Investigation of Ytterbium Incorporation in Lithium Niobate for Active Waveguide Devices

Abstract

In this work, we report on an investigation of the ytterbium diffusion characteristics in lithium niobate. Ytterbium-doped substrates were prepared by in-diffusion of thin metallic layers coated onto x- and z-cut congruent substrates at different temperatures. The ytterbium profiles were investigated in detail by means of secondary neutral mass spectroscopy, optical microscopy, and optical spectroscopy. Diffusion from an infinite source was used to determine the solubility limit of ytterbium in lithium niobate as a function of temperature. The derived diffusion parameters are of importance for the development of active waveguide devices in ytterbium-doped lithium niobate.

Integrated Photonics Based on Rare‐Earth Ion‐Doped Thin‐Film Lithium Niobate

“…Before concluding this section, we note that for all the ion‐doping methods introduced in this section, the concentration limit only depends on the solid solubility ( C max ) of the RE element in LiNbO 3 . [ 77,96,97 ] For example, the solubility of Nd ( C max = 0.25 mol% at 1300 K) is experimentally determined to be only half that of Er ( C max = 0.5 mol% at 1300 K, corresponding to an ion concentration of 10 20 ion cm ‐3 ) in LiNbO 3 . [ 96 ] The solubility generally increases with the temperature, but it does not depend on the crystal cut.…”

“…Nevertheless, ion in‐diffusion is a fairly flexible approach for RE ion doping into photonic chips since it offers the full spectrum of spatially varying doping with required ions. [ 76–78 ] Thus, it is possible to have gradually varied ion concentrations, or even very different ion species, doped at desired substrate areas or within a particular photonic device, while the rest sections remain undoped. Despite a number of technological challenges still exist, thermal ion in‐diffusion is very promising for easy implementation of multiple RE ion doping of a monolithic photonic chip based on, e.g., thin‐film LNOI.…”

“…[ 76 ] d,e) The depth profiles of Yb in ion‐in‐diffused LiNbO 3 ( x ‐cut and z ‐cut) annealed at different temperatures, analyzed by secondary neutral mass spectrometry (SNMS). [ 77 ] b,c) Reproduced with permission. [ 76 ] Copyright 2014, SPIE; d,e) Reproduced under the terms of the Creative Commons Attribution 4.0 International license (CC BY 4.0).…”

“…Recently, furthermore, the very same research group achieves breakthroughs in ion in-diffusion of Yb 3+ -and Nd 3+ -doped thinfilm LNOI platforms, demonstrating emission spectra and crosssections very close to that of doped bulk LiNbO 3 . [77][78][79][80] In all these abovementioned studies, ion in-diffusion is carried out at temperatures within the high-temperature stability range of the ferroelectric phase of LiNbO 3 (900-1142 °C) for 30 (for Er 3+ and Yb 3+ ion in-diffusion) or 200 h (in case of Nd 3+ ion in-diffusion). [76][77][78] Furthermore, on-chip ridge waveguides (fabricated by precise diamond blade dicing [81] ) with fluorescence properties comparable to their respective bulk-doped LiNbO 3 waveguide counterparts have been demonstrated.…”

“…b,c) Reproduced with permission [76]. Copyright 2014, SPIE; d,e) Reproduced under the terms of the Creative Commons Attribution 4.0 International license (CC BY 4.0) [77]. https://creativecommons.org/licenses/by/4.0 Copyright 2020, The Authors, published by MDPI.…”