Keywords dielectric metasurface, multifoci metalens, optical vortex multiplexing, spatial multiplexing metasurface, twofold polarization-selective metasurface

Optical metasurface has exhibited unprecedented capabilities in the regulation of light properties at a subwavelength scale. In particular, a multifunctional polarization metasurface making use of light polarization to integrate distinct functionalities on a single platform can be greatly helpful in the miniaturization of photonic systems and has become a hot research topic in recent years. Here, we propose and demonstrate an efficient all-dielectric diatomic metasurface, the unit cell of which is composed of a pair of a-Si:H-based nanodisks and nanopillars that play the roles as polarization-maintaining and polarizationconverting meta-atoms, respectively. Through rigorous theoretical analyses and numerical simulations, we show that a properly designed diatomic metasurface can work as a nanoscale linear polarizer for generating linearly polarized light with a controllable polarization angle and superior performances including a maximum transmission efficiency of 96.2% and an extinction ratio of 32.8 dB at an operation wavelength of 690 nm. Three metasurface samples are fabricated and experimentally characterized to verify our claims and their potential applications. Furthermore, unlike previously reported dielectric diatomic metasurfaces which merely manipulate the polarization state, the proposed diatomic metasurface can be easily modified to empower 1-bit phase modulation without altering the polarization angle and sacrificing the transmission efficiency. This salient feature further leads to the demonstration of a metasurface beam splitter that can be equivalently seen as the integration of a nonpolarizing beam splitter and a linear polarizer, which has never been reported before. We envision that various metadevices equipping with distinct wavefront shaping functionalities can be realized by further optimizing the diatomic metasurface to achieve an entire 2π phase control.

We propose and demonstrate an optical phased-array-based bidirectional grating antenna (BDGA) in silicon nitride waveguides. The BDGA is integrated with a miniaturized all-dielectric metasurface doublet (MD) formed on a glass substrate. The BDGA device, which takes advantage of alternately feeding light to its ports in opposite directions, is presumed to effectively provide a doubled wavelength-tuned steering efficiency compared to its unidirectional counterpart. The MD, which is based on vertically cascaded convex and concave metalenses comprising circular hydrogenated amorphous silicon nanopillars, is meticulously placed atop the BDGA chip to accept and deflect a beam emanating from the emission area, thereby boosting the beam-steering performance. The manufactured BDGA could achieve an enhanced beam-steering efficiency of 0.148 deg/nm as well as a stable spectral emission response in the wavelength range of 1530–1600 nm. By deploying a fabricated MD atop the silicon photonic BDGA chip, the steering efficiency was confirmed to be boosted by a factor of ∼ 3.1 , reaching 0.461 deg/nm, as intended.

A light-driven diffraction grating incorporating two grating patterns with different pitches atop a photothermal actuator (PTA) has been proposed. It is based on graphene oxide/reduced graphene oxide (GO/rGO) induced via femtosecond laser direct writing (FsLDW). The rGO, its controllable linewidth, and transmission support the formation of grating patterns; its noticeably small coefficient of thermal expansion (CTE), good flexibility, and thermal conductivity enable the fabrication of a PTA consisting of a polydimethylsiloxane layer with a relatively large CTE. Under different intensities of light stimuli, diffraction patterns can be efficiently tailored according to different gratings, which are selectively addressed by incident light beam hinging on the bending of the PTA. This is the first demonstration of combining gratings and PTA, wherein the GO plays the role of a bridge. The light-driven mechanism enables the contactless operation of the proposed device, which can be efficiently induced via FsLDW. The diffraction angle could be changed between 2° and 6° horizontally, and the deviation of side lobes from the main lobe could be altered vertically in a continuous range. The proposed device may provide powerful support for activating dynamic diffraction devices in photothermally contactless schemes.

“Lab‐on‐fiber” technology, which combines the unique merits of optical fibers with nanophotonic platforms, has received significant investigation due to its profound ability to control light at the nanoscale, which has significantly boosted the functionalities of conventional fibers. Previous plasmonic‐based fiber meta‐tips (FMTs) have been inhibited by the intrinsic ohmic losses of the metallic structures, resulting in limited light manipulation efficiency. In addition, to become prominent candidates for integrated photonics, their functional diversity needs to be enhanced. In this study, an FMT constructed by tethering an all‐dielectric metasurface to a single‐mode fiber for bifunctional light manipulation is implemented. Distinct light manipulation, including vortex generation and beam collimation, is executed by tailoring the phase profiles encoded in the metasurface for transverse electric and transverse magnetic polarized light. To build the proposed FMT, a polarization‐selective metasurface is first created via lithography nanofabrication and then attached to an optical fiber with the aid of a vision system. Moreover, as a proof‐of‐concept, the feasibility of exploiting the established FMT for applications such as optical interconnects is demonstrated. The resulting fiber optics and metasurface‐based meta‐tip represent a major breakthrough in the lab‐on‐fiber technology roadmap for applications such as optical communication, optical trapping, and biological sensing.