In this presentation, I will present the findings of a compact depth sensing system for LiDAR that is based on a metasurface. I will explain the underlying design concept of this metasurface, which utilizes structured light to expand the range of view angles for point cloud generation. Two separate cameras, capture the generated point cloud, and depth information is calculated using the stereo-matching method. Additionally, I will propose electrically adjustable metalens that can be easily incorporated into AR/VR systems and electronic systems. These metaphotonic devices offer potential applications in diverse fields such as mobile sensors, biometric security systems, autonomous driving, metaverse, and driver assistance.
In this presentation, I will introduce the result of a metasurface-based compact depth sensing system that can be applied to LiDAR. I will explain the design principle of this structured light metasurface which can spread the point cloud with a large field of view angles. This spread point cloud is captured by two distinct cameras, and depth information is computed by the stereo-matching method. And I will suggest electrically tunable metalens which can be easily integrated with not only AR/VR systems but also electronic systems. These metaphotonic devices have the potential to be applied to various fields such as mobile sensors, biometric security systems, autonomous driving, metaverse, and driver assistance.
Plasmonic resonance energy transfer (PRET) based imaging has been proposed as an effective label-free real-time biomolecular absorption spectroscopic method that enables the detection of biomolecules and dynamic cell activities. Here, we present a metasurface-based PRET-imaging platform that effectively engineers the darkfield scattering spectrum using the gap plasmon and grating effect. As a demonstration, three different biomolecules (Cyt c, Chl a, Chl b) are simultaneously detected using our metasurface-based PRET-imaging platform. Our proposed metasurface-based PRET-imaging platform enables continuous monitoring in the spatial region and multiplexed PRET sensing of multiple biomolecules with different absorption spectrums in the visible.
Optical resolution photoacoustic microscopy (OR-PAM) provides high optical contrast and lateral resolution. However, the resolution of a typical OR-PAM using an objective lens is limited to not exceeding Abbe's optical diffraction limit. In this study, a lensless shear force scanning PAM is presented. Instead of a lens, the system uses an imaging probe that combines a non-coated tapered fiber with a quartz tuning fork (QTF). A shear force feedback mechanism is used to maintain a tens of nm (near-field) distance between the fiber tip and the sample. With the system, PA signals generated in the near field of a gold sputtered glass sample were successfully acquired. We also performed 2D PA scanning experiments and obtained PA images of gold cube samples with high lateral resolution. This study demonstrates the existence of a near field PA signal and shows its potential for super-resolution scanning PAM.
The chiroptical effects are omnipresent throughout the universe and play a vital role in the sorting and detecting enantiomers in numerous applications like life sciences, pharmaceuticals, agrochemicals, food industry, etc. These chiroptical effects, along with polarization retention and full phase modulation, can have a significant potential for applications such as chiral imaging, anti-counterfeiting, and security. For strong chiroptical effects, all-dielectric metadevices offer a compact and efficient substitute to three-dimensional (3D) chiral metamaterials and flat plasmonic metadevices, which are prone to complex fabrication and ohmic losses, respectively. Here, we propose a unique metasurface based on the combination of achiral structures to achieve chiroptical effect with polarization retention and wavefront shaping. The proposed structure reflects the left hand circularly polarized (LHCP) light while preserving its handedness with complete absorption of the right hand circularly polarized (RHCP) and vice versa. Meanwhile, the structure provides full 2π phase modulation designed by hydrogenated amorphous silicon (a-Si:H), which is a low-loss, CMOS (complementary metal-oxide-semiconductor) compatible material with fabrication ease. The spin-selective reflection with circular dichroism and full phase modulation of designed structure find application in integrated optics, quantum optics, detection, and chiral imaging.
In this abstract, I will discuss our efforts in realizing ultra-sharp nanoantennas with radius of curvature of 1 nm and 5 nm nanogap for extreme photon squeezing applications. Firstly, we propose an unconventional nanolithography technique called cascade domino lithography (CDL) to realize such sharp tip structures. By controlling collapse of micro/nanopillar photoresist structures, diverse plasmonic nanogap structures or single-digit nanometer scale structures can be realized, which are not obtainable with conventional nanofabrications. Secondly, we analyze the optical characteristics of sharp bowtie nanoantennas by using numerical simulations and near/far-field experiments. For instances, an extreme field localization and enhancement are verified by finite-difference time-domain (FDTD) simulations along with near-field scanning optical microscopy (NSOM) measurement, nonlinear spectroscopy and surface-enhanced Raman spectroscopy (SERS).
