configurations are no longer sufficient, either in terms of realizing certain crucial functionalities or in performance improvement. Compared to 2D structures, 3D structures have one more dimension, which enables more diversity in structure/ device design and is crucial in realizing richer physical interactions, better performance, and advanced functionalities. For example, to obtain a negative permeability from split ring resonators (SRRs) to construct negative index metamaterial, a vertical configuration of SRRs is needed to couple with the magnetic field, while planar SRRs can only couple with the electric field to obtain a negative permittivity. [4] With respect to device performance, 3D gold helixes [5] have larger polarization contrast than 2D chiral structures, [6] and dynamic 3D microcontainers [7] can realize drug delivery in a much more controllable way than absorption on 2D structures. [8] Therefore, 3D micro/nanostructures are of significant importance in such scenarios, acting as an indispensable supplement to the present 2D micro/nanostructures. However, the fabrication of 3D micro/nanostructures is a formidable challenge with the state-of-the-art equipment, because the traditional planar process cannot be used directly due to its 2D projection nature.Much effort has been devoted in past decades, and significant progress has been demonstrated with 3D micro/nanofabrication, which can be divided into two types of strategies. The first one is brand new technologies/equipment development, including 3D laser direct writing (LDW) [9] and focused ion beam (FIB) [10] processing using two-photon polymerization and ion beam milling/deposition to construct 3D structures. Great scientific advantages have been demonstrated in the fields of mechanics, optics, and biology using these techniques. [11] However, due to their intrinsic point-by-point writing style, the efficiency of LDW and FIB is limited. Moreover, the materials that can be proceeded by the two techniques are usually photoresists (two-photon absorption) and metals (FIB-assisted deposition), and transferring to other materials can be quite challenging in most cases. [5,12] The other strategy is a combination or modification of the technologies in planar processes (including lithography, deposition, and etching) and is referred to as "planar technology" in this review. In this strategy, a variety of 3D fabrication methods have been developed, such as multilayer stacking, [13] oblique angle deposition, [14] and self-aligned Compared to their 2D counterparts, 3D micro/nanostructures show larger degrees of freedom and richer functionalities; thus, they have attracted increasing attention in the past decades. Moreover, extensive applications of 3D micro/nanostructures are demonstrated in the fields of mechanics, biomedicine, optics, etc., with great advantages. However, the mainstream micro/nanofabrication technologies are planar ones; therefore, they cannot be used directly for the construction of 3D micro/nanostructures, making 3D fabrication at the m...

Coherent photon-emitter interfaces offer a way to mediate efficient nonlinear photon-photon interactions, much needed for quantum information processing. Here we experimentally study the case of a two-level emitter, a quantum dot, coupled to a single optical mode in a nanophotonic waveguide. We carry out few-photon transport experiments and record the statistics of the light to reconstruct the scattering matrix elements of one-and two-photon components. This provides direct insight to the complex nonlinear photon interaction that contains rich many-body physics.

We demonstrate theoretically and experimentally a plasmonic metasurface operating as a broadband polarization converter with adequate efficiency which can transform linearly polarized light into its orthogonal polarization in the near-infrared region. The unit cell of the specifically designed metasurfaces is composed of an asymmetric split-ring resonator (SRR) within a square metallic hole. The adequate polarization conversion rate arises from the enhancement of the cross-polarized electric field and the decrease in the co-polarized electric field induced by the symmetry breaking of the SRR. Furthermore, a broad operating frequency range results from the overlap of multiple polarization rotation responses, which are generated in the combined symmetry-breaking SRRs and square metallic holes. This ultrathin single-layer metasurface avoids the complicated fabrication process of multilayered and tridimensional polarization converters and offers more intriguing possibilities to design high-performance plasmonic metasurfaces for polarization modulation.