Hydrogen Detection Using a Functionalized Photonic Crystal Vertical Cavity Laser

Abstract

A thin layer of palladium (Pd) was deposited on the surface of an etched air hole photonic crystal (PhC) vertical cavity surface emitting laser (VCSEL) to form a hydrogen gas (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) sensor. H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> reacts with Pd, forming PdH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> , which induces a shift in the complex refractive index. With Pd on its surface, the reflectivity of the top distributed Bragg reflector depends on the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentration. We present device operation theory and experimental results showing a 60% output power increase and a 52 pm redshift of the lasing wavelength at 4% H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Since the PhC VCSEL laser is single mode and the wavelength shift is comparable to the laser linewidth, the sensor can provide an accurate quantification of the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentration over the range of 0-4% H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .