Design and Performance Analysis of Photonic Crystal Waveguide for Bio – Chemical Sensing Applications

Abstract

The consistent progress of electronic equipments in different fields, especially in control technology has brought a positive impact on communication and sensing technology. Fiber optic technology has historically dominated the communication field and recently tending towards the sensing field. Sensing devices are underway to build their own optical devices in place of electronic devices due to selectivity and specificity. Derived from the same fiber optic sensor family, photonic crystal (PC) sensor technology is rapid, pathogen-specific, and does not require chemical modification of the test sample. PCs offer the possibility of controlling and manipulating light by opening a gap in the waveguide within a given range of frequencies and it may hold the key to the continued progress. In this thesis, we proposed different PC sensor designs to exploit the applications in the field of biochemical such as chemicals and food testing. Photonic crystal waveguide (PCW) design for chemical concentration detection is performed on sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) as they are highly useful in industrial and research applications. Design of PCW for foodborne pathogen detection is performed on Escherichia coli (E. coli) as it is one of the most dangerous agent of foodborne diseases. Various semiconductor materials and insulator with higher to lower refractive indices (Si, GaAs, Si3N4, and SiO2) are analyzed to fix the choice of material for PCW design. The design and analysis are performed using the finite difference time domain (FDTD) simulation method. The design exhibits two inverted J-shaped defects with center cavity designed in the shape of E. coli. In this research, DH5α strain of E. coli foodborne pathogen is considered as a model due to its shape. Simulation of PCW design is performed using infrared radiation wavelengths. Simulation analysis reports larger resonance wavelength shifts, higher sensitivities, and quality factors for Si-based PCW biosensor at an operating wavelength of 1.55 μm. Another proposed PCW design of biochemical sensor is to identify the chemical component‟s acid concentrations with a greater accuracy. The experiment is also performed to identify the refractive indices of H2SO4 and H2O2 chemical components using refractometer. The proposed design consists of circular air holes of radius 0.44a (where „a‟ is the lattice constant of 0.45 μm), arranged in a hexagonal structure on silicon on insulator (SOI). Due to the change in refractive index of the sample, resonance wavelength shifts towards higher wavelengths (red shift) with a higher coefficient of determination. The proposed design allows desired input wavelength of 1550 nm to be guided in the waveguide for an effective identification of chemical component‟s concentrations. Resolution and limit of detection are calculated as 1.2 nm and 4 × 10−2 RIU for H2SO4 solution and 0.2 nm and 2 × 10−2 RIU for H2O2 solution. Improved sensitivities with increased standard deviations are achieved after structural optimization. Further, we proposed a design of PCW sensor for chemical sensing applications at sodium doublet line (Sodium-D-line). The proposed PCW sensor is patterned on 10×10 μm silicon on insulator (SOI) wafer. PCW designed with circular air holes of radius r = 0.35a where „a‟ is the lattice constant of 0.45 μm, arranged in hexagonal structure. The principle of measurement is based on variation in refractive index of sample that causes change in effective refractive index (ERI) in guided mode leading to blue shift. Experimental results of refractive index are used in sensing analysis. The proposed design is capable of allowing sodium-D-line wavelength through structure to work as chemical and biochemical sensor. In the final design for foodborne pathogen detection, we considered E. coli cell is trapped in the middle of the PCW biosensor having three different types of waveguides, i.e., gallium arsenide/silicon dioxide (GaAs∕SiO2), silicon/silicon dioxide (Si∕SiO2), or silicon nitride/silicon dioxide (Si3N4∕SiO2) to observe the maximum resonance shift and sensitivity. It is observed from the simulation data analysis that GaAs∕SiO2 is the preferred PCW biosensor for the identification of E. coli and optimization is carried out to achieve highest sensitivity and quality factor by varying the ring slot width and radius of the design. The proposed PCW biochemical sensor designs reveal that Si and GaAs materials are suitable as an active layer for sensing applications. By using effective refractive index phenomena, wavelength shift is observed due to change in refractive index. Finally, device optimization is achieved by introducing variations in geometry of the design.