The dielectric metasurface hologram promises higher efficiencies due to lower absorption than its plasmonic counterpart. However, it has only been used, up to now, for controlling linear-polarization photons to form single-plane holographic images in the near-infrared region. Here, we report a transmissiontype metahologram achieving images in three colors, free from high-order diffraction and twin-image issues, with 8-level modulation of geometric phase by controlling photon spin via precisely patterned Si nanostructures with varying orientations. The resulting real and virtual holographic images with spin dependence of incident photons natively enable the spin degeneracy removal of light, leading to a metahologram-enabled spin Hall effect of light. Low-absorption dielectrics also enable us to create holograms for short-wavelength light down to 480 nm, thus spanning the three primary colors. It possesses the potential for compact color-display chips using mature semiconductor processes, and holds significant advantages over previous metaholograms operating at longer wavelengths.

We report a kind of broadband electromagnetic boundary mode at an interface of anti-parallel magnetized media, which can only propagate in one direction perpendicular to the magnetization and parallel to the interface. The unidirectionality of this mode originates from the permeability or permittivity tensor introduced by magnetization. We theoretically and numerically analyze the existence of the unidirectional mode, and point out that this mode can exist in both gyromagnetic and gyroelectric medium. We also propose a one-way waveguide based on this unidirectional mode, which may realize a new kind of electromagnetic isolation differing from those existing ones.

We demonstrate the phenomenon of nonreciprocal extraordinary optical transmission (NEOT) through metallic film with slits on the substrate of magneto-optical materials. Under uniformly magnetization, the system can show nonreciprocal transmission at near-IR frequency range. With a properly designed structure, the nonreciprocity can be as high as 57.6%. Numerical evidence shows that the nonreciprocal performance is sensitive to the incidence angle, as well as to the thickness of the substrate.

The traditional transformation-based cloak seems like it can only hide objects by bending the incident electromagnetic waves around the hidden region. In this paper, we prove that invisible cloaks can be applied to realize the overlapped optics. No matter how many in-phase point sources are located in the hidden region, all of them can overlap each other (this can be considered as illusion effect), leading to the perfect optical interference effect. In addition, a singular parameter-independent cloak is also designed to obtain quasi-overlapped optics. Even more amazing of overlapped optics is that if N identical separated in-phase point sources covered with the illusion media, the total power outside the transformation region is N2I0 (not NI0) (I0 is the power of just one point source, and N is the number point sources), which seems violating the law of conservation of energy. A theoretical model based on interference effect is proposed to interpret the total power of these two kinds of overlapped optics effects. Our investigation may have wide applications in high power coherent laser beams, and multiple laser diodes, and so on.

Based on acousto-optic modulation and grating diffraction, a high-power-pulsed ~2 μm laser with a wide tunable wavelength is realized in double-clad Tm fibers. A maximum average output power of 35.6 W is obtained with the 6 m fiber, which also provides a maximum pulse energy and peak power of 1.58 mJ and 5.6 kW, respectively. For the 6 m fiber length, a >20 W average power can be achieved over a 100 nm wavelength tuning range. Shortening the fiber length to 2 m and 1 m can extend the wavelength tuning range further to shorter spectral regimes (1892 nm and 1881 nm). Short fiber length also narrows the Q-switched pulse duration to 90 ns. This kind of high-power, high-pulse-energy, widely tunable, and narrow-bandwidth ~2 μm fiber lasers can find wide applications in various regions.