# KAIST measured optical constants of barium titanate from 193 nm to 40 µm for photonic devices

- Published: 2026-11-08 07:32 UTC
- Section: Machines & Making › Electronics
- Tags: barium titanate, BTO optical properties, Mueller matrix ellipsometry, electro-optic effect, optical modulator, refractive index, extinction coefficient, KAIST, Caltech, ACS Photonics
- URL: https://realtech.media/news/rt-d94eea141f4a415c529ecc84_kaist_measured_optical/

**KAIST and Caltech researchers determined the refractive index and absorption of barium titanate, a material for optical modulators, from ultraviolet to far-infrared.**

![KAIST measured optical constants of barium titanate from 193 nm to 40 µm for photonic devices](https://realtech.media/media/2026/11/69767fa1e16b15a9.jpg)
*newspim.com*

KAIST announced on November 8 that a team from its School of Electrical Engineering, together with Caltech, the Korea Research Institute of Standards and Science (KRISS) and J.A. Woollam, has determined the refractive index and light absorption of barium titanate (BTO) from the ultraviolet to the far-infrared, according to newspim.com [1]. The results were published online in ACS Photonics on October 20 [1].

## Why BTO was hard to characterize

Barium titanate has a pronounced electro-optic effect: its optical properties change when an electric field is applied. For this reason it is considered a material for optical modulators and other optical communication components that carry electrical signals on light [1].

The material, however, contains domains, small crystalline regions with different orientations. Responses to light from several directions mix, which made it difficult to measure the intrinsic optical properties [1].

## Measurements and results

The team used Mueller matrix spectroscopic ellipsometry, which records how the polarization of light changes on transmission or reflection. They analyzed two single-crystal samples with a relatively uniform domain orientation to reduce the mixing effect [1]. The range from 193 nm to 40 µm was divided into three bands, each analyzed separately. This gave the refractive index and absorption as a function of wavelength and crystal orientation [1].

A separate measurement of transmitted light was added. With it, the extinction coefficient was quantified down to the 10⁻⁵ level in the 2–10 µm range [1]. This information is needed to predict absorption losses in components that guide or confine light. The authors also proposed a method to calculate the response of a whole multi-domain crystal from the orientation and fraction of each domain [1].

According to KAIST, the data can be used to design optical modulators, devices that generate light at new wavelengths, and circuits that handle quantum information with light [1]. The first authors are a KAIST doctoral student and Nina Hong of J.A. Woollam; the corresponding authors are a KAIST professor and Harry Atwater of Caltech [1].

## Sources

1. [newspim.com](https://www.newspim.com/news/view/20261106000275)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-d94eea141f4a415c529ecc84_kaist_measured_optical/