On chip, high-sensitivity thermal sensor based on high-Q polydimethylsiloxane-coated microresonator

A high-sensitivity thermal sensing is demonstrated by coating a layer of polydimethylsiloxane (PDMS) on the surface of a silica toroidal microresonator on a silicon wafer. Possessing high-Q whispering gallery modes (WGMs), the PDMS-coated microresonator is highly sensitive to the temperature change in the surroundings. We find that, when the PDMS layer becomes thicker, the WGM experiences a transition from redshift to blueshift with temperature increasing due to the negative thermal-optic coefficient of PDMS. The measured sensitivity (0.151 nm/K) is one order of magnitude higher than pure silica microcavity sensors. The ultrahigh resolution of the thermal sensor is also analyzed to reach 10(-4) K. (C) 2010 American Institute of Physics. [doi:10.1063/1.3457444]