(This thesis report has been submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Electrical and

To the best of my knowledge and belief, the work presented here is my own original creation and does not contain any material that has been published or written by another person or that has been accepted for the award of any other university or institute degree or diploma. of higher education, except where appropriate citation has been made. The project titled “Numerical Analysis of Graphene-Based D-shaped Plasmonic Sensor for Multi-Analyte Detection” submitted by Rakib Haider & Obaidullah Bin Masum was done under my supervision and accepted as satisfactory in partial fulfillment of the requirements for the Bachelor degree . of Science in Electrical and Electronics Engineering in January 2023. Rezwanul Ahsan, Associate Professor, Department of EEE, Daffodil International University for giving us the opportunity to work on an impactful idea and taking care of every issue of developing this concept .

A systematic approach was used to look at several structural factors, such as the location, optical characteristics, shape and thickness of the metal components, that can affect how well a sensor performs. The top and bottom of the fiber are etched down to give it a double-sided D shape. The finite element method (FEM) approach is used to investigate the fiber properties and numerical sensing performance.

Due to asymmetry of the fiber structure, the proposed sensor demonstrates polarization dependence and exhibits sensing phenomena for the x-polarized state.

INTRODUCTION

• Introduction
• Motivation
• Problem statement
• Objectives

The PCF-based SPR sensor has characteristics such as compact size, high sensing accuracy, extended detection range, and design flexibility[10]. Consequently, PCF replaced prism-based SPR sensing techniques where prisms were bulky and difficult to determine the angle of incidence of light. To see where PCF-based SPR sensors are most and extensively used, refer to Fig1.1.

Intrinsic sensing, external sensing, and the D-shaped sensing approach are the three broad categories into which all published investigations of PCF-based SPR sensors can be classified to examine sensor performance [ 15 ]. Both the metal coating and the analyte can be applied externally, making the external sensing technique more straightforward than the internal sensing approach[17]. In addition to the above-mentioned issues, most PCF-based SPR sensors are designed with very small air holes ranging from about a few nm to 1–2 m in diameter, which is also complicated in practice.

Since common D-shaped fibers require more polishing depth, the goal of this work is to build an externally sensing PCF-based SPR sensor with improved sensitivity.

LITERATURE REVIEW AND TECHNICAL BACKGROUND

• overview
• Surface Plasmon and Surface Plasmon Resonance
• Surface plasmon
• Surface Plasmon Resonance
• Surface plasmon resonance sensing technique
• conventional Prism based SPR Configuration
• Photonic crystal fiber surface plasmon resonance
• Fiber Optic Technology
• Conventional optical fiber
• Photonic crystal fiber
• PCF Structure Implementation
• Geometrical definition
• Background material
• Performance Analysis Parameters
• Literature Review on PCF based SPR Sensors

The angle at which SPR occurs at thin metal surfaces is determined by the refractive index of the substance immediately adjacent to the surface. When the wave vectors of an evanescent wave and a surface plasmon wave are aligned, a decrease in the intensity of the reflected wave is seen at that angle. When the wave vectors of the surface plasmon wave and the evanescent wave coincided at a certain angle, resonance was produced.

In general, the light spreads more widely through the center of the fiber and many of the fields. In terms of their structure, a refractive index of the core is greater, while the cladding has a lower refractive index. During the manufacture of the optical fibers, protective layers of plastic are applied uniformly along the entire length of the fiber.

The refractive index of the cladding is higher than that of the cladding and core, to attenuate any unwanted light in the cladding[34]. The PCF is a single optical fiber material consisting of small air channels that run the length of the fiber. Both the core and the cladding of the fiber are typically made of fused silica (SiO2).

According to the Sellmeier equation, we can characterize the distribution of the refractive index in silica[43]. From the imaginary component of the real effective index, the birth loss can be calculated. Due to the limited number of air holes in the cladding, PCF conduction modes are inherently inefficient.

Sensor Resolution: Sensor resolution is another performance sensitivity metric that reveals the sensitivity of the sensor to detect changes in the RI of the analyte. Medical diagnostics, biomolecular detection, and antibody-antigen interaction are just some of the sensitive areas where PCF-based SPR sensing has excelled[45]. To test the PCF's sensing capabilities, the researchers varied the thickness of the gold coating.

The detection efficiency is improved by adjusting the thickness of the gold layer and the diameter of the largest air hole.

Fig 2.1: Plasmon oscillation in the metal [21].

METHODOLOGY

• Introduction
• Design Structure
• Boundary setting
• Messing
• Plasmonic Materials for the Proposed Sensor
• Research Model
• Numerical Tools

The imaginary part of the effective refractive index, the Im[neff] value, is used to determine the propagation loss. As the light passes through, some of it is scattered and reflected off the surface, which dulls the effect. The computation area can be divided into a limited number of small triangular or rectangular sections known as meshes.

Expanding the mesh in the numerical range where the light travels allows for a more precise study of the distribution. For each mesh type, the number of mesh components is indicated by the mesh size. This implies that the statistical region can be narrowed to a more manageable size, increasing the test's potential for accuracy.

