Refractive Index Sensor Based on Metal-Clad Planar Polymer Waveguide Operating at 850 nm
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Refractive Index Sensor Based on Metal-Clad Planar Polymer Waveguide Operating at 850 nm Lanting JI, Wei WEI, Gang LI, Shuqing YANG, Yujie FU, Juan SU, and Chi WU* Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China *
Corresponding author: Chi WU
E-mail: [email protected]
Abstract: A metal-clad planar polymer waveguide refractive index sensor based on epoxy (EPO) polymer materials by using light intensity interrogation at 850 nm is designed. The polymethyl methacrylate (PMMA) material is deployed as the low refractive index (RI) buffer layer in order to better couple the optical guided mode and the surface plasmon polaritons (SPP) mode for working in water environment. The effects of the gold film thickness, PMMA buffer layer thickness, waveguide layer thickness, waveguide width, and gold length on the sensor sensing characteristics have been comprehensively studied. Simulation results demonstrate that the normalized transmission increases quasi-linearly with the increment of RI of the analyte from 1.33 to 1.46. The sensitivity is 491.5 dB/RIU, corresponding to a high RI resolution of 2.6×10–9 RIU. The designed SPP-based optical waveguide sensor is low-cost, wide-range, and high-precision, and has a broad application prospect in biochemical sensing with merits of miniaturization, flexibility, and multiplexing. Keywords: Metal-clad optical waveguide sensor; intensity interrogation; refractive index of liquid Citation: Lanting JI, Wei WEI, Gang LI, Shuqing YANG, Yujie FU, Juan SU, et al., “Refractive Index Sensor Based on Metal-Clad Planar Polymer Waveguide Operating at 850 nm,” Photonic Sensors, DOI: 10.1007/s13320-020-0606-1.
1. Introduction Refractive index (RI) is a critical parameter of liquid closely related to density, concentration, and temperature. The monitoring of RI of liquid is very important in fields of chemistry, medicine, physics, biology, and production practices. Surface plasmon polariton (SPP) is a kind of electromagnetic waves propagating along the metal-dielectric interface and has a sensitive response to the variation of RI of dielectric adjacent to the metal film [1, 2]. The surface plasmon resonance (SPR) technology has now penetrated into the fields of food, biology, and environment, and demonstrated many advantages, such as high sensitivity, real-time detection, label-free, and selective recognition [3–7]. Due to
the wavevector mismatch with optical waves, SPP waves are traditionally excited by using the Kretschmann or Otto prism based on attenuated total reflection, which has disadvantages of large volume, complex system, and high cost [8–10]. Then, the integrated optical waveguide technology is exploited to fabricate SPR sensor chips with advantages of low cost, small size, and easy integration [11–13]. The planar optical waveguide structure is used as the coupling channel, which avoids the complex prism system and is easy to interact with the external system. The waveguide-type SPR sensor can integrate the sensing area of the SPR with other semicond
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