Abstract
Detection of low-index materials such as aerogels and also detection of refractive index variations in these materials is still a challenging task. Here, a high figure of merit (FOM) sensor based on plasmon-induced transparency (PIT) is proposed for the detection of aerogel refractive index changes. In the proposed PIT sensor, the transparency window in an opaque region arises from the coupling between surface plasmon polariton (SPP) mode and planar waveguide mode. By comprising sub-wavelength grating (SWG) in the planar waveguide region, the maximum of the electric field of waveguide occurs in a low index media. This facilitates detection of the aerogels when they are used as the low index material (sensing material). Application of the subwavelength grating waveguide also improves the sensitivity of the sensor by a factor of six compared to a conventional structure with a homogenous waveguide. The proposed structure has a quality factor of Q ≥ 1800, and a reflection of 86%, and can detect the refractive index changes as low as Δn = 0.002 (around n = 1.0). The lineshape, Q-factor, and resonant wavelength of the transparency spectrum can be controlled by tailoring the structural parameters. Our work also has potential application in switching, filtering, and spectral shaping.
Highlights
Detection of low-index materials such as aerogels and detection of refractive index variations in these materials is still a challenging task
In plasmoninduced transparency (PIT), broad low-quality resonance is provided by surface plasmon polariton (SPP) mode at the metal–dielectric interface, and a dielectric waveguide mode is responsible for realizing a narrow high-quality resonance[7,8]
Planar waveguide-coupled SPP structures have been widely used as promising candidates for realizing P IT24,25
Summary
Detection of low-index materials such as aerogels and detection of refractive index variations in these materials is still a challenging task. The sensitivity and resolution of conventional plasmonic sensors are limited by inherent optical loss of the metals which results in wideband SPP resonance. To address this drawback, a variety of solutions have been proposed to obtain narrow linewidth resonances. Planar waveguide-coupled SPP structures have been widely used as promising candidates for realizing P IT24,25 In these structures, the field of the narrow spectrum mode (dark mode) is mainly confined in a dielectric media. This limitation cannot be completely mitigated, the Q-factor and sensitivity of the PIT sensors can be improved in the design process as it is done in the following
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