Sensitivity Enhancement Using Different Design Configurations for Photonic Crystal Waveguide Applications

Abstract

In this work, three types of sensors have been designed. In the first type, a ring shaped photonic crystal waveguide is designed using finite difference time domain method. This waveguide can be used for gas sensing applications. After introducing the line defect, transmission spectra was obtained with different hole diameters. With the increase in hole diameter, the sensitivity increases. Further enhancement in sensitivity was measured by etching in silicon guiding layer and up to a certain depth in the buried oxide layer. It was observed that the sensitivity increases up to certain etch depth after which it is found to be decreasing. After this, infiltration with different gaseous analytes was done to measure the sensitivity based on the shift in the cut off wavelength as observed because of the change in refractive index of the structure. The experimental results showed that the ring shaped structure had a sensitivity value of 675nm/RIU. This sensor can be used to sense different gases like hydrogen, ammonia, nitrogen etc. In the second type, a 2-D photonic crystal waveguide based biosensor is designed with a diamond shaped ring resonator and two waveguides-a bus waveguide and a drop waveguide. The sensing mechanism is based on change in refractive index of the analytes as explained above leading to a shift in the peak resonant wavelength. This mechanism can be used in the field of bio-medical treatment where different body fluids such as blood, tears, saliva or urine can be used as the analyte in which different components of the fluid can be detected. It can also be used to differentiate between the cell lines of a normal and an unhealthy human being. Average value of quality factor for this device comes out to be 1082.2063. Sensitivity values increases wi th the increase in RI. For 0.02 change in RI, sensitivity increases by 0.0154nm/RIU. Finally we design three dimensional (3-D) photonic crystal waveguides using group III-V semiconductor materials and study the effect of different directions of light propagation for each of these materials. The presence of photonic band gaps (PBG’s) in photonic crystals can be used to control the direction of propagation of light by iv prohibiting light flow at a certain frequency range in certain directions. Semiconductor materials posses a forbidden energy gap between valence band and conduction band of electrons. Thus, an analogy can be drawn between the behaviour of electrons in case of semiconductors and that of light in case of photonic crystals. Silicon based waveguide is first designed and then integrated with different group IIIV semiconductors. The sensitivity values are calculated and compared for each of these materials with respect to silicon based waveguides. The designed structure consists of holes filled with water in a silicon/silicon and semiconductor configuration and the refractive index is varied from 1.33 to 1.45. Corresponding shift in peak wavelength is measured and the sensitivity values are calculated for the same. Among all the materials, Indium phospide seems to be the most appropriate choice based on the light transmission with an average sensitivity of 201.76 nm/RIU obtained by infiltration of holes with various analytes.