Thermo-Optic Property Measurement Using Surface Plasmon Resonance-Based Fiber Optic Sensor

Abstract

The temperature disturbances greatly influence the performances of microfluidic chips during the working process. It is therefore important to evaluate the thermo-optic properties of microfluidic materials. Here, we measure the thermo-optic property by employing a fiber optic surface plasmon resonance (SPR) sensor combined with a thermocouple. This setup can be applied for embedding in microfluidic materials or directly detecting fluidic samples. Three fiber optic SPR sensors were fabricated with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$400~\mu m$ </tex-math></inline-formula> -bare-core, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$600~\mu m$ </tex-math></inline-formula> -bare-core and mismatched-core structures. The thermo-optic responses of the three sensors were compared to determine the optimum sensor structure. The thermo-optic property of polydimethylsiloxane was then investigated over the full temperature detection range of 25–200 °C. The thermo-optic coefficient of polydimethylsiloxane was determine to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 4.19\times 10^{-4}$ </tex-math></inline-formula> RIU/°C, which agrees well with previous reports. The thermo-optic properties of ethanol and brine were also evaluated to confirm the universality of the proposed measurement method. To our knowledge, this is the first reported detection of thermo-optic properties using a fiber optic SPR sensor.