GUIDED MODE RESONANCE BASED SPECTROSCOPY FOR SENSING APPLICATIONS

Abstract

This thesis focuses on design and demonstration of read-out systems based on guided mode resonance for sensing applications. The work is divided into two main parts. The first study, theoretically and experimentally, demonstrates sensitivity enhancement in dielectric guided-mode resonance (GMR) sensor via controlling a super-mode resonance at nearly cut-off diffraction (or at Rayleigh wavelength). A bulk refractive index sensitivity can reach the upper limit at a value linearly proportional to the grating’s periodicity. Super-mode excitation in the multilayer configuration of the 2D GMR sensor (a high index refractive index film coated on a low refractive index imprinted grating) is presented. This concept is verified using Rigorous Coupled Wave Analysis (RCWA). Modal allocation for each resonance in the GMR structure is performed using the four-layer waveguide. The measured super-mode resonance has shown sensitivity enhancement almost three folds of that of the traditional guide mode resonance. Also, this realization occurs in a broad dynamic range through optimization of the structure’s parameters guarantees usage in multiple sensing applications. In the second part, the study demonstrates design and development of an open-source platform-based reflection spectroscopy readout system for guided mode resonance sensing applications. The GMR dimensions, reflection grating period, imaging system and components orientation are optimized to enhance the angular resolution while sustaining resonance excitation within the visible range. To achieve the needed arrangement of the multiple components, 3D printing is utilized to build the mechanical mounting. The reflection spectra are extracted from the webcam images and processed using software written on raspberry-pi computational unit. This ensures the compactness and portability of the system. The system performance of the transducer is tested by measuring the changes in the refractive index of the environment at the GMR chip interface.