Ultrahigh Q-Factor and Ultrasensitive Refractive Index Sensor Based on a Multiple-Slot Photonic Crystal Cavity

Abstract

A novel design of multiple-slotted 1-D photonic crystal nanobeam cavity has been proposed in this article. The design utilizes the benefits of high optical density offered by the narrow slots as well as improved light–matter interaction and, thereby, sensitivity due to the multiple slots. Different design parameters, such as width, separation, and number of slots, and number and sizes of holes, are optimized for achieving better quality factor (QF) and sensitivity simultaneously. A QF and sensitivity using two or three number of slots have been found in the order of $3.2\times 10^{7}$ and 1016 nm/refractive index unit (RIU) or $1.26\times 10^{7}$ and 1049 nm/RIU, respectively. Tolerance of the design for possible random fabrication imperfections has also been evaluated. It depicts that the structure is tolerant up to 20-nm random deviations, with low impact to sensitivity, albeit at a moderate cost to the QF for deviations above 10 nm. Finally, the optimized design has been used in a theoretical study for analyzing the applicability of the sensor in assessing glucose levels in human urine samples. The theoretical results suggest that the proposed design can be utilized for realizing efficient industrial and bimolecular sensors.