People

Dr. Shangjr Gwo, Professor of the Department of Physics at National Tsing Hua University – Life is Made up of the Sum of Every Moments. [ 下載 PDF ]

Claire Lin

Optical Metamaterials/Metasurfaces and their Applications

Special Issue: Optical Metamaterials/Metasurfaces and their Applications [ 下載 PDF ]

Ta-Jen Yen

Metasurfaces and Nanophotonic Devices [ 下載 PDF ]

Yuan-Wei Chang, Ai-Yin Liu, Ping-Chen Shen, Ssu-Chin Tseng, Hui-Hsin Hsiao

Metamaterials (MMs) are artificial composite materials composed of periodic subwavelength micro and nanostructures designed to manipulate electromagnetic responses. In the past, threedimensional metamaterials suffered from significant fabrication challenges due to their complex structural designs and the intrinsic metallic losses of plasmonic components at optical frequencies. Metasurfaces, characterized by a reduced dimensionality of MMs, possess much feasibility in realization. They usually consist of flat optical resonator arrays with spatially varying geometry and subwavelength separation. Upon the interaction with light, the engineering spatially varying amplitude, phase, and polarization response provides new degrees of freedom to accomplish polarization control and wavefront shaping. Their outstanding optical properties have led to the development of versatile ultrathin optical devices such as meta-lenses, wave plates, polarimetry, nonlinear optical devices, meta-holograms, optical sensors, etc.

Limitations of Refractive Lens Technology and the Development of Metalenses [ 下載 PDF ]

Chao-Chien Hsu, Yen-Chun Chen, Che-Chin Chen, Wei-Lun Hsu, Chih-Ming Wang

Conventional optical lenses are widely used; however, a single lens element is generally insufficient to correct optical aberrations effectively. As a result, modern optical systems typically rely on multi-element lens assemblies, which inevitably lead to increased system volume and weight. Metalenses, based on subwavelength-scale metasurface structures, employ arrays of nanostructures to achieve precise phase modulation, offering advantages such as compactness, lightweight design, and ease of integration. Compared with traditional Fresnel lenses, metalenses provide pixelated yet quasi-continuous phase control, completely eliminating the shadow regions commonly found in Fresnel lenses and thereby enabling higher optical efficiency. Nevertheless, achieving high numerical aperture (NA), achromatic operation, and aberration correction simultaneously with a single metalens often requires extremely steep phase gradients. According to the Nyquist sampling theorem, high-NA designs demand tiny unit-cell sizes, particularly near the lens periphery. Moreover, to maintain high efficiency, each Fresnel zone must be sampled with at least four discrete phase levels. These requirements significantly increase fabrication complexity and lead to efficiency degradation, thus limiting practical and commercial applications. Hybrid optical systems that combine refractive lenses and metalenses provide a practical solution by leveraging the complementary strengths of both approaches. In such systems, the conventional refractive lens performs the primary focusing function, while a metasurface-based corrector (meta-corrector) is dedicated to aberration correction. This division of functionality substantially reduces the required phase gradient, simplifies fabrication, and improves overall efficiency. Future development will need to address fabrication cost challenges, with commercialization driven by complementary metal–oxide–semiconductor (CMOS)-compatible processes. Hybrid optical systems show great potential in applications such as smartphone cameras, medical instruments, and automotive optics, and are expected to become a mainstream approach for next-generation lightweight optical systems.

Microcavity-assisted Multi-resonant High-Q Metasurfaces for Wavefront Engineering [ 下載 PDF ]

Pin-Chieh Wu

This article presents a novel microcavity-assisted multi-resonant high-Q metasurface platform that integrates Fabry-Perot cavity with a gradient-thickness distributed Bragg reflector (DBR). By introducing a wavelength-dependent cavity thickness, the proposed meta-optics architecture enables the simultaneous generation of multiple high-Q resonances spanning the visible to nearinfrared spectral range within a single layered metasurface. Unlike conventional single-resonant or multiplexed metasurface designs, this approach supports 15 high-Q resonance modes without sacrificing optical efficiency. By incorporating plasmonic meta-atoms with geometric phase control into the metasurface, independent and continuous 2π phase modulation can be achieved at each resonance wavelength, together with flexible amplitude control. This capability allows precise multi-wavelength wavefront engineering within a single device. Both numerical simulations and experimental demonstrations confirm the robustness and scalability of this platform. Potential applications include multi-color vectorial holography, structural color generation, optical information encryption, and high-density photonic encoding. This work provides a forward-looking metasurface design strategy that significantly expands the degrees of freedom for multi-wavelength, high-efficiency optical field manipulation.

