All-dielectric metalens based on the transmission phase was designed, which can uniformly shape a beam with a uniform energy distribution. The problems and related fixes for maintaining beam homogeneity and broad divergence angle simultaneously at 940 nm are explained. In order to solve the problem of wavefront shaping, based on the iterative design principle of complex surfaces such as freeform surfaces, a design scheme to shape the incident wavefront into 80° divergence angle wavefront was proposed. An effective, polarization-independent silicon nanopillar element is built based on the effective dielectric theory, and instead of using the conventional step size selection method, the size of each nanopillar is determined by the phase diameter function, covering the phase tuning from 0 to 2π.
Large angle beam splitter grating is an important optical element but the current design methods are mostly based on the scalar diffraction theory based on Thin Element Approximation approximation, which is difficult to evaluate and calculate well when large angle beam splitting is involved. In this work, a method combining finite difference time domain method with adjoint optimization is proposed. Each iteration only needs two electromagnetic simulations to obtain the gradient distribution of the grating structure region. Using this method, a 1×5 beam splitting grating with a splitting angle of 10 degrees is designed. The final uniformity error is 3.7%, and the total diffraction efficiency is 86.6%. For the two-dimensional splitter , a 3×5 beam splitting grating with a diffraction full angle of 82.4×14 degrees is designed. Under the condition of large angle beam splitting, good uniformity error can still be maintained, and the final uniformity error reaches 23.1%.
The Hall-effect metasurface described in this paper uses a combination of Pancharatnam-Berry ( PB ) phase and geometric phase to achieve independent phase control of different spin states. According to the established vector diffraction rigorous coupled wave model, the genetic algorithm is used to optimize the phase distribution of two different shaping effects. Then, different shaping functions are integrated into one device through the arrangement of metasurface microstructure units. By manipulating the polarization chirality of the incident light, the focusing and wavefront shaping of different spin-state photons can be realized at the same time, and two coaxially distributed composite spots can be obtained to achieve the purpose of multi-dimensional shaping of far-field spin-state photons. By this method, the central beam with better flat-top effect and the annular spot with larger radius can be obtained. The designed diffraction efficiency is greater than 90% and the spot uniformity is less than 15%. The welded products have both the smooth surface of semiconductor laser welding and the high aspect ratio of fiber laser welding.
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