Design of fabrication friendly & highly sensitive surface plasmon resonance-based photonic crystal fiber biosensors

Abstract

Many researchers have shown their excellence in the field of PCF-based SPR biosensors. In recent years, great designs showing high sensing performance have been proposed. However, the challenge for designing is that most of the designs either exhibit high sensitivity but have a drawback of having higher confinement loss or showing low sensitivity with lower loss. Most importantly, the designs may become complicated in order to achieve high sensitivities. We tried to minimize this tradeoff, gained higher sensitivities with considerably lower losses, and made four unique designs. Our research is distinctive, and the PCF-SPR biosensors are easy to fabricate and highly sensitive. All of our prototypes have a strategic pattern of circular air holes inside the fiber, which leads to a superior sensing performance. The evaluation of all the sensor characteristics has been done by employing the finite element method (FEM) of COMSOL Multiphysics. The gold (Au) layer used just around the fiber in our designs acts as the plasmonic material, and the layer of TiO2 increases the adhesivity of the gold and the fiber. We have optimized all the fiber parameters to achieve the best result in terms of sensitivity. We derived a maximum amplitude sensitivity (AS) of 5060 RIU−1 with a maximum sensor resolution of 1.98×10−6 from one sensor. The same sensor exhibited a maximum wavelength sensitivity (WS) of 41500 nm/RIU with a maximum sensor resolution of 2.41×10−6 . Moreover, the maximum figure of merit (FOM) procured was 1068.7 for this sensor. This sensor has also shown a fabrication tolerance limit of ±10%. Additionally, the temperature and strain sensitivities of that sensor are estimated to be 0.75 nm/◦C and 3 pm/με, respectively, along with a resolution (temperature) of 1.33×10−1 ◦C. Another sensor of ours showed an excellent birefringence of 2.23×10−3 , whereas all other performance parameter values were almost identical. One of the remaining sensors exhibited extremely low confinement loss. The maximum value of confinement loss for that sensor was found to be 3.73 dB/cm, which is extraordinary. The last sensor is exceptional in the sense that we have analyzed its performance for two different plasmonic materials (Gold and AZO) and found that it can sense analytes with very low refractive indices when AZO is used. The overall analyte sensing range of all our sensors is 1.31 to 1.43. All the designs are discussed elaborately in our thesis in the upcoming chapters. With their enhanced performance in terms of sensitivity, we believe that our SPR based PCF biosensors can potentially contribute a lot in detecting unknown analytes and medical diagnostics applications.