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Tunable mode converter is a key component of channel switching and routing for optical communication system by adopting mode-division multiplexing. Traditional mode converter hardly implements high-order mode conversion and dynamic tunability simultaneously. In this study, we design a tunable mode converter filled with liquid crystal, which can convert fundamental mode into multiple high-order modes (TE0, TE1, and TE2) with a good performance and low intrinsic loss. For this multiple-objective task, we propose an inverse design framework based on the adjoint method. To experimentally prove our design, a tunable mode converter filled with air or water and a mode demultiplexer are fabricated to implement dynamic routing. The experimental results agree well with the simulation and reveal the crosstalk only around −7 dB. With its performance and efficiency, our proposed design flow can be a powerful tool for multifunction device design.

Generating 2D diffraction orders with uniform or tailored intensity distribution is highly desired for various applications including depth perception, parallel laser fabrication and optical tweezer. However, previous strategies lack the abilities to tailor multiple parameters of output light in different diffraction orders simultaneously. While such ability plays an important role in achieving various different functionalities parallelly. Here, we demonstrate a method for encoding arbitrary phase profiles to different diffraction orders with controllable polarization states by applying double-phase method into elaborately designed metasurface. Sixteen independent holograms that generated by GS algorithm are successfully encoded into 4 × 4 uniformly distributed diffraction orders. Hence, the predefined holographic images can be observed at the Fourier plane. Meanwhile, the corresponding polarization states of different orders are manipulated according to their Fourier coefficients. For verifying the polarization state of each holographic image, we calculate the Stokes parameter of each order from measured intensity distributions in the experiment. The proposed method provides an effective way to tailor multiple properties of output diffraction orders. Meanwhile, it may promote the realization of achieving various functionalities parallelly such as spectral-polarization imaging or phase-polarization detection and enhance the capabilities of optical communication systems.

In a wide range of applications such as healthcare treatment, environmental monitoring, food processing and storage, and semiconductor chip manufacturing, relative humidity (RH) sensing is required. However, traditional fiber-optic humidity sensors face the challenges of miniaturization and indirectly obtaining humidity values. Here, we propose and demonstrate an optical barcode technique by cooperating with RH meta-tip, which can predict the humidity values directly. Such RH meta-tip is composed of fiber-optic sensor based on surface plasmon resonance (SPR) effect and graphene oxide film as humidity sensitizer. While SPR sensor is composed of multimode fiber (MMF) integrated with metallic metasurface. Dynamic time warping (DTW) algorithm is used to obtain the warp path distance (WPD) sequence between the measured reflection spectrum and the spectra of the precalibrated database. The distance sequence is transformed into a pseudo-color barcode, and the humidity value is corresponded to the lowest distance, which can be read by human eyes. The RH measurement depends on the collective changes of the reflection spectrum rather than tracking a single specific resonance peak/dip. This work can open up new doors to the development of a humidity sensor with direct RH recognition by human eyes.

As an inherent characteristic of light, polarization plays important roles in information storage, display and even encryption. Metasurfaces, composed of specifically designed subwavelength units in a two-dimensional plane, offer a great convenience for polarization manipulation, yet improving their integrability and broadband fidelity remain significant challenges. Here, based on the combination of various subwavelength cross-nanofins (CNs), a new type of metasurface for multichannel hybrid polarization distribution in near-field is proposed. Sub-wavelength CN units with various waveplate (WP) functionalities, such as frequency-division multiplexing WP, half-WP and quarter-WP are implemented with high efficiency in broadband. High-resolution grayscale image encryption, multi-image storage and rapid polarization detection are demonstrated by encoding the WP pixels into single, double and four channels, respectively. All these applications possess good fidelity in an ultrabroad wavelength band from 1.2 to 1.9 µm, and the high degree of integrability, easy fabrication and multifunction make the CN-shaped WP pixels a promising candidate in optical device miniaturization, quantum applications and imaging technologies.

