# Nanostructuring of LNOI for efficient edge coupling

## TL;DR

This paper reports on the design, fabrication, and characterization of nanostructured LNOI inverse tapers for efficient fiber-to-chip edge coupling, achieving low insertion losses and analyzing the effects of crystal cut on performance.

## Contribution

It introduces optimized nanostructured inverse tapers for LNOI, demonstrating improved coupling efficiency and analyzing the impact of crystal orientation on device performance.

## Key findings

- Achieved a 2.5 dB/facet butt-coupling loss with optimized tapers.
- Identified the influence of crystal cut on mode matching performance.
- Demonstrated low propagation loss in fabricated waveguides.

## Abstract

We present the design, fabrication and characterization of LNOI fiber-to-chip inverse tapers for efficient edge coupling. The etching characteristics of various LNOI crystal cuts are investigated for the realization of butt-coupling devices. We experimentally demonstrate that the crystal cut limits the performance of mode matching tapers. We report a butt-coupling loss of 2.5 dB/facet and 6 dB/facet by implementing 200 nm tip mode matching tapers in $+Z$-cut LNOI and $X$-cut MgO:LNOI waveguides with low propagation loss. We anticipate that these results will provide insight into the nanostructuring of LNOI and into the further development of efficient butt-coupling in this platform.