Ultraviolet Metasurfaces for Advanced Molecular Spectroscopy and Nanofabrication [ 下載 PDF ]

Shang-Jie Shen, Ming-Lun Tseng

Metasurfaces, composed of subwavelength nanostructures, have expanded into the deepultraviolet (DUV, 200－300 nm) regime, offering new opportunities in biomedical spectroscopy, materials analysis, lithography, and ultrafast lasers. However, conventional optics face challenges in DUV due to strong material absorption and high fabrication costs. This article reviews the potential of DUV metasurfaces in spectroscopy and nanomanufacturing, highlighting their advantages in molecular absorption and resonant Raman scattering. We present recent demonstrations of aluminum plasmonic and silicon polaritonic metasurfaces that enhance DUV Raman signals, as well as aluminum nitride metalenses for DUV imaging and picosecond laser microfabrication. These advances highlight the potential of metasurfaces to enable compact, sensitive, and integrable DUV photonic devices.

Asymmetric OAM Generation via Dielectric Janus Metasurfaces [ 下載 PDF ]

Yao-Wei Huang

Janus metasurfaces, capable of versatile light manipulation depending on the direction of incidence, have been investigated from the microwave to the mid-infrared spectrum. However, previous designs often relied on spatial multiplexing or vertical stacking, leading to complex fabrication processes. Metallic Janus metasurfaces, due to their inherent material properties, also suffer from significant Ohmic losses in the visible range. In this work, we experimentally demonstrate single-layer TiO₂-based Janus metasurfaces with arbitrary polarization control, exhibiting directionally asymmetric functionalities in both spin and orbital angular momentum (OAM). We introduce a novel Jones matrix formulation specifically adapted for Janus metasurfaces, enabling the efficient generation of two distinct, high-purity OAM states of vortex beams at a wavelength of 532 nm, depending on the direction of incidence. This advancement enables compact and flexible phase manipulation, supporting applications such as lasers and optical combiners, and broadening the potential of metasurface technologies across diverse optical platforms.

Fabrication of Optical Metamaterials Using Focused Ion Beam [ 下載 PDF ]

Jun-Yu Ou

Metamaterials have been developed over the past two decades, leading to enormous progress in optics and nanophotonics. Most recently, the metamaterial lenses, also known as metalenses, have led the way in applications for consumer electronics and smartphones. In this article, the nanofabrication processes for the manufacturing of metamaterials were reviewed and discussed. The author proposed using the focused ion beam lithography for the fabrication of photonic metamaterial and nanomechanical reconfigurable metamaterial.

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GaN p-FET Performance Enhancement by Polarization Induced 2DHG at GaN/ScAlN-based Heterostructure [ 下載 PDF ]

Mau-Phon Houng

GaN p-FETs play an important role in power electronics but are limited by challenges such as difficult p-type doping, high ohmic contact resistance, and poor heat dissipation. Although recent advances have narrowed the performance gap with n-FETs, GaN p-FETs still fall short of the requirements for GaN power ICs. To overcome the limitations of doping-based approaches, polarization-induced two-dimensional hole gas (2DHG) structures in AlGaN/GaN heterojunctions was explored to achieve E-mode operation and improved performance. However, their characteristics remain insufficient for CMOS IC, likely due to suboptimal polarization effects. Recent research therefore focuses on heterostructures with stronger polarization fields-such as GaN/AlN, GaN/InGaN, and GaN/ScAlN, Among these, the GaN/ScAlN attracted the most attention. However, polarization-induced technology still faces several challenges, including epitaxial growth techniques, interface engineering, device design and compatibility. Therefore, how to control and optimize the parameters to achieve the best performance of GaN p-FETs remains for further effort. After all, the realization of GaN CMOS power ICs depends on improving the characteristics of GaN p-FETs, and the GaN/ScAlN-based structure seems to the most promising one.

When “More Moore” Turns to “the Continued Rise of System Performance Density” [ 下載 PDF ]

Vincent Tung