# Characterisation of Inhomogeneities in Ti:LiNbO$_3$ waveguides

## TL;DR

This study characterizes fabrication imperfections in titanium in-diffused lithium niobate waveguides using spectral analysis, providing insights into the limitations of current UV photolithography for optimizing integrated photonic devices.

## Contribution

It offers a detailed analysis of fabrication errors in lithium niobate waveguides, linking imperfections to spectral performance and enabling better device optimization.

## Key findings

- Fabrication errors match theoretical models.
- Imperfections can be reconstructed from spectral data.
- Quantifies limits of UV photolithography in waveguide fabrication.

## Abstract

Nonlinear processes in integrated, guiding systems are fundamental for both classical and quantum experiments. Integrated components allow for compact, modular and stable light-processing systems and as such their use in real-world systems continues to expand. In order to use these devices in the most demanding applications, where efficiency and/or spectral performance are critical, it is important that the devices are fully optimized. In order to achieve these optimizations, it is first necessary to gain a thorough understanding of current fabrication limits and their impact on the devices final performance. In this paper we investigate the current fabrication limits of titanium in-diffused lithium niobate waveguides produced using a masked photolithographic method. By dicing a long (~cm) sample into smaller pieces and recording the resulting phasematching spectra, the fabrication error present in the UV photolithographic process is characterized. The retrieved imperfections fit well with theoretical expectations and from the measured imperfection profile it is shown that one can directly reconstruct the original distorted phasematching spectrum. Therefore, our measurements directly quantify the intrinsic limitations of the current standard UV photolitographic technique for the realization of integrated waveguides in lithium niobate.