In this paper, we propose a two-dimensional metal-dielectric grating with dielectric nanodisks on a thin gold film structure for refractive index sensing due to its near unity absorption at 1050 nm wavelength. The perfect absorption mainly originates from excitation of the horizontal magnetic dipole mode in the metal-dielectric structure. The results show that the sensitivity and full width half maximum are 560 nm/RIU and 11.13 nm over the sensing range of 1.33 to 1.38, respectively. Obviously, the corresponding figure of merit is calculated to be 50.3 RIU-1, which shows a high sensing performance. Moreover, it also shows excellent performance by measuring the light intensity change in the reflected light at a certain wavelength. The proposed structure has great potential application in biological sensing, integrated photodetectors, chemical applications and so on.
A 1×5 transmission grating splitter with triangular structure under normal incidence at the wavelength of 1550 nm is presented in this paper. In order to further increase the efficiency, the material of the designed grating is MgF2. The whole transmitted diffraction efficiency of the gratings is over 99% with uniformity better than 0.3%. The designed parameters of this triangular grating are employed by the rigorous coupled-wave analysis and the simulated annealing algorithm. This grating has a large tolerance for fabrication with better performance, which should be highly interesting for practical applications.
As an important means to obtain three-dimensional depth information of target, optical measurement has been widely used in face recognition, machine manufacturing, aerospace and other related fields in the past decades. Optical three-dimensional imaging and depth measurement is a fast and non-contact method for reconstructing three-dimensional imaging and depth measurement of objects based on optical means and digital image processing analysis. In this paper, a three-dimensional measurement module of transversely rotating combined Dammann grating is proposed, which generates interleaved high-density dot-matrix structured light for three-dimensional imaging and measurement. The measurement module consists of integrated components of laser and beam expander, collimating lens, four transversely rotating combined Dammann gratings with different beam splitting ratios, and objective lens. The laser emits a laser beam which is collimated by a collimating lens. Four Dammann gratings are used to generate four non-staggered dot-matrix by splitting them, and then the high-density staggered projection dot-matrix for three-dimensional measurement and imaging are projected by the objective lens. The measurement module has the advantages of simple structure, high output dot-matrix density, staggered projection dot-matrix edges, and easy integration into mobile devices. This technology may reduce the complexity, number of optical elements, power consumption and cost of structured light projectors in mobile and fixed 3D sensors.
In this paper, we propose a two-dimensional (2-D) triangular lattice photonic crystal plate by close-packed SiO2/ TiO2 layers with the stacking mode of ABABABA. By using the finite-difference time-domain (FDTD) method, negative refraction of a single Gaussian beam incident plate with different angles are respectively demonstrated; clear image spots of a point source with normalized frequency ω=0.3605(2πc/a) vertical incident media plate are obtained in the image plane. It can be found that the imaging properties are as same as the isotropic homogeneous medium with refractive index n=-1. The measurement results show that when the distance between the image and the upper surface of the sample V is 5.12a, 3.09a and 1.15a, the distance between the source and the lower surface of the sample U is a, 3a and 5a, respectively. This means that the sum of U and V is mostly equal to the thickness of the plate L and the negative effect of near-perfect lens is realized. This proposed structure with negative refraction properties may have great applications for the design of photonic crystal focusing devices.
In this paper, we theoretically demonstrate a polarizing filter consisted of graphene ribbon arrays with varying width placed on the top surface of dielectric and a metal reflector rested at the bottom of the structure. It is found that proper ribbon width, which corresponds to resonant frequency of graphene plasmons, is a crucial factor that can significantly influence the absorption effect. The results of fullwave numerical simulations indicate that total absorption of more than 90% for TE polarization and approaching to 1% for TM polarization can be achieved at normal incidence in the infrared range. Therefore, this characteristic can be applied into polarizing filter by adjusting the coupling effect between the graphene ribbon arrays. Such structure will be beneficial to the manufacture of infrared nano-photonic devices for optical filtering and selective absorption.