# Integrated Optical Waveguide Electric Field Sensors Based on Bismuth Germanate

## TL;DR

This paper presents a new method for fabricating optical waveguides on bismuth germanate using femtosecond lasers, enabling precise electric field sensing.

## Contribution

A novel femtosecond laser technique for fabricating low-loss waveguides on BGO, enabling improved electric field sensing.

## Key findings

- A cladding-type waveguide on BGO with 1.2 dB/cm loss was successfully fabricated using femtosecond laser writing.
- Simulations confirmed single-mode transmission and effective light confinement in the waveguide core.
- The method enables refractive index reduction and is feasible for electric field sensor applications.

## Abstract

Bismuth germanate (Bi4Ge3O12, BGO) is a widely used optical sensing material with a high electro-optic coefficient, ideal for optical electric field sensors. Achieving high precision in electric field sensing requires fabricating optical waveguides on BGO. Traditional waveguide writing methods face challenges with this material. This study explores using femtosecond laser writing technology for preparing waveguides on BGO, leveraging ultrafast optical fields for superior material modification. Our experimental analysis shows that a cladding-type waveguide, written with a femtosecond laser at 200 kHz repetition frequency and 10.15 mW average power (pulse energy of 50.8 nJ), exhibits excellent light-guiding characteristics. Simulations of near-field optical intensity distribution and refractive index variations using the refractive index reconstruction method demonstrate that the refractive index modulation ensures single-mode transmission and effectively confines light to the core layer. In situ refractive index characterization confirms the feasibility of fabricating a waveguide with a refractive index reduction on BGO. The resulting waveguide has a loss per unit length of approximately 1.2 dB/cm, marking a successful fabrication. Additionally, we design an antenna electrode, analyze sensor performance indicators, and integrate a preparation process plan for the antenna electrode. This achievement establishes a solid experimental foundation for future studies on BGO crystal waveguides in electric field measurement applications.