Controlling the self-collimation characteristics of a near-infrared two-dimensional metallic photonic crystal

Self-collimation characteristics of the two-dimensional square-lattice photonic crystal （PC） consisting of metal rods immersed in silicon are studied by the finite-difference time-domain method. The Drude dispersion model is adopted to describe the metal rod, and the self-collimation behaviours of the near-infrared light through the PC are studied. The frequency region and the tolerance of incident angle for the self-collimation behaviour can be controlled by changing the shape of the metal rods.

Self-Collimation for Two-Dimensional Micro-Angle Measurement in Space

How to measure the two-dimensional attitude angle of space target and achieve stable tracking and aiming has become an important problem. The self-collimation is often measured via one-dimensional motion of the object in space. This paper proposes a micro-angle measurement system based on self-collimation to obtain the two-dimensional angle information of moving objects in space, and a thrice reflecting optical path structure is built to improve the compactness of the system. First, by establishing a posture angle measurement and decomposition model, the two-dimensional deflection angle value of the reflecting mirror is derived from the rotation angle equation;Second, the self-collimating measurement process is simulated to show the relationship between the reflecting mirror rotation angle and the imaging spot distortion of detector;Third, a two-dimensional micro-angle experimental platform is established based on the Position Sensitive Detector(PSD). Finally, nonlinear error of PSD is improved by the cubic spline interpolation method. The case results show a 15% reduction in the angle error.

Self-collimation in photonic crystals with anisotropic constituents

In a photonic crystal composed of anisotropic constituents we quantify the range of input angles and the degree of collimation of the beam inside the crystal. The optical properties of a photobleached 4- dimethylamino-N-methyl-4-stilbazolium-tosylate （DAST） crystal are used in our model to demonstrate the efficacy of the self-collimation features.

Applications of Self-Collimated Properties of Photonic Crystal in 3D Imaging Lidar System

Photonic crystals （PCs） are increasingly attracting attention due to their ability to control light propagation.In this paper,the dispersion properties of a two-dimensional （2D） square lattice PCs with plane- wave expansion （PWE） method are presented,the equi-frequency contours and the band structure are analyzed,and the alignment transmission characteristics are simulated by using the finite difference time domain （FDTD） method.In addition,for the wavelength of 1.55 m,a kind of application structure with the lattice constant a=405 nm and the radius of air holes R=135 nm which can restrict the transmission of beams in photonic crystal without defect is proposed and simulated.The structure which can collimate the output beam and compress its divergence angle is easy to design.It has wide application prospects in optical communication and three-dimensional （3D） imaging lidar systems.

Compact Terahertz Wave Collimator Design with Photonic Crystal Slabs

A compact terahertz （THz） wave collimator is proposed, which works under the frequency from 2.4 THz to 2.7 THz with a photonic crystal （PC） slab based on the self-collimation effect. The plane wave expansion （PWE） method is used to calculate the dispersion surfaces and the equal-frequency contours （EFCs） and optimize the structure. The propagation of the THz waves in the structure is simulated and the normalized transmission is calculated by using the finite-difference time-domain （FDTD） method with perfectly matched layer （PML） absorbing boundary conditions. Numerical simulations show that the designed collimator has a good collimation property and a high transmittance.

NEW METHOD OF REDUCING HEAT DEFORMATION OF SLIDEWAY GRINDERS

A new concept used for designing large-scale and high-precision NC slideway grinders which are called self-collimation slideway grinders is introduced to eliminate thermal deformation of them. Its principle is to make use of gravitational deformation of machine beds and their foundations automatically to compensate for thermal deformation caused by environmental temperature fluctuation and friction heat between machine tables and machine beds by decreasing longitudinal section stiffness of machine beds and foundations. By FEM analysis and application of more than 10 years, it shows that they have advantages of high precision and low cost, moreover, no constant temperature rooms are required. The linearity error of parts machined with them is less than 0.003 mm/m, and machining precision can almost keep constant for a long time.

Brillouin Klein space and half-turn space in three-dimensional acoustic crystals

The Bloch band theory and Brillouin zone(BZ)that characterize wave-like behaviors in periodic mediums are two cornerstones of contemporary physics,ranging from condensed matter to topological physics.Recent theoretical breakthrough revealed that,under the projective symmetry algebra enforced by artificial gauge fields,the usual two-dimensional(2D)BZ(orientable Brillouin two-torus)can be fundamentally modified to a non-orientable Brillouin Klein bottle with radically distinct manifold topology.However,the physical consequence of artificial gauge fields on the more general three-dimensional(3D)BZ(orientable Brillouin three-torus)was so far missing.Here,we theoretically discovered and experimentally observed that the fundamental domain and topology of the usual 3D BZ can be reduced to a non-orientable Brillouin Klein space or an orientable Brillouin half-turn space in a 3D acoustic crystal with artificial gauge fields.We experimentally identify peculiar 3D momentum-space non-symmorphic screw rotation and glide reflection symmetries in the measured band structures.Moreover,we experimentally demonstrate a novel stacked weak Klein bottle insulator featuring a nonzero Z2 topological invariant and self-collimated topological surface states at two opposite surfaces related by a nonlocal twist,radically distinct from all previous 3D topological insulators.Our discovery not only fundamentally modifies the fundamental domain and topology of 3D BZ,but also opens the door towards a wealth of previously overlooked momentum-space multidimensional manifold topologies and novel gaugesymmetry-enriched topological physics and robust acoustic wave manipulations beyond the existing paradigms.