Optics Communications 478 (2021) 126372 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom Design of dual polarized tetra core PCF based plasmonic RI sensor for visible-IR spectrum Amit Kumar Shakya, Surinder Singh ∗ Department of Electronics and Communication Engineering, Sant Longowal Institute of Engineering and Technology, Sangrur, Punjab, India ARTICLE INFO Keywords: RI sensor PCF SPR Wavelength sensitivity Sensor resolution Amplitude sensitivity Linearity ABSTRACT In this research work, a susceptible refractive index (RI) biosensor has been presented which can operate in visible to near-infrared region, i.e (500–2000 nm) on a tetra core ‘‘photonic crystal fiber (PCF)’’ based on the ‘‘surface plasmon resonance (SPR).’’ The efficiency of the proposed RI sensor is analyzed in terms of ‘‘wavelength sensitivity (WS), amplitude sensitivity (AS), sensor resolution (SR), and linearity of the resonance wavelength.’’ Using amplitude interrogation method, maximum AS of 7200  −1 is obtained for  − polarization and 4725  −1 for  − polarization, respectively. Similarly WS of 5000 nm  −1 and 10000 nm  −1 is obtained using a wavelength interrogation method for  − and  − polarization, respectively. Maximum SR of 2.00×10 −5  and 1.00×10 −5  is obtained for  − polarization and  − polarization, respectively. The maximum WS, AS, and SR are obtained for the analyte having a RI value of 1.335. A linear relation between resonant wavelength and RI produces  2 =0.9832 and 0.9761 for  − and  − polarization, respectively. 1. Introduction The last few decades have witnessed the evolution of sophisticated sensing devices for various utilizations like organic chemical detection, biochemical detection, environmental monitoring, and medical diag- nostics [1]. These sensing devices are known as sensors, and when an investigation is done on the basis of the refractive index, they become RI sensors [2]. Nowadays, PCF is widely used for sensor designing because the structural parameters of the PCF can be easily modified as per requirement, which was not even imagined in the past [3]. The PCF has got several advantages like power fraction, birefringence, chromatic dispersion, waveguide dispersion, and various nonlinear applications [3]. To date, several sensing techniques are available like micro-ring resonators, fiber Bragg grating, multimode interference, and surface plasmon resonance (SPR) are widely explored [4]. Among all the sensing techniques, SPR sensors are used in many sectors. This is due to the feasibility of PCF-SPR sensors. As PCF offers high flexibility in shape and design, it can also control the evanescent field with assists in propagating light within a single mode as well as in core to excite surface plasmons. The PCF has several other advantages like increased sensitivity and wide sensing range, which can be obtained by carefully creating the PCF structure [5]. The plasmonic property of the PCF SPR sensor is widely used in designing highly sensitive RI sensors. In the PCF SPR sensor, surface plasmon polariton (SPP) interacts with the leaky core at a specific wavelength. This wavelength is called a ∗ Corresponding author. E-mail address: surinder_sodhi@rediffmail.com (S. Singh). resonance wavelength [5]. At this resonant wavelength, the real part of core mode and plasmonic mode (SPP) become equal, and resonance condition is achieved. The SPP mode shows a high degree of sensitivity towards a slight change in analyte RI [5]. This results in the shift in wavelength from higher to lower or vice versa resulting in the detection of analyte RI. Several plasmonic materials have been used in the sensor to date, and these include Gold (Au), Silver (Ag ), Graphene, Copper (Cu), Titanium dioxide (  2 ) and several conducting oxides (TCOs), etc. Among all these plasmonic material, Au is considered as a good and reliable plasmonic material for different sensor structures as it is free from the oxidation problem. In literature, we have found several types of PCF structures like D shaped PCF, tapered fibers, two-mode fiber, hollow-core fiber, and twin-core fiber [6]. If we consider the plasmonic material deposition methodology, then there are three sensing methodologies D shaped structure, internal metal deposition (IMD) technique, and external metal deposition (EMD) technique [4]. Recently, Rifat et al. [7] have used the IMD technique to design an internal metal-coated RI sensor. They have obtained AS of 1420  −1 and WS of 11,000 nm  −1 . Their sensor have obtained suitable sensing parameters (AS, WS, and SR), but the challenge was IMD in which plasmonic material deposition and selective liquid infiltration are performed on-air holes surface. Thus IMD is a very challenging task https://doi.org/10.1016/j.optcom.2020.126372 Received 16 May 2020; Received in revised form 18 July 2020; Accepted 10 August 2020 Available online 12 August 2020 0030-4018/© 2020 Elsevier B.V. All rights reserved.