and demonstrated SHG at a wavelength of 515 nm.…”