Metasurface, 2D counterpart of metamaterials, has been of great interests due to its capability of manipulating light’ properties such as amplitude, phase, polarization, and angular momentum. Individual property of light is quite freely modulated using metasurface; modulation of the several properties in single metasurface has been intensively explored. This multifunctional metasurfacs has a high potential to increase optical information channels of the optical data storage device. In this study, we propose duplex metasurface which contains structurally colored print and vectorial holograms with eight polarization channels. The encoded structural color prints can be observed under white light and the fully polarized holograms can be reconstructed using coherent laser source with combination of output polarizer/retarder. As a proof-of-concept, we devise optical security platform using our multifunction metasurface and propose detection device using liquid crystal (LC) cell.
In this abstract, I will discuss our efforts in realizing multifunctional metaholograms that can encode multiple pieces of information in a monolayer device for anticounterfeiting applications. First, I will present a spin-multiplexed visible metahologram [1]. A straightforward method for encoding multiple pieces of information in a single metahologram device is using polarization. To obtain significant birefringence for the control and reversal of photon spin, two sets of nanorods are designed, and depending on their orientation, they imprint inversed spin photons along their corresponding geometrical phase. As a result, this allows switching between two different images by simply flipping the handedness of the circularly polarized light on the transmission-type metahologram with 61% diffraction efficiency. Second, I will introduce a direction-multiplexed visible metahologram [2]. This approach is to multiplex two distinct pieces of information onto a monolayer metahologram operating in the forward and backward directions depending on the direction of light incident on the device. Particularly, in this part we will reveal underlying physics of high transmission efficiency (around 75%), which is the antiferromagnetic resonances in the a-Si:H nanorod. Finally, I will propose a wavelength-multiplexed visible/NIR switchable metahologram. The device consists of a-Si:H and gold (Au) metasurfaces in a monolayer device, which is fabricated by the electron beam lithography overlay process [3]. The a-Si:H metasurfaces generate a visible hologram and the Au metasurfaces produce a invisible(NIR) hologram simultaneously with low crosstalk. I believe our efforts for making a multiplexed metahologram will lead to pragmatic anticounterfeiting applications.
In this abstract, I will discuss our efforts in realizing active thin film color filters and stimuli-responsive dynamic metaholograms for advanced display applications. Firstly, as a proof of concept for carrier concentration-controlled tunable device, we propose a tunable all solid-state color filter based on indium gallium zinc oxide (IGZO) active layer in a metal/dielectric/IGZO/metal cavity structure. By modulating the carrier concentration of IGZO, a resonance peak from the structure can be shifted around 50 nm in visible. Secondly, the stimuli-responsive metaholograms with designer liquid crystal will be discussed. To realize electrically tunable or other external stimuli (heat and surface pressure)-reactive metahologram, we adopt the functionalized liquid crystal in the spin-encoded metahologram. This kind of approach will may open up new emerging applications such as hologram mark for food safety (such as beverage freshness over temperature) and tangible holographic displays.
Recently emerged metasurfaces, the two-dimensional (2D) counterpart of three dimensional (3D) metamaterials, gained significant attention in optics and photonics due to their less challenging fabrication requirements (compared to 3D metamaterials) and unique capabilities of wavefront manipulation by introducing abrupt phase shift. Realization of multiple functionalities in a single metasurface, is an intriguing perception to achieve further miniaturization and cost effectiveness. In this paper, we propose a polarization insensitive, highly efficient metasurfaces for the visible spectrum. For the design wavelength of 633nm, negligible absorption coefficient (k) and adequately large refractive index (n) of proposed hydrogenated amorphous silicon (a-Si:H) leads to considerably efficient and cost-effective solution towards metasurfaces design. Inherent property of cylindrical pillar to be polarization insensitive is exploited and 400 nm thick cylindrical nano–waveguide is opted as building block to construct the metasurface. A novel design strategy of achieving multiple functionalities from a single metasurface is proposed, where a combined effect of lensing and optical vortices with different topological charges at different focal planes is demonstrated for the proof of concept. Such unique design strategy of integrating multiple phases into a single device provides an innovative way of miniaturizing the optical devices and systems exhibiting versatile functionalities for on–chip applications.
Miniaturized devices with multiple functionalities are exceedingly required in integrated optical systems. Flat nanostructures, named metasurfaces, provide fascinating boulevard for complex structuring and manipulation of light such as optical vortex generation, lensing, imaging, harmonic generation etc. at micron scale. Since, the performance of metal-based plasmonic metasurfaces is significantly limited by their optical absorption and losses, lossless dielectric materials (in the operational spectrum) provide decent alternative to attain higher efficiency. Here, a novel, polarization insensitive and highly efficient method for light structuring is demonstrated based on amorphous silicon (with subwavelength thickness of 400 nm) at an operational wavelength of 633 nm. The proposed phase gradient metasurface is based on circular cylindrical nanopillars of amorphous silicon exhibits two optical properties, the lensing and orbital angular momentum generation. The cylindrical nature of the pillar plays a pivotal role to make the overall structure as polarization insensitive. The proposed innovative methodology will provide an interesting road towards the development and realization of multi-functional ultrathin nanodevices which will find numerous applications in integrated photonics.
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