# High-Sensitivity and Temperature-Robust Gas Sensor Based on Magnetically Induced Differential Mode Splitting in InSb Photonic Crystals

## TL;DR

A new gas sensor using InSb photonic crystals and magnetic effects achieves high sensitivity and temperature stability for detecting low-refractive-index gases like methane and carbon monoxide.

## Contribution

A novel magneto-optical differential photonic crystal sensor (MO-DPCS) that combines magnetic splitting and angular interrogation for high sensitivity and thermal robustness.

## Key findings

- The MO-DPCS achieves a differential sensitivity of 30.8°/RIU with a magnetic field of 0.033 T.
- The sensor reduces temperature-induced drift to below 0.35° across a 1 K range using differential detection.
- The detection limit is 4.18 × 10−4 RIU, enabling precise sensing of low-refractive-index gases.

## Abstract

High-precision detection of hazardous gases with low refractive indices ranging from 1.000 to 1.100, specifically including methane, carbon monoxide, and sulfur dioxide, is critical for industrial safety, yet conventional sensors often suffer from limited sensitivity and severe thermal cross-sensitivity. This work presents a Magneto-Optical Differential Photonic Crystals Sensor (MO-DPCS) utilizing indium antimonide (InSb) to address these constraints. Employing the Multi-Objective Dragonfly Algorithm (MODA), the system was inversely optimized to maximize magneto-optical polarization splitting while rigorously maintaining an ultra-high transmission efficiency. Crucially, an angular interrogation architecture operating under oblique incidence was established to maximize the magneto-optical non-reciprocity, where the detection was realized by fixing the terahertz source frequency and monitoring the precise angular displacements of the steep spectral edges. A differential detection technique was employed to utilize the non-reciprocal phase changes wherein Transverse Electric (TE) and Transverse Magnetic (TM) modes display contrasting kinematic characteristics in the presence of an external magnetic field. The findings indicate that with an adjusted magnetic field of 0.033 T, the MO-DPCS attains an exceptional differential sensitivity of 30.8°/RIU, much above the 0.8°/RIU seen in the unmagnetized condition. The differential approach efficiently eliminates common-mode thermal noise, minimizing temperature-induced drift to below 0.35° across a 1 K range. The suggested MO-DPCS offers a robust, self-referencing solution for stable and high-sensitivity gas sensing applications with a detection limit of 4.18 × 10−4 RIU.