Suspended whispering gallery mode resonators made of different polymers and fabricated using drop-on-demand inkjet printing for gas sensing applications

Investigation of drop-on-demand inkjet printing as a fabrication method for an optical gas sensor reveals its potential to incorporate multiple sensing materials on a single microchip. Through this additive method, three distinct polymers—SU-8, polystyrene (PS), and polyhexamethylene biguanide (PHMB)—were deposited onto a silicon substrate and suspended, allowing the polymer microdroplets to expand freely. The coupling to these whispering gallery mode resonators with a tapered optical fiber allows measuring high quality factors exceeding 106. The gas sensing capabilities of all three polymers were studied for three different gases: isopropanol, water, and carbon dioxide. Sensitivities of up to 0.25 pm/ppmv and limits of detection as low as 14 ppmv were achieved.