Chip scale humidity sensing based on a microfluidic infiltrated photonic crystal

This work presents an optical on-a-chip humidity sensor based on the hydroscopic behavior of an infiltrated liquid into the sub-micron holes of a silicon photonic crystal. Direct measurements of the liquid refractive index in combination with numerical simulations show that the sensitivity of the device is due to changes of both the liquid's refractive index and volume. We report humidity sensing with a response time of 0.1 ms and study the stability and reversibility of the sensor. This demonstration highlights the sensitivity offered by optofluidics in photonic crystal circuits and the potential for realizing ultra-compact integrated humidity sensing components. (c) 2013 AIP Publishing LLC.