We have recently studied the physics and functionalities of metasurfaces in both reflective and transmissive geometries, with passive and actively tunable functionalities. In the first part, we first present a complete phase diagram to understand/predict the diversified and fascinating functionalities of metasurfaces in metal-insulator-metal (MIM) configuration , based on which we combined graphene with metasurface to achieve wide-range active THz phase modulation . We next describe our recent efforts to realize tunable metasurfaces in the microwave regime to realize dynamically-controllable functionalities . In the second part, we will describe our recent efforts to realize surface-plasmon-polariton (SPP) meta-couplers with very high efficiencies, based on gradient metasurfaces . Finally, we show that 100%-efficiency photonic spin-Hall effect (PSHE) can be realized in geometric-phase metasurfaces with meta-atoms satisfying certain criterions, which help us design microwave metasurfaces exhibiting nearly 100% PSHE efficiency in both reflection and transmission geometries .
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Photonic spin hall effect (PSHE), that spin-polarized photons can be laterally separated in transportation, gains increasing attention from both science and technology, but available mechanisms either require bulky systems or exhibit very low efficiencies. Here we demonstrate that a giant PSHE with ~100% efficiency can be realized at certain meta-surfaces with deep-subwavelength thicknesses. Based on rigorous Jones-Matrix analysis, we establish a general criterion to design meta-surfaces that can realize 100%-efficiency PSHE. The criterion is approachable from two distinct routes at general frequencies. As a demonstration, two microwave meta-surfaces are fabricated and then experimentally characterized, both showing ~90% efficiencies for the PSHE. Our findings pave the road for many exciting applications based on high-efficiency manipulations of photon spins, with a polarization detector experimentally demonstrated here as an example.
Surface plasmon polaritons (SPPs) have found numerous applications in photonics, but traditional devices to excite them (such as grating and prism couplers) all suffer inherent low-efficiency issues, since the generated SPPs can decouple back to free space and the reflection at the device surface can never be avoided. Here, based on a transparent gradient metasurface, we propose a new SPP-excitation scheme and numerically demonstrate that it exhibits inherently high efficiency ( 94%), since the designed meta-coupler kills both the decoupling and the reflection at its surface. As a proof of concept, we fabricate a meta-coupler in the microwave regime, and combine near- and far-field experiments to demonstrate that the achieved SPP-excitation efficiency reaches 75%, which is several times higher than all other available devices. Our findings can inspire the designs and realizations of high-performance plasmonic devices to harvest light-matter interactions.
Holograms, the optical devices to reconstruct pre-designed images, have been evolved dramatically since the advances in today’s nanotechnology [1-4]. Metamaterials, the sub-wavelength artificial structures with tailored refraction index, enable us to design the meta-hologram working in arbitrary frequency region. Here we demonstrated the first reflective type, dual image and high efficient meta-hologram with the incident angle as well as the coherence of incident wave insensitivity in visible region at least from λ = 632.8 nm to λ = 850 nm. The meta-hologram is composed of 50-nm-thick gold cross nano-antenna coupled with 130-nm-thick gold mirror with a 50-nm-thick MgF<sub>2</sub> as spacer. It shows different images “RCAS” and “NTU” with high image contract under x- and y-polarized illumination, respectively. Making use of the characteristic of meta-materials, these optical properties of proposed meta-hologram can be transferred to arbitrary electromagnetic region by scale-up the size of the unit cell of meta-hologram, leading to more compact, efficient and promising electromagnetic components.