In this paper, two kinds of bi-layered chiral metamaterials were proposed to enhance the asymmetric transmission effects for circular polarized electromagnetic waves which are only found in planar chiral metamaterials according to previous studies. It was found that the magnitude of the asymmetric transmission parameters mainly depends on the distances between the two metal layers. With appropriate distance, the asymmetric transmission parameter for circular polarized electromagnetic waves can increase to 0.6. Moreover, both proposed configurations show no asymmetric transmission for linear polarized electromagnetic waves which is widely studied in other bi-layered metamaterials.

The three-dimensional (3D) and two-dimensional (2D) chiral metamaterials (CMMs) have been proved to exhibit circular dichroism and circular conversion dichroism, respectively. The layer-by-layer chiral metamaterials, as a category of 3D CMMs, are expected to show the same properties as bulk 3D structures (e.g. helices). However, in this paper, we demonstrated that the layer-by-layer CMMs exhibit circular dichroism and circular conversion dichroism simultaneously by using both theoretical and experimental methods. This work showed that asymmetric transmissions of circular polarizations can also be observed in layer-by-layer CMMs. Moreover, we provided some necessary requirements for the existing of asymmetric transmissions in layer-by-layer CMMs.

We studied numerically the transmission properties of a kind of layer-by-layer nonchiral metamaterial. Simulation results show that under certain off-normal incidence, giant circular polarization conversion occurs for both the right and left circularly polarized waves with a roughly 1 GHz operation band. Meanwhile, the copolarization transmissions are almost suppressed to zero, leading to the high purity circular polarization transformation. This phenomenon of giant circular polarization conversion is assumed to suffer from the strong magnetic response, which is illustrated by the surface current distributions of the structure. Compared with chiral structures, this nonchiral structure is easier to design and fabricate and is expected to be used as a promising circular polarization transformer.

In the past 20 years, semiconductor lasers have been widely used in medical, industrial, and communication applications, providing a revolutionary and powerful platform for the fifth generation and advanced manufacturing. Semiconductor laser has the advantages of small size, lightweight, high reliability and easy modulation, becoming increasingly popular. However, due to the laser diode emission mechanism limitation, the beam quality is inferior and cannot be directly applied and required to be handled by beam shaping. However, the packaging of multiple beam shaping optical components is accompanied by risks due to misalignment. The misalignment error of the optical components has a great hidden danger to the laser performance. As semiconductor lasers' power gradually increases, lasers' thermal management technology is also increasingly strict. Therefore, this article first reviews the beam shaping technology of semiconductor laser diode array. Secondly, the analysis of the influence of the array semiconductor laser optical device's misalignment is reviewed, and a feasible solution is proposed. Finally, it summarizes the researches on thermal management in high-power semiconductor lasers. This article aims to give readers a comprehensive and broad understanding of semiconductor laser packaging's technical difficulties and to recognize each corresponding solution.