We propose and present a high-efficiency circular dichroism device formed by an array of multi-size chiral slits etched in a silicon layer that is on a silicon dioxide substrate. Numerical results show that the all-dielectric chiral metasurface exhibits a high circular dichroism in the range of 1500-1550 nm. At the resonance wavelength of 1540 nm, the highest circular dichroism (CD = T<sub>RCP</sub>-T<sub>LCP</sub>) reaches 97%, and the extinction ratio (ER = T<sub>RCP</sub>/T<sub>LCP</sub>) is up to 1999:1. It is also found that multiple wavebands operation can be implemented by manipulating the relative positions of multi-size slits in the structure. The proposed 2D all-dielectric chiral metasurface has the advantages of high circular dichroism, easy-fabrication and high compatibility with linear polarized components, which provides a solution for pixelated full-Stokes polarization imaging.
Diverse passive harmonic mode-locking were observed in an all-normal-dispersion Yb-doped passively mode-locked fiber laser with a long cavity based on the nonlinear polarization rotation (NPR). Using a cascaded long-period fiber grating as a spectral filter, several modes of passively harmonic mode-locking including passive high-order harmonic mode-locking, passive multiple-pulse harmonic mode locking and passive large-pulse-width harmonic mode locking (over 300 ns ) were obtained by adjusting the tunable CW semiconductor laser (pumping source in the experiment) and polarization controller, in which the intense nonlinear effects, large fiber dispersion and phase bias played an important role. It is expected that the observed various modes of passive harmonic mode-locking may find applications in industrial fields where different pulse widths and repetition rates are needed and provide experimental evidence to the research of ultrafast lasers.
In this paper, a nano-polarization device based on two-photon polymerization reduction was designed and experimentally investigated. A broadband near-infrared (3-5 μ m) linear polarizer doped with metal particles was designed. Different from the fabrication methods of lithography and ion etching used in traditional metallic gratings or nanostructures, a two-photon absorption-based photo-reduction and photopolymerization process was adopted. The mixed solution composed by gold salt and photoresist is exposed by a femtosecend laser at a wavelength of 780 nm, at which the reduction reaction of the gold ions and the polymerization reaction of the resin are completed simultaneously, and thereby metal particles in the polymerized material can be obtained. The clusters of the reduced gold particles were observed by scanning electron microscopy, and the peak of gold was found in the energy dispersive X-ray spectrometer, which demonstrated the feasibility of the experiment and laid the foundation for the subsequent functional device fabrication.