All-dielectric metasurfaces are unique component to control optical wavefront with high transmission or reflection coefficient. Recently, accelerating beam, which propagates along curved arbitrary trajectories, has been realized with conventional diffractive optical elements (DOE). However, DOE suffer from low sampling ratio of rapid phase gradients and its diffraction efficiency drops quickly when the wavelength is switched to another wavelength which is different than the designed wavelength.. In this study, we show accelerating beam which is generated by highly efficient and polarization insensitive all-dielectric metasurfaces in the visible wavelength. The acceleration beam is numerically generated with the proposed metasurfaces which are composed of TiO2 nanopillars residing on glass substrate using finite difference time-domain computational method. It is shown that this beam has the ability to propagate curved trajectories in air medium. Transmission efficiency of the proposed structure is above 65% and desired arbitrary trajectories have been achieved. Generating highly efficient accelerating beam can be used in photonic applications in optical imaging, spectroscopy, optical micromanipulation and nonlinear optics.
In modern optic and photonic applications, tunability of the asymmetric transmission has become important due to its adjustable unidirectional transmission. In this study, we design a three-dimensional trapezoidal metallic nano structure on a stretchable substrate. It shows broadband tunable asymmetric light transmission in the visible spectrum. The proposed structure is made of a periodic nano array of a trapezoidal shaped aluminum on a stretchable substrate. The transmission properties of the proposed structure with respect to the geometric parameters were systematically investigated employing finite-difference time-domain computations. It was shown that the intensity and the bandwidth of the asymmetric light transmission between 400 nm and 800 nm wavelengths change when the flexible substrate is stretched. The period of the designed structure varies depending on the stretch of the substrate. For example, when the substrate is stretched, the period of the structure is 450 nm and when it is unstretched, the period is 350 nm. This increase in the period causes a red shift in the wavelength range of the asymmetric transmission. While the asymmetric transmission under unstretched case starts at 350 nm and stops at 514.5 nm, under stretched case it starts at 450 nm and stops at 661.5 nm. In addition, the performance of our structure is insensitive the polarization of the incoming radiation in both forward and backward illumination directions. This study provides a path toward the realization of tunable optical devices for the applications which require dynamic tunability.
In this study, we propose a new approach for controlling reflection of light by using highly efficient and polarization insensitive all-dielectric metasurfaces. Moreover, we applied our model on the planar silicon solar cell to manage light trapping. For the inital design, TiO2 nano-pillars with single diameter is arranged on the silicon substrate. However, single diameter nano pillars is not enough to reducereflection covering all solar spectrum. To induce reflection reduction over the entire visible spectrum, we include different pillars with varying diameters.. The reflection of final structure with three rods is lower than 17% at 400-1000 nm. Numerical results show that the short circuit current and solar cell efficiency has been enhanced by factors of 1.66 and 1.62 compared to planar basic solar cell. The presented method allows to improve absorbing efficiency of solar cell via reducing reflection and enhancing light trapping.
Focal plane arrays (FPAs) as a two-dimensional detector pixel matrix positioned in the focal plane of an optical system have been developed continuously for obtaining higher resolution. On the other hand, for developing highresolution, compact-size FPAs, used methods such as the miniaturization of pixel size leads to serious problems such as increased optical crosstalk. In this study, we proposed highly efficient all-dielectric metasurface lens arraybased FPA at mid-wave infrared spectrum. All-dielectric metasurface lens arrays were numerically demonstrated to achieve high optical efficiency above 85%. Moreover, our design compared with conventional and earlier metasurface-based studies has exhibited much superior optical crosstalk performance. While standing the high efficiency, optical crosstalk is decreased to low level of ≤ 2.8%. A figure-of-merit (FoM) is also defined for the device performance, which is designated as the focusing efficiency per optical crosstalk times the f-number. The results show that a FOM of approximately 90 is achieved. These proposed all-dielectric metasurface lens arrays demonstrate great potential for increasing the signal to noise ratio and sensitivity thus paving the way for compactsize and high-resolution FPAs to be deployed in various applications including thermal cameras, imaging devices and bolometers.
Intensive researches in the area of metasurfaces have provided a new insight to obtain flat and compact optical systems.
In this letter, we numerically show that, highly efficient tunable beam steering effect in transmission mode is achieved at
wavelength λ = 550 nm using nematic liquid crystals (LCs) infiltrated into double sided metasurfaces. Using the electrooptical
feature of LCs, the phase profile of the metasurfaces is controlled and thus, the transmitted beam is deflected
within the range from -15° to 15° steering angles. Transparent dielectric materials are used in the designed structure that
provides highly efficient beam-steering; the corresponding transmission efficiency is above 83% in the visible spectrum,
which is another superiority of the proposed hybrid tunable structure over present plasmonic/metamaterial approaches.
The designed metasurface still preserves its beam deflection property covering the visible spectrum and hence, such
hybrid structure can be implemented for broadband electro-optically controllable beam steering applications.