High sensitivity of sensors based on two-dimensional photonic crystal

Photonic crystals (PCs) have achieved a lot of research significance due to their projected applications. Their use as sensors is enabled due to their well-defined physical properties such as reflectance/ transmittance, superior levels of sensitivity resulting in precise detection limits. In this paper, we propose an ultracompact RI (refractive index) sensor based on single line photonic crystal waveguide structure. The properties of the sensor are simulated using the finite-difference time-domain (FDTD) method. The transmission spectrums of the sensor with different ambient refractive indices are calculated. The calculation results show that a change in ambient RI is apparent; the sensitivity of the sensor is achieved. The radius of the air holes localized at each side of the line defect is optimized to realize high sensitivity, wide measurement range and improved transmission. Development of sensor designs that enhance sensitivity is especially important because it allows detection of lower concentrations of analytes. For instance, refractive index (RI) sensing techniques detect an analyte by a local refractive index shift.

I. INTRODUCTION

Recently, there has been growing interest in photonic crystals (PCs) [1] which are periodic dielectric structures at the optical wavelength scale because it produces a certain frequency region, where the propagation of electromagnetic wave is forbidden, so-called photonic band gap [2]. This property of PCs provides the ability to control and confine the light propagation. This photonic bandgap is a function of the refractive index (RI) modulation which defines the crystal. While most RI sensing approaches rely on the interaction between a weak evanescent wave and the analyte, photonic crystals allow strong light confinement to the sensing region, potentially even primarily within the analyte itself.