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Register a new userAll Dielectric Biaxial Metamaterial: A New Route to Lossless Dyakonov Waves with Higher Angular Existence Domain
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Authors
Ayed Al Sayem
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In this article, we propose and numerically analyze an all dielectric biaxial metamaterial [ADBM] constructed by multilayer pattering of a sub-wavelength ridge array of Silicon and a flat SiO2 layer. The proposed ADBM can support Dyakonov Surface Waves [DSWs] with infinite propagation length which can propagate in a wide angular domain. Though natural uniaxial and biaxial materials and also nanowire all dielectric metamaterials can also support DSWs, the angular existence domain [AED] is limited to a very narrow range. Our proposed ADBM can support can overcome this limitation and it can achieve higher AED than any all dielectric structures reported in literature till date. Our proposed ADBM can be easily fabricated by the current fabrication technology. Due to its lossless nature, it may find substantial applications in optical sensing, optical interconnects, wave-guiding, solar energy harvesting etc.
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The propagation of Dyakonov surface waves (DSWs) at the planar interface between an isotropic material and a linear electro-optic birefringent material can be dynamically controlled using the Pockels effect. The range of directions for DSW propagation has been previously found to be rather narrow. By careful choice of various parameters, this range of directions can be increased by more than an order of magnitude.
In this article, it has been theoretically shown that broad angle negative refraction is possible with asymmetric anisotropic metamaterials constructed by only dielectrics or loss less semiconductors at the telecommunication and relative wavelength range. Though natural uniaxial materials can exhibit negative refraction, the maximum angle of negative refraction and critical incident angle lie in a very narrow range. This notable problem can be overcome by our proposed structure. In our structures, negative refraction originates from the highly asymmetric elliptical iso-frequency.This is artificially created by the rotated multilayer sub-wavelength dielectric/semiconductor stack, which act as an effective asymmetric anisotropic metamaterial.This negative refraction is achieved without using any negative permittivity materials such as metals. As we are using simple dielectrics, fabrication of such structures would be less complex than that of the metal based metamaterials. Our proposed ideas have been validated numerically and also by the full wave simulations considering both the effective medium approach and realistic structure model. This device might find some important applications in photonics and optoelectronics.
In this article, a 2D plasmonic waveguide loaded with all dielectric anisotropic metamaterial, consisting of alternative layers of Si-SiO2, has been theoretically proposed and numerically analyzed. Main characteristics of waveguide i.e. propagation constant, propagation length and normalized mode area have been calculated for different values of ridge width and height at telecommunication wavelength. The respective 1D structure of the waveguide has been analytically solved for the anisotropic ridge as a single uniaxial medium with dielectric tensor defined by Effective Medium Theory (EMT). The 2D structure has been analyzed numerically through FEM simulation using Mode analysis module in Comsol Multiphysics. Both the EMT and real multilayer structure have been considered in numerical simulations. Such structure with all dielectric metamaterial provides an extra degree of freedom namely fill factor, fraction of Si layer in a Si-SiO2 unit cell, to tune the propagation characteristics compared to the conventional DLSSP waveguide. A wide range of variations in all the characteristics have been observed for different fill factor values. Besides, the effect of the first interface layer has also been considered. Though all dielectric metamaterial has already been utilized in photonic waveguide as cladding, the implementation in plasmonic waveguide has not been investigated yet to our best knowledge. The proposed device might be a potential in deep sub-wavelength optics, PIC and optoelectronics.
Photonic crystals have been demonstrated as a versatile platform for the study of topological phenomena. The recent discovery of higher order topological insulators introduces new aspects of topological photonic crystals which are yet to be explored. Here, we propose a dielectric photonic crystal with unconventional higher order band topology. Besides the conventional spectral features of gapped edge states and in gap corner states, topological band theory predicts that the corner boundary of the higher-order topological insulator hosts a 2/3 fractional charge. We demonstrate that in the photonic crystal such a fractional charge can be verified from the local density of states of photons, through the concept of local spectral charge as an analog of the local electric charge due to band filling anomaly in electronic systems. Furthermore, we show that by introducing a disclination in the proposed photonic crystal, localized states and a 2/3 fractional spectral charge emerge around the disclination core, as the manifestation of the bulk disclination correspondence. The predicted effects can be readily observed in the state-of-the-art experiments and may lead to potential applications in integrated and quantum photonics.
Micro-sized spheres can focus light into subwavelength spatial domains: a phenomena called photonic nanojet. Even though well studied in three-dimensional (3D) configurations, only a few attempts have been reported to observe similar phenomena in two-dimensional (2D) systems. This, however, is important to take advantage of photonic nanojets in integrated optical systems. Usually, surface plasmon polaritons are suggested for this purpose, but they suffer notoriously from the rather low propagation lengths due to intrinsic absorption. Here, we solve this problem and explore, theoretically, numerically, and experimentally, the use of Bloch surface waves sustained by a suitably structured all-dielectric media to enable subwavelength focusing in an integrated planar optical system. Since only a low index contrast can be achieved while relying on Bloch surface waves, we perceive a new functional element that allows a tight focusing and the observation of a photonic nanojet on top of the surface. We experimentally demonstrate a spot size of 0.66{lambda} in the effective medium. Our approach paves the way to 2D all-dielectric photonic chips for nano-particle manipulation in fluidic devices and sensing applications.
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