Ultrasensitive Hydrogen Sensor With Vernier Effect by Dual Parallel Structured Fiber-Optic Fabry-Perot Interferometers
Maosen Guo, Hui Ding, Kechuang Han, Chunyang Han, Chen Chen
Abstract
A novel dual parallel structured fiber-optic Fabry-Perot interferometers (FPIs) for ultrasensitive hydrogen ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\mathrm{H}}_{2}}$</tex-math></inline-formula> ) sensing using the Vernier effect is proposed and demonstrated. Leveraging the high mechanical strength and chemical stability of hexagonal boron nitride (hBN), a nanoscale hydrogen-sensitive thin film of palladium (Pd)-decorated hBN is prepared and integrated with optical fiber to form a probe-type FPI hydrogen sensor. To further enhance the sensitivity, dual FPIs with similar but different cavity lengths are connected in parallel to exploit the Vernier effect, resulting in a significant amplification factor. The sensitivity of dual parallel structured FPIs based on the Vernier effect is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 14.19 nm/%, which is 9.27 times higher than that of the individual FPI within the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\mathrm{H}}_{2}}$</tex-math></inline-formula> concentration range of 0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \sim$</tex-math></inline-formula> 1%. Moreover, as the dual FPIs possess similar temperature coefficients, the Vernier effect reduces the impact of ambient temperature on the sensor, yielding a temperature coefficient as low as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \sim$</tex-math></inline-formula> 46 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}^\circ \mathrm{C}$</tex-math></inline-formula> . Additionally, the sensor offers several advantages, including good repeatability, fast response time ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \sim$</tex-math></inline-formula> 31.3 s), compact structure, easy preparation, and low cost, making it a practical solution for detecting trace amounts of hydrogen.