Surface plasmon resonance refractive index sensor based on ultraviolet bleached polymer waveguide

- A polymer/silica hybrid waveguide is adopted to realize resonant interaction between plasmonic and optical modes.
- UV photo-bleaching method is used to form channel waveguide with refractive index difference.
- Direct optical power measurement facilitates the readout of sensing signal and the refractive index detection of organic solution.

In this paper, a compact refractive index (RI) sensor based on the resonant interaction between surface plasmon polaritons (SPP) mode and polymer waveguide mode is demonstrated. The hybrid plasmonic waveguide consists of ultraviolet (UV) sensitive SU-8 polymer and thin gold film on a silica layer. The SPP mode field is theoretically confirmed to be sensitive to the RI of analyte on the metal film surface. UV light bleaching method is adopted to fabricate the channel waveguide, which is covered by a 35 nm-thick gold layer. Microfluidic channel is used to flow organic solutions with RI of 1.52-1.60 through the sensing area. The experimental result indicates that the device has a sensitivity of 1023 dB/RIU, corresponding to a resolution of 1 × 10−6 refractive index units (RIU) at 1550 nm. The advantages of inherent feature and simple fabrication promise its potential for a portable, compact, and easily-produced refractometer.

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