The sensitivity of a PCF-based SPR sensor can be improved by the addition of plasmonic metal. Also, gold (Au) is mostly used as a plasmonic material due to its chemical stability and shows large resonance peak shift. Graphene is therefore used as an adhesive layer, which causes a larger forward shift in the resonance wavelength.

Initially, all the structural properties are used to create a D-shaped PCF sensor in COMSOL Multiphysics. Plasmonic material is used to create surface plasmon phenomena at the metal-dielectric contact (graphene, gold). A redesign of the design will be performed if the sensor performance is not sufficient compared to the literature evaluation.

Errors in the numerical solution compared to the experimental solution are acceptable, but should not be neglected. Its numerical calculation capability was used to evaluate performance metrics such as interrogation modes, birefringence, and closure loss.

Fig 3.1: (a) a cross-sectional 2D view of the PCF sensor. (b) Verification of multianalyte operation feasibility

RESULT AND DISCUSSION

• Introduction
• Multi-analyte Sensing
• Single-analyte sensing
• Sensor tolerance & optimization

The true wavelength (neff) of the core-driven mode and the SPP mode intersect at 870 nm (when RI is 1.42) in the solid orange line and dashed orange line. However, the resonant wavelength for the analyte RI of 1.36 is 616 nm, where the orange dotted line and the orange dashed line meet, representing the real(neff) of the core-driven mode and the SPP mode. It is observed that the suggested sensor exhibits high birefringence around the resonant wavelength of RI 1.36 and RI 1.41, with values ​​of 3.3×10-4 and 1.3×10-4, respectively.

Furthermore, when both channels are filled with low and high analyte RI [68], the propagating light causes the birefringence values ​​to exhibit an irregular spectrum (see Figure 4b). To confirm the feasibility of real-time operation, a spectrum study on multi-analyte detection is performed by simultaneously changing analyte RI[69]. The analyte with RI 1.42 exhibits the largest energy transfer and strongest coupling in a multi-analyte operation, with a loss depth of 149 dB/cm.

The strong relationship between the core-guided mode and the SPP mode is strongly dependent on the refractive index contrast between the fiber core and the analyte RI [70]. The difference in refractive index between the core-guided mode and the SPP mode is significant for lower analyte RI (na = 1.33), and as a result, most of the light is confined to the fiber core. However, as analyte RI increases, the difference in refractive index between the core mode and the SPP mode becomes extremely small.

The sensor becomes increasingly sensitive and shows a significant resonance wavelength shift even for smaller RI fluctuations due to strong coupling at increased analyte RI. The sensor has the lowest and maximum amplitude sensitivity for analyte RI values ​​of 1.35 and 1.40, which are approximately about 109 and 2291 RIU-1, respectively. For the proposed sensor, high birefringence of 1.45×10-4 is observed at the resonance wavelength of RI 1.41. In addition, birefringence values ​​exhibit a regular spectrum (see Figure 4.5 (b)) as a result of real-time coupling of propagating light with both channels containing the same analyte RI.

The proposed sensor is optimized by calibrating both channels using the identical analyte RI of 1.40. Fig.4.9 shows the graphene layer variation where 4.9 (a) shows confinement loss and 4.9(b) shows the wavelength sensitivity.

Fig 4.2: (a) Satisfied phase-matching condition for multi-Analyte detection. (b) Birefringence characteristics

CONCLUSION AND FUTURE WORK

Conclusion

Limitation

Future Work

Zhuang, “Highly sensitive plasmonic sensor based on double-sided polished photonic crystal fiber for component content sensing applications,” Nanomaterials , vol. Aggoun, “Multichannel photonic crystal fiber-based surface plasmon resonance sensor for multiple analyte detection,” IEEE Photonics J., vol. Guo et al., “High-sensitivity sensor based on hollow-core D-shaped microstructure fiber,” Opt.

Ahmed, “A bimetallic coated photonic crystal fiber based plasmonic refractive index sensor with low propagation loss,” Sensors (Switzerland), vol. Hasan et al., “Helical photonic crystal fiber based dual polarized surface plasmon resonance biosensor,” IEEE Sens. Skrobogatiy, “Design of the microstructured optical fiber-based surface plasmon resonance sensors with enhanced microfluidics,” Opt.

Rifat et al., “Surface plasmon resonance photonic crystal fiber biosensor: A practical sensing approach,” IEEE Photonics Technol. Singh, “A dual-channel surface plasmon resonance biosensor based on a photonic crystal fiber for multianalyte sensing,” J. Jha, “Graphene-based dual-channel photonic crystal fiber sensor using surface plasmon resonance,” IEEE Photonics Technol.

Čtyroký, “Surface plasmon resonance sensor based on a single-mode polarization-preserving optical fiber,” Sensors Actuators, B Chem., vol. Liu, “Theoretical analysis of a fully solid D-type photonic crystal fiber-based plasmonic sensor for refractive index and temperature measurement,” Opt. Lou, “A high refractive index plasmonic sensor based on d-shaped photonic crystal fibers with side-accessible hollow core,” IEEE Photonics J., vol.

Wu et al., “Surface plasmon resonance biosensor based on photonic crystal fiber of gold-coated side smooth hexagonal structure,” Opt. Yuan, “Multi-hole fiber-based surface plasmon resonance sensor operating at near-infrared wavelengths,” Opt.