Highly localized electromagnetic field distributions near the "shadow-side" surface of certain transparent mesoscale bodies illuminated by light waves are called photonic jets. We demonstrated formation of three-dimensional (3D) tunable photonic jets in terahertz regime (terajets, TJs) by dielectric micro-objects -including spheres, cylinders, and cubes-coated with a bulk Dirac semimetal (BDS) layer, under uniform beam illumination. The optical characteristics of the produced TJs can be modulated dynamically through tuning the BDS layer's index of refraction via changing its Fermi energy. It is demonstrated that the Fermi energy of BDS layer has a significant impact on tuning the optical characteristics of the produced photonic jets for both TE and TM polarizations. A notable polarization dependency of the characteristics of the TJs was also observed. The impact of obliquity of the incident beam was studied as well and it was demonstrated that electromagnetic field distributions corresponding to asymmetric photonic jets can be formed in which the intensity at the focal region is preserved in a wide angular range which could find potential application in scanning devices. It was found that the maximum intensity of the TJ occurs at a non-trivial morphology-dependent source-angle.

In this paper, we theoretically investigate the transmission properties of a structure composed of a topological one-dimensional photonic crystal (1D PhC) heterostructure and a conventional 1D PhC containing indium-antimonide (InSb) as a defect layer using the transfer matrix method. The phenomenon of Fano resonance can be achieved by coupling the defect mode with the topological edge state mode, which is supported by the topological PhC. The numerical results show that a narrow Fano resonance is observed in the transmission spectrum of the structure in the presence of the external magnetic field applied to the InSb defect layer. The optical properties of the InSb defect layer, and, therefore, the Fano resonance, can be dynamically controlled by changing the applied external magnetic field. The results obtained with the proposed structure reveal that the magnetic field has the greatest influence on controlling the optical properties of the Fano resonance. These findings could be beneficial for optical devices such as optical filters, sensors, and optical switches.

In this study, the photonic band structure of two-dimensional photonic crystals with square and honeycomb lattices consisting of air holes in the Kerr nonlinear material background has been investigated. We assumed that the holes with different geometrical shapes are filled with plasma. The numerical results based on the finite difference time method show that most of the designed structures represent a complete photonic bandgap with noticeable width at optimum values of structural parameters for low-intensity incident waves, in which the width can be changed through varying the incident light intensity. The calculations show that when the shape of the plasma-filled holes is the same as the shape of the unit cell of the structures, the most change in the total photonic bandgap is visible in the frequency range as the light intensity of the incident light changes. Furthermore, the maximum width of the photonic gap in these structures was reached , which has increased approximately in comparison with similar previously studied structures. The obtained result can be used for designing tunable optical devices.

We have theoretically investigated the nonreciprocal surface states created at the interface between the semiinfinite one-dimensional magneto-optic photonic crystal in Voigt configuration and air in the presence of monolayer graphene as a cap layer, using the transfer matrix method. The modification of surface states was studied by changing the Fermi energy of the graphene sheet. The results indicate that the nonreciprocality of surface states could be effectively controlled by Fermi energy. We also analyzed the effect of the termination layer of photonic crystal on surface states and found that the arrangement with termination layer of magnetized semiconductor supports unidirectional surface states.

In this paper, photonic nanojets are achieved using circular and elliptical dielectric cylinders in air background. Therefore, for obtaining high intensity and large focal length photonic nanojets, using highresolution finite difference time domain method, the optical properties of obtained nanojets are studied for all possible geometrical parameters. Numerical results show that the field intensity of circular photonic nanojet is higher than the elliptical one, while the focal length of elliptical photonic nanojet is greater than that of circular one. These results can be helpful in designing advanced photonic components such as ultra-sensitive particle sensors.

We proposed a new method for designing graded index lens using liquid crystal infiltration into annular photonic crystals. Applying an external nonuniform voltage in the transverse direction perpendicular to the direction of light propagation yields different orientation of liquid crystal molecules inside the photonic crystal unit cells. As a result, a gradient refractive index was modulated. We numerically investigate focusing properties of the designed graded index structure using plane-wave expansion and finite-difference time-domain methods. The gradient refractive index profile was adjusted by varying the nonuniform voltage excitations, which consequently altered the focal distance of the graded index structure. A wide tuning range of 1856 nm was achieved for focal distance by the proposed graded index structure. This feature can be implemented for planning a flat lens with tunable focal distance based on electro-optic effect. These achievements may have future applications in some optical devices such as near-field imaging and scanning.

In this paper, a thin film silicon solar cell with anti-reflection coatings on front surface and the combination of periodic grating and photonic crystal on its back surface has been considered. The thickness and number of anti-reflection coatings, as well as the geometric and physical parameters of photonic crystal and grating are optimized to increase the optical absorption of solar cell. The simulations have been performed using the finite difference time domain method with Lumercial software. The results show that the optical absorption of solar cell has been increased significantly by utilizing the anti-reflection coatings, photonic crystal and grating.

An adaptive graded index photonic crystal (GRIN PC) lens system is designed by using liquid crystal (LC) infiltration. LCs have the property to change their refractive indices when an external voltage is applied. This feature allows for the modulation on the effective index profile of the low-index contrast GRIN PC lens. Alongside this property, without changing the length of the designed 2D GRIN PC, the corresponding focal distance can be adapted from infinity to a certain positive or negative focal point by controlling the applied voltage. The effects of random perturbations and intentional line defects on the focal tuning capability of proposed 2D GRIN PC are also studied. Moreover, due to the scalability of PC's dispersion relations, the sizes of the proposed devices can be adapted so that it may operate in either infrared or microwave regimes. Consequently, the proposed tunable polymeric GRIN PC can be implemented in various optical applications, such as near-field imaging and scanning systems, vision correction, and auto-focusing.

Using the Dirichlet-to-Neumann map method, we have calculated the photonic band structure of two-dimensional metallodielectric photonic crystals having the square and triangular lattices of circular metal rods in a dielectric background. We have selected the transverse electric mode of electromagnetic waves, and the resulting band structures showed the existence of photonic bandgap in these structures. We theoretically study the effect of background dielectric on the photonic bandgap.

We investigate numerically optical bistability in direct-coupled cavity-waveguide photonic crystal system using the finite-difference time-domain method. The quality factor of the cavity is optimized by engineering the geometrical parameters. Numerical results indicate that the threshold power of optical bistability can be reduced greatly due to the increased quality factor.

In this paper, we theoretically study the electromagnetic surface waves localized at the interface between a homogeneous dielectric medium and a semi-infinite, one-dimensional photonic crystal (1D PC). The semi-infinite 1D PC is made of alternative layers of right-handed (RH) and dispersive left-handed (LH) materials in the presence of a liquid crystal (LC) cap layer. In this structure, we derive the surface waves dispersion relation with tunable switching and localization by using an analytical direct matching procedure within the Kronig-Penny model. It is shown that, for both of layer arrangements, the variation of molecules orientation of the LC cap layer acts as an effective tool to tune the type (tuned switching) and localization of the surface waves and it also can create a surface mode with maximum localization in the first frequency bandgap.