Optical sensor for humidity and hydrogen gas based on polymer microresonators

We report humidity and hydrogen sensors employing elastic polymer (SU-8) optical microresonators fabricated with photolithography. The sensing mechanism relies on monitoring the spectral shifts of the optical whispering gallery modes (WGMs) in the transmission spectra recorded from the microresonators. WGMs are excited through SU-8 waveguides in which a tunable laser light is coupled from an optical fiber.