Analysis and design of Integrated optical biosensors with intermediate buffer layers

Abstract

The objective of this thesis is to analyse photonic integrated biosensor. Photonic integrated biosensor are choosen for analysis as it is offering high sensitivity, miniaturization to nano scale and high stability. PIC biosensor in this analysis are operated at wavelength 1500nm to 1600nm. Refractive Index sensing technique is used for detecting bioanalytes generally blood glucose. In this thesis proposed four layer waveguide configuration in which additional buffer layer sandwiched between core Silicon and Substrate Silicon dioxide for enhancing performance of device. Initially applied the four layer concept to slab waveguide which is 1D structure and mathematically formulated characteristic equations applying boundary conditions. Extended idea of buffer layer to ridge waveguide which is 2D structure. In ridge waveguide the effective refractive index is evaluated using effective index method. Considered three different buffer material namely Flourinated silicon dioxide, Silicon Oxynitride and Silicon nitride. Explored which buffer material suitable for which device and the buffer thickness requirement is analysed. Flourinated Silicon Dioxide buffer material choosen in applications where penetration depth is important. So flourinated silicon dioxide buffer layer applied for Racetrack Ring Resonator biosensor and Racetrack Ring Assisted Mach-Zehnder Interferometer biosensor. Silicon Oxynitride layer is used where there is a need of balance between confinement and penetration depth. So silicon oxynitride material is used layer in devices like directional coupler and analysed. Silicon Nitride buffer layer is used when confinement is prime requirement.It also enhance resonantn depth of Racetrack Ring Assisted Mach-Zehnder Interferometer Silicon Nitride buffer layer enhance sensitivity in devices like slot waveguide biosensor where analyte has close interaction with buffer. In this work proposed a novel Rounded Rectangular Ring Resonator biosensor which enhances sensitivity by increasing effective length of ring. The applied intermediate buffer layer which will further increases Sensitivity. After analysis of different layer configuration we focused on analyte properties. Finally considered three layer configuration with complex refractive index bio analyte and analysed how biosensor detection varies in presence of complex refractive index bioanalyte. Then added buffer and studied how it impacts sensitivity of imaginary part of Racetrack Ring Resonator biosensor