Three-dimensional (3D) nanostructures have attracted widespread attention in physics, chemistry, engineering sciences, and biology devices due to excellent functionalities which planar nanostructures cannot achieve. However, the fabrication of 3D nanostructures is still challenging at present. Reliable fabrication, improved controllability, and multifunction integration are desired for further applications in commercial devices. In this review, a powerful fabrication method to realize 3D nanostructures is introduced and reviewed thoroughly, which is based on atomic layer deposition assisted 3D assembly through various sacrificial templates. The aim of this review is to provide a comprehensive overview of 3D nanofabrication based on atomic layer assembly (ALA) in multifarious sacrificial templates for 3D nanostructures and to present recent advancements, with the ultimate aim to further unlock more potential of this method for nanodevice applications.

The interactions of photonic spin angular momentum and orbital angular momentum, i.e., the spin-orbit coupling in focused beams, evanescent waves or artificial photonic structures, have attracted intensive investigations for the unusual fundamental phenomena in physics and potential applications in optical and quantum systems. It is of fundamental importance to enhance performance of spin-orbit coupling in optics. Here, we demonstrate a titanium dioxide (TiO2)–based all-dielectric metasurface exhibiting a high efficient control of photonic spin Hall effect (PSHE) in a transmissive configuration. This metasurface can achieve high-efficiency symmetric spin-dependent trajectory propagation due to the spin-dependent Pancharatnam-Berry phase. The as-formed metadevices with high-aspect-ratio TiO2 nanofins are able to realize (86%, measured at 514 nm) and broadband PSHEs in visible regime. Our results provide useful insights on high-efficiency metasurfaces with versatile functionalities in visible regime.

Metasurfaces are planar devices containing delicately designed nanoantenna or resonator arrays that allow for beam shaping, super resolution imaging, and holography. Hybrid metasurface – by integrating with tunable materials such as two-dimensional materials and phase change materials (PCMs) – provides a potential platform for active modulation of wavefronts. Specifically, PCMs can flexibly switch between crystalline and amorphous states with nonvolatile property under external stimuli and provide a large refractive permittivity contrast. Using metasurfaces based on PCM to manipulate wavefronts may provide new opportunities for switchable functionalities. Here, we propose two types of metasurface devices based on whole PCM films to realize switchable holography and simultaneous phase and interference encryption. This feature can be used to encrypt information in a switched state and store camouflage information in the other state by simply applying external thermal stimuli to the entire metasurface. This method can be applied in areas such as beam shaping, optical encryption, and anti-counterfeiting.

Metallic high aspect ratio (HAR) nano-architectures provide new opportunities for a series of plasmonic devices due to their additional controllable degrees in height space compared to 2D patterns, but there is no efficient way that suitable for the rapid fabrication of large area HAR structures limited by the processing ability of traditional methods. Here in this work, we have developed a templated electrochemical deposition (ECD) method to fabricate various HAR metallic nano-structures for diversified plasmonic devices. The templated ECD method is based on the ECD filling of the nanopores that are fabricated by electron beam lithography. With this templated ECD method, numbers of HAR architectures including nanorods, nanofins and even mushroom-like structures, which have a line width as small as 100 nm and the aspect ratio up to 10:1, are established over a large scale. What is more, by simultaneously considering the designed layout and edge effect, sub 10 nm nanogap arrays are prepared, whose aspect ratio reaches 100:1 and the gap width reduces to 5 nm. Due to the extreme light confinement ability brought from Fabry–Perot resonance, the HAR nanogaps can be treated as a surface enhanced Raman scattering (SERS) substrate. Finite domain time difference simulation shows that fan-like 10 nm nanogap with a height of 700 nm has the largest light enhancement factor (EF). The configuration optimized nanogap is capable for the sensing of rhodamine 6G with a 10−9 M concentration. And the SERS EF of the nanogap is calculated to be 4 × 106, indicating the ultrasensitive molecular detection ability of the HAR nanogap. The templated ECD method not only brings a new chance for the construction of HAR metallic 3D structures, but also opens up a new horizon for the design of a series of plasmonic devices.