Abstract
Sensing abilities of a one-dimensional photonic crystal (1DPhC) represented by a multilayer dielectric structure are analyzed theoretically and experimentally, using a new wavelength interrogation interference method. The structure comprising a glass substrate and six bilayers of TiO2/SiO2 with a termination layer of TiO2 is employed in both gas sensing based on the Bloch surface wave (BSW) resonance and liquid analyte sensing based on a self-referenced guide-mode resonance (GMR). We model the spectral interference reflectance responses in the Kretschmann configuration with a coupling prism made of BK7 glass and show that a sharp dip with maximum depth associated with the BSW excitation is red-shifted as the refractive index (RI) changes in a range of 1-1.005. Thus, a sensitivity of 1456 nm per RI unit (RIU) and figure of merit (FOM) of 91 RIU-1 are reached. Similarly, we model the responses for aqueous solutions of ethanol to show that dips of maximum depth are associated with the GMRs, and the highest sensitivity and FOM reached are 751 nm/RIU and 25 RIU-1, respectively. Moreover, we show that one of the dips is with the smallest shift as the RI changes, and hence it can be used as a reference. The theoretical results are confirmed by the experimental ones when the BSW resonance is used in sensing of humid air with a sensitivity of 0.027 nm/%relative humidity (RH) and FOM of 1.4×10-3 %RH-1. Similarly, the GMR is used in sensing of aqueous solutions of ethanol, and the highest sensitivity and FOM reached 682 nm/RIU and 23 RIU-1, respectively. The reference dip is also resolved and this self-reference makes the measurement more accurate and repeatable, and less sensitive to optomechanical drifts.
Highlights
IntroductionBragg mirrors or one-dimensional photonic crystals (1DPhCs), as realizations of complex dielectric structures [1], have a huge impact on research of numerous topics and applications, such as omnidirectional reflectors [2], polarization selectors [3], narrowband optical filters using omnidirectional photonic band gaps (OPBGs) [4], and especially sensors utilizing Bloch surface waves (BSWs) [5,6,7,8,9,10,11,12,13,14,15,16]
The resonance wavelength, determined with a precision of 0.01 nm using a zero-crossing in the first derivative of the reflectance ratio, is shown in Fig. 10(b) as a function of the relative humidity (RH) of air and this dependence is well approximated by a linear function
For a 1DPhC comprising a glass substrate and six bilayers of TiO2/SiO2 with a termination layer of TiO2 gas sensing ability based on the Bloch surface wave (BSW) resonance has been revealed
Summary
Bragg mirrors or one-dimensional photonic crystals (1DPhCs), as realizations of complex dielectric structures [1], have a huge impact on research of numerous topics and applications, such as omnidirectional reflectors [2], polarization selectors [3], narrowband optical filters using omnidirectional photonic band gaps (OPBGs) [4], and especially sensors utilizing Bloch surface waves (BSWs) [5,6,7,8,9,10,11,12,13,14,15,16]. BSWs can be excited by both s- and p-polarized waves [22] at any wavelength, including near- and mid-infrared region [16,23], by suitably changing the geometry and materials of the photonic crystal. Tamm plasmon (TP) based sensors utilizing a type of surface waves at the interface between a metal and a 1DPhCs have been studied [32], and a direct excitation from free space and excitation by both s- and p-polarized waves have been utilized [33,34,35]
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