Modeling of the refractive index profile of a femtosecondwritten waveguide in LiNbO3

TL;DR

This paper analyzes the refractive index profile of femtosecond laser-written waveguides in LiNbO3, enabling better design and simulation of integrated optical circuits through modeling and experimental validation.

Contribution

It introduces a method to reconstruct the refractive index profile of femtosecond laser-written waveguides in LiNbO3 based on manufacturing parameters and experimental light coupling data.

Findings

Reconstructed refractive index profiles match experimental coupling behavior.

Modeling improves the accuracy of beam propagation simulations.

Validated waveguides demonstrate effective light coupling as predicted.

Abstract

Femtosecond laser pulse systems allows to modify in a precise and permanent way the optical properties of atransparent materials. This process enables the direct writing of guiding structures in materials, commonlyknown as waveguides, which are the base for optical circuit fabrication.It is our interest to study the main characteristics of the waveguides manufactured by the laser micro-machining technique. Here, an analysis of the resulting refractive index profile has been carried out. Thischaracteristic is essential for the design and simulation of integrated optical circuits. In particular we havedeveloped our research on the study of light coupling in a pair of type II waveguides made in Lithium Niobate(LiNbO3).These experimental backgrounds provide us with elements to adjust and test the retrieved profile.Taking into account different distance between tracks and writing energies, it is well known that the couplinglength changes and the coupling ratio too. Then this study allows us to reconstruct the refractive index profileaccording to its manufacturing conditions. Modeling of the refractive index distribution profile is a key parameterto perform beam propagation mode simulations (BPM) to achieve more realistic results. So, by means of thismethod it is possible to obtain a general procedure to describe the characteristics of these kinds of waveguides.As a model test, integrated waveguides were built to corroborate their light coupling. In a first stage it is designedthrough BPM simulations then it is manufactured in an X-cut LiNbO3crystal in order to check its operationaccording to the simulations carried out