Design and Analysis of Integrated Optic Waveguide Grating for Sensor and Communication Applications

Abstract

Waveguide gratings are widely being used for multitude of applications owing to high sensitivity, immunity to electromagnetic interference, multiplexing capabilities, light weight and compactness. Waveguide gratings on Silicon-on-Insulator (SOI) platform have been attracting interest for optical communication and sensing applications. SOI platform has several advantages over other materials like Lithium Niobate, Polycarbonate, Silicon Nitride etc. High index contrast of SOI leads to miniaturization of the chip. But to design ultra low cost devices, SOI is not the suitable platform. Plastic or polycarbonate might be a possible alternative to silicon for low cost or disposable sensors. In this thesis, we have designed and analysed various structures of waveguide gratings on the basis of their suitability for communication and sensing applications. Mathematical models have been developed for various structures and analysed using simulations. Waveguide diffraction grating has been used as a grating coupler for fiber to integrated optic (IO) coupling. Fabrication and characterization of waveguide grating is also carried out. Waveguide Bragg gratings are useful in optical MEMS sensor applications. Here waveguide Bragg grating (WBG) based pressure and acceleration sensors are studied. Diaphragm and cantilever beam, mechanical structures have been used for pressure and acceleration measurements respectively. These mechanical structures are designed to enhance the sensitivity of sensors. Opto-mechanical coupling is analyzed through photo-elastic effect. A new design of surface relief waveguide Bragg grating configuration called superstructure WBG is proposed to eliminate the cross-sensitivity of the sensor due to external factors like temperature. A theoretical analysis has been provided for the superstructure WBG configuration. The sensitivity measurement for pressure and acceleration is found to be 0.21 pm/Pa and 6.49 nm/g respectively. The superstructure configuration is also used for multiparametric sensor designs. Multiple parameters like pressure and acceleration have been measured simultaneously using monolithic, multiparametric sensor using superstructure WBG. Finally a novel differential pressure sensor is proposed using surface relief WBGs embedded in a Mach Zehnder interferometer (MZI) and theoretically designed and analysed. The differential pressure sensor sensitivity of 0.2 pm/Pa has been achieved. Guided mode resonance grating filters are used for biosensing applications. The change in effective refractive index leads to two types of biosensing namely, the homogeneous sensing and surface sensing. In homogeneous sensing, the effective refractive index of a propagating optical mode changes with uniformly distributed sample extending over a distance well exceeding the evanescent field penetration depth. Here the sample serves as the waveguide cover. Where as in surface sensing, the sample adsorbs onto the surface of the waveguide and in this case, the effective refractive index of an optical mode changes with the refractive index as well as the thickness of a sample. Both sensing schemes have been analysed to detect concentration of sugar, the analyte in honey being the sample. The sensitivity of 142 nm/RIU and 23 nm/RIU for homogeneous and surface sensing respectively are found. WBG is also useful in filtering applications. We have designed WBG with periodic perturbation to get multiple wavelengths filter response.