High-Precision Electromagnetic Tuning of Fabry–Pérot Filters for Gas Detection

Accurate gas detection is essential for mitigating harmful gas emissions and ensuring production safety. This study introduces an FR4-based tunable Fabry-Pérot (F-P) filter equipped with an electromagnetic actuator to address the precision limitations of conventional gas detectors. Simulations and analyses were performed on distributed Bragg reflectors (DBRs) with various multilayer film configurations on silicon and silicon dioxide substrates. Results indicate that a five-layer (poly-Si/SiO2) membrane stack reflector achieves a high reflectance of 98.51%, enabling the filter to attain a full width at half maximum (FWHM) of 0.9 nm and a free spectral range (FSR) of 173.6 nm. To overcome the challenges of limited cavity length control in the F-P cavity, a novel electromagnetically actuated cascaded folded beam structure, designed via finite element analysis, is proposed. This mechanism achieves a reflector displacement of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6~\mu $ </tex-math></inline-formula>m under a low actuating voltage of 30 mV while maintaining a parallelism finesse exceeding 300. Additionally, the system achieves a displacement tuning precision of 22.7 nm/mA, surpassing existing designs, and the displacement adjustment error below 20 nm. Experimental validation demonstrated an excellent linear correlation (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}} =0.9998$ </tex-math></inline-formula>) between the applied signals and reflector displacements, facilitating precise wavelength control. The proposed methane detection system, based on the electromagnetic F-P tunable filter, exhibits significant potential for high-precision methane monitoring in environmental and industrial applications.