The advancement of fabrication techniques, especially in the field of polymer-based photonic devices, has led to the implementation of novel designs with increased flexibility. In this paper, we propose a polymer-based whispering gallery spiral waveguide, which has been tapered down to nano-dimension for the detection of gold nanoparticles. Gold nanoparticles are being explored extensively in the areas of catalysis, imaging, therapeutic agents, drug delivery in various chemical and medical applications. Though, detection of gold nanoparticles in low concentration with high sensitivity is still a challenge. The proposed structure can be used to detect a single gold nanoparticle. It consists of two interleaved spirals; the inner ends of the spirals are connected by semicircular-arcs of a circle forming an S-shaped structure whereas the outer ends of the spirals serve as input and output ports of the waveguide. By nano-tapering, the center of the spiral, we observe enhanced evanescent field in the tapered region. The interaction of the evanescent field with the gold nanoparticle causes a shift in the characteristic wavelength of the device. The capability of the device to detect gold nanoparticle of different radius (10 nm-100 nm) has been theoretically analyzed. As the shift in the characteristic wavelength depends on the size of the gold nanoparticle, it provides a size selective detection of nanoparticles and this is regarded as an extrinsic size effect. The proposed device has been fabricated by two-photon polymerization based direct laser writing technique.
Tamm plasmon polaritons (TPPs) are excellent candidates for photonic device application for their intriguing properties and simple fabrication design. In this study, optical Tamm structures are fabricated by depositing silver thin film on onedimensional photonic crystals (1DPhCs), constituting twelve pairs of alternating quarter wave thick SiO2 and TiO2 thin films. Carbon quantum dots (CQDs) were incorporated in the TiO2 matrix of the final four pairs of the 1DPhCs. TPPs are observed in the reflectance spectra of the samples with and without CQDs. With the help of transfer matrix method electric field intensity distribution profile is obtained. It is observed that the electric field is confined and enhanced at the metal-1DPhC interface and decays within the 1DPhC. Comparison of PL emission from samples with and without CQDs in the last four layers are presented. Enhanced PL emission from CQDs corresponding to the TPP mode and suppression of emission within the photonic stop band is demonstrated.
Here, we present the design and fabrication details of a metal grating-one dimensional photonic crystal (1DPhC) structure that can efficiently couple the normal incident light into the 1DPhCs. We implement this by designing a silver (Ag) nano-grating on the 1DPhC which consists of 10 bilayers of SiO2/TiO2 thin films on a silicon substrate. Ag coated 1DPhC shows a sharp dip in the reflectivity within the photonic stop band, which is a distinct signature of the excitation of Tamm states at the interface of metal-1DPhC boundary. Reflection spectrum of Ag grating–1DPhC structure shows that the Tamm state is modified in the presence of the Ag grating, giving rise to a surface state in the vicinity of the Tamm resonance. The experimental results obtained are well supported by simulations which provide the field distributions for the Tamm resonance and the surface state.
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