Polymer Waveguide Coupled Surface Plasmon Refractive Index Sensor: A Theoretical Study
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Polymer Waveguide Coupled Surface Plasmon Refractive Index Sensor: A Theoretical Study Lanting JI, Shuqing YANG, Rongna SHI, 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 waveguide coupled surface plasmon sensor for detection of liquid with high refractive index (RI) is designed based on polymer materials. The effects of variation of the thickness of the Au film, polymethyl methacrylate (PMMA) buffer, and waveguide layer on the sensing performance of the waveguide are comprehensively investigated by using the finite difference method. Numerical simulations show that a thinner gold film gives rise to a more sensitive structure, while the variation of the thickness of the PMMA buffer and waveguide layer has a little effect on the sensitivity. For liquid with high RI, the sensitivity of the sensor increases significantly. When RI of liquid to be measured increases from 1.45 to 1.52, the sensitivity is as high as 4518.14 nm/RIU, and a high figure of merit of 114.07 is obtained. The waveguide coupled surface plasmon RI sensor shows potential applications in the fields of environment, industry, and agriculture sensing with the merits of compact size, low cost, and high integration density. Keywords: Waveguide; surface plasmon polaritons; polymer; refractive index sensor Citation: Lanting JI, Shuqing YANG, Rongna SHI, Yujie FU, Juan SU, and Chi WU, “Polymer Waveguide Coupled Surface Plasmon Refractive Index Sensor: A Theoretical Study,” Photonic Sensors, DOI: 10.1007/s13320-020-0589-y.
1. Introduction As one of the most important physical parameters of liquid, refractive index (RI) reflects the essential characteristics of liquid and is closely related to temperature, concentration, density, and thermal coefficient. Therefore, in the field of physical, chemical, biological, medical, environmental research and production practice, the monitoring of liquid RI variation is more and more important. Surface plasmon polaritons (SPPs) are electromagnetic waves coupled with free electron density oscillations that propagate along the interface between a metal and a dielectric medium [1–3]. The mode field distributions of the SPP mode are highly localized in the vicinity of the
metal surface and exhibit significant response to the variation of external RI near the metal. SPP-based sensors have been widely used in food safety, medical diagnosis, and biochemical sensing fields with merits of high sensitivity, label-free, and real-time detection [4–13]. Due to the mismatch of propagation constants, the SPPs cannot be excited directly by light waves. Many excitation configurations have been reported, in which Kretschmann or Otto prisms [14–16], gratings [17], waveguides [18], and fibers [19] are popular ones. A variation of the RI of medium will produce a change in the propagation constant of the SPP waves that alters the coupling condition between the light waves and SPP waves. Most of plasmo
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