Ultra Low Loss Dual Square Groove Incorporated SPR-Based PCF Sensor for Malaria Diagnosis

In this paper, we present a surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) sensor for diagnosing deadly malaria. The proposed structure adopts an external sensing scheme (ESS). We introduce a dual square groove to achieve high sensitivity by placing the plasmonic layer closer to the core region. The flat surface of the square groove is coated with a silver plasmonic metal and an overlayer of 2D material is coated onto the plasmonic layer. We compare the sensitivity obtained from the 2D MoS2 and graphene layer coating onto the silver layer. We find that MoS2 provides better sensitivity than the uncoated or graphene-coated models. Furthermore, the number of layers of MoS2 has been optimized to be 5 layers of thickness of 3.25 nm. After optimizing the various physical parameters, the proposed sensor exhibits the maximum sensitivities of 7758 nm/RIU, 9210 nm/RIU, and 12,428 nm/RIU, with the maximum spectral resolution of 1.29 x 10-5, 1.09 x 10-5, 8.04 x 10-6 RIU for the schizont, trophozoite, and ring phases, respectively. Besides, we also compute the amplitude sensitivities and they are 354.57, 387.71, and 339.34 RIU-1 with the maximum amplitude resolution of 8.2 x 10-6, 4.9 x 10-6, and 2.06 x 10-6 for the schizont, trophozoite, and ring phases, respectively. Furthermore, we also investigate the other important characteristics of the proposed sensor such as signal-to-noise ratio (SNR), full-width half maximum (FWHM) of the peak, and figure of merit (FOM). In addition to the high sensitivity, the proposed structure also exhibits ultra-low loss for detection. Hence, our sensor can be driven using a low-power source through which the experimental implementation is simplified. However, most of the reported sensors show high loss which limits the fabrication feasibility. Though there are many PCF sensors reported for various disease diagnoses, PCF-based malarial diagnosis sensors are less investigated. The other reported works use costly gold as a plasmonic layer and unstable 2D materials like MXENE. As gold exhibits a high damping factor compared to silver, it affects the detection accuracy and leads to high power loss. The selection of an appropriate hybrid structure with the combination of metal-2D material is crucial for achieving good sensing performance and cost-effective fabrication. Thus, we choose the cost-effective silver and 2D material that can be easily synthesized aiding in a cost-friendly batch production process. As there has been a need for an SPR-based PCF malarial sensor that could exhibit a good sensing performance, cost-effective fabrication, and ultra-low power consumption, we firmly believe that the proposed sensor would definitely fulfill the above-mentioned traits.