Over the past decade, sub-wavelength diffractive optics has emerged as a promising field of research, offering attractive optical characteristics that allow for the manipulation of the amplitude and phase of incident light on flat surfaces. In particular, metalenses have shown strong potential to replace bulk refractive optical elements with ultra-thin planar platforms. In this study, we present a comparative analysis of wavefront aberration between sub-wavelength, nano-sized dielectric metalenses and commercial plano-convex (PCX) lenses at an infrared (IR) wavelength of 1,550 nm. We developed an off-axis interferometry system to observe the point-spread function (PSF) at the focal plane from phase-resolved interference patterns. The phase distribution across the wavefront was observed and calculated using Zernike polynomials. Additionally, we measured the focal spot size, modulation-transfer function (MTF), and Strehl ratio. Through this analysis, we found that the metalenses demonstrate diffraction-limited characteristics and are strongly competitive or even superior to the commercial PCX lenses in most metrics under the designed monochromatic wavelength.
Beam steering devices can be used for various applications such as light detection and ranging and free space optical communication. The conventional methods for the beam steering are based on the mechanical rotation of mirrors and cause bulk form-factor and limited operation speed. The metasurfaces are arrays of dielectric or metallic antennas that can tailor the optical properties such as amplitude and phase at the deep subwavelength range. Here, we present the all-dielectric metasurface that can modulate the reflection phase >270° with high reflectivity >60% as a function of the individually applied voltage in the near infrared regime.
Photonic crystal (PhC) phosphor is a paradigm-shifting structural platform that the authors’ group has developed. In this study, two major changes are introduced to the existing two-dimensional PhC phosphor: an increase in the refractive index contrast by replacing the PhC backbone material and the planarization of phosphor surface by the squeegee method. Compared with the reference phosphor, the upgraded PhC phosphor exhibits ~59 times enhanced absorption (simulated) and ~7 times enhanced phosphor emission (experimental). Although already impressive, the huge gap between theory and experiment indicates ample room for further improvement through, for example, the refinements in device fabrication.
Metasurfaces provide versatile platforms for arbitrary wavefront shaping with designer optical response such as amplitude, phase, and polarization at the deep subwavelength regime. Tunable metasurfaces can bring additional degree of freedom in terms of the time-dependent change of these responses, which can pave a way for novel applications such as wide-field-of-view holographic display and light detection and ranging (LiDAR). In this talk, we present the all-dielectric metasurface array that can modulate the phase of light above 270° in reflection with high reflectivity over 60% as a function of the individually applied voltage in the near infrared regime.
Miniaturization of optical spectrometers has recently drawn a lot of attention due to the increasing needs of portable characterization systems for scientific, industrial, and consumer applications. At the same time, smartphones have technically evolved to become an everyday, ubiquitous device that provides numerous useful applications to consumers. Combining optical spectrometer and smartphone could lead to an explosion of new applications, especially in healthcare, biometrics, and food inspections, and change our daily life, making it more convenient, independent, and hyper-personalized.
In this work, we have developed a smartphone spectrometer in the visible and near infrared (NIR) ranges by directly integrating a 2 dimensional periodic array of band-pass filters on top of the smartphone’s image sensor. Each band pass filter is a silicon resonator consisting of a pair of Si/SiO₂ distributed Bragg reflectors (DBR), where each resonator’s transmitting wavelength is set by adjusting the thickness of the center Si layer. The DBR contains alternating, vertically-stacked TiO2 and SiN films with variable thicknesses while the top and bottom of the DBR were made of Al and Cu or Al reflectors for the visible and NIR ranges, respectively. The fabrication process was completely CMOS-compatible.
Using this smartphone spectrometer, we have proposed the concept of artificial-intelligence-powered spectral barcode for material identification and successfully demonstrated its use in drug identification. The accuracy of correctly identifying the type of drugs was ~99%. In addition, the smartphone spectrometer has also proven to correctly distinguish beef into three different classes according to the freshness.
The commoditization of photonics would be possible only with the development of photonic integrated circuits and appropriate volume applications that require them. As such an application, a light detection and ranging(LiDAR) sensor has recently been in strong demand from various applications including autonomous driving. In terms of technology, as silicon photonics enters an industrial phase and begins to utilize the existing CMOS infrastructure, photonic integrated circuits are also expected to enter a virtuous cycle of volume and cost. This work outlines the current status of LiDAR research using the silicon photonics platform in Samsung. Based on the III/V-on-Si technology, Samsung's platform enables the development of chip-scale LiDAR that integrates all photonic devices such as wavelength-tunable laser, semiconductor optical amplifier, and custom optical phased array. With the LiDAR chip in the core, a palm-top LiDAR module prototype including control and signal processing circuits is also presented. Then, initial application-level attempts in autonomous driving are presented in the hope of pathfinding towards the LiDAR commoditization, and more broadly, commoditization of photonics.
We demonstrate subwavelength scale color pixels in a CMOS compatible platform based on anti-Hermitian metasurfaces. In stark contrast to conventional pixels, spectral filtering is achieved through structural color rather than transmissive filters leading to simultaneously high color purity and quantum efficiency. The subwavelength anti-Hermitian metasurface sensor is able to sort three colors over a 100 nm bandwidth in the visible regime, independently of the polarization of normally-incident light. Furthermore, the quantum yield approaches that of commercial silicon photodiodes, with a responsivity exceeding 0.25 A/W for each channel. Our demonstration opens a new door to subwavelength pixelated CMOS sensors and promises future high-performance optoelectronic systems.
For the first time, we present an active 2D metasurface array and its demonstrated versatile beam steering. The array is composed of individually-addressable, gate-controlled 10×10 pixels where each pixel modulates the phase of light in reflection. Each pixel is a gated plasmonic nanoresonator with an indium tin oxide (ITO) layer embedded in its middle. When proper gate biases are applied to the array, the refractive index of the ITO layer changes, generating a phase gradient necessary for dynamic beam steering. By generating a reconfigurable binary phase grating, we have successfully demonstrated full-area, 2D arbitrary beam steering.
We present an electrically tunable metasurface and demonstrate an ultrafast beam steering and distance-ranging. A unit cell of the proposed device consists of plasmonic antennas and an ITO film as an active, tunable layer. By individually applying electrical biases to the top and bottom of the unit cell, we achieve in the near-infrared range a phase change up to 360 degrees while keeping the amplitude constant. An adjustable gradient phase profile allows for all solid-state-electronic beam steering. Using the Time-of-Flight principle, we demonstrate for the first time metaphotonic-light detection and ranging (Meta-LiDAR).
We report the wavefront analysis in subwavelength dielectric metalenses. Experimentally, Shack-Hartmann wavefront sensor systems were employed to obtain lens aberrations and they were compared with theoretical calculations using Finite-difference Time-domain (FDTD) simulation. We were able to compute modal coefficients with Zernike functions implemented in Matlab. The measured and simulated wavefronts from metalenses were expressed as a sum of Zernike modes, typically 36 modes including the main 6 coefficients: defocus, vertical and obliques astigmatisms, vertical and horizontal comas, and spherical aberration. To assess the quality of the results, we reconstructed to wavefront data from the computed Zernike coefficients and compared to the originals as well. These results give us more confidence and accurate information about the effectiveness for practical use of metalenses.
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