# Multifunctional lithium niobate platform for photodetection and photoacoustic and thermoelastic gas sensing

## TL;DR

A new on-chip device using lithium niobate combines multiple sensing techniques for efficient gas detection at very low concentrations.

## Contribution

The novel contribution is a multifunctional platform integrating photodetection, photoacoustic, and thermoelastic sensing on a single chip.

## Key findings

- The platform achieves parts-per-billion detection limits for multiple gases.
- It enables system-level integration with a quantum cascade laser and transimpedance amplification on a printed circuit board.
- The device supports second-harmonic measurements for carbon monoxide detection.

## Abstract

Leveraging the intrinsic multi physics nature of ferroelectric lithium niobate, we present a multi-functional platform (LN-MFP) that seamlessly integrates photoacoustic spectroscopy, light-induced thermoelastic spectroscopy and photodetection into a single on-chip device. The proposed LN-MFP operates over a broad spectral range spanning from the visible to the mid infrared. We experimentally demonstrate trace gas detection of nitrogen dioxide, water vapor, acetylene, carbon dioxide, methane and ammonia, achieving parts-per-billion detection limits. We implement a custom packaging solution where the LN-MFP chip and a 4.6 µm quantum cascade laser chip are mounted on a printed circuit board together with transimpedance amplification, demonstrating system-level integration. Using this co-packaged module, we demonstrate carbon monoxide detection via second-harmonic measurements, outlining a clear route towards fully integrated on-chip implementations. This compact, hybrid, multi-functional architecture markedly reduces system complexity and footprint compared with conventional benchtop systems and is intrinsically compatible with the rapidly developing lithium niobate integrated photonics ecosystem. The LN-MFP provides a core sensing building block for future all-lithium-niobate spectroscopic chips for environmental monitoring, point-of-care diagnostics and on-site chemical analysis.

Spectroscopy often relies on bulky instrumentations implementing a single technique. Here, authors propose an on-chip, lithium niobate, multi-functional platform demonstrating photodetection and gas sensing. The latter is realised through photoacoustic or thermoelastic sensing, achieving parts-per-billion detection limits.