Joon-Suh Park

Harvard University | Harvard · Area of Applied Physics

Metasurfaces, with their ability to control electromagnetic waves, hold immense potential in optical device design, especially for applications requiring precise control over dispersion. This work introduces an approach to dispersion engineering using heterogeneous freeform metasurfaces, which overcomes the limitations of conventional metasurfaces...

Mult-layered meta-optics have enabled complex wavefront shaping beyond their single layer counterpart owing to the additional design variables afforded by each plane. For instance, complex amplitude modulation, generalized polarization transformations, and wide field of view are key attributes that fundamentally require multi-plane wavefront matchi...

When light scatters off an object, its polarization, in general, changes—a transformation described by the object’s Mueller matrix. Mueller matrix imaging is an important technique in science and technology to image the spatially varying polarization response of an object of interest, to reveal rich information otherwise invisible to traditional im...

Metasurfaces, optics made from subwavelength-scale nanostructures, have been limited to millimeter-sizes by the scaling challenge of producing vast numbers of precisely engineered elements over a large area. In this study, we demonstrate an all-glass 100 mm diameter metasurface lens (metalens) comprising 18.7 billion nanostructures that operates in...

A set of nanostructures capable of creating high-efficiency, broadband metasurfaces for visible wavelengths is presented. Utilizing structure-induced dispersion engineering, we show that anisotropic-shaped nanostructures are effective building blocks for crafting broadband, polarization-insensitive, and efficient metasurfaces.[1]

Metasurfaces, optics made from subwavelength-scale nanostructures, have been limited to millimeter-sizes by the scaling challenge of producing vast numbers of precisely engineered elements over a large area. In this study, we demonstrate an all-glass 100 mm diameter metasurface lens (metalens) comprising 18.7 billion nanostructures that operates in...

Phase singularities are loci of darkness surrounded by monochromatic light in a scalar field, with applications in optical trapping, super-resolution imaging, and structured light-matter interactions. Although 1D singular structures, like optical vortices, are common due to their robust topological properties, uncommon 0D (point) and 2D (sheet) sin...

When light scatters off an object its polarization, in general, changes - a transformation described by the object's Mueller matrix. Mueller matrix imaging polarimetry is an important technique in science and technology to image the spatially varying polarization response of an object of interest, to reveal rich information otherwise invisible to t...

Dispersion results from the variation of index of refraction as well as electric field confinement in sub-wavelength structures. It usually results in efficiency decrease in metasurface components leading to troublesome scattering into unwanted directions. In this letter, by dispersion engineering, we report a set of eight nanostructures whose disp...

Metasurfaces are a new class of diffractive optical elements with subwavelength elements whose behavior can be lithographically tailored. By leveraging form birefringence, metasurfaces can serve as multifunctional freespace polarization optics. Metasurface gratings are novel, to the best of our knowledge, polarimetric components that integrate mult...

We simulated a free-standing metasurface-based Faraday rotator design. The device gives a high transmittance, large Faraday rotation angle, and figure of merit ~24 times higher than a conventional device at the wavelength of 755nm.

Mueller matrix imaging, an important technique in STEM, images the information-rich spatially varying polarization properties of an object. Using nanoengi-neered metasurfaces, we implement a compact Mueller imaging system that can, in a single-shot, acquire images for all sixteen Mueller matrix components.

We present a path to truly ‘flat’, all-oxide metalenses working at visible wavelength comprising high-aspect ratio TiO 2 nanopillars infused into fused silica substrate. We show both a proof-of-concept infused metalens using electron-beam lithography, and an example of mass-manufacturing using deep-ultraviolet projection lithography.

We demonstrate a high efficient metalens designed to operate at VUV (175 nm) wavelengths. This wavelength is typically found in scintillation light detection used in high energy physics experiments.

Phase singularities are loci of darkness surrounded by monochromatic light in a scalar field, with applications in optical trapping, super-resolution imaging, and structured light-matter interactions. Although 1D singular structures, such as optical vortices, are the most common due to their robust topological properties, uncommon 0D (point) and 2D...

In this Letter, we investigate a new class of polarization wave front transformations which exhibit nonconventional far field interference behavior. We show that these can be realized by double-layer metasurfaces, which overcome the intrinsic limitations of single-layer metasurfaces. Holograms that encode four or more distinct patterns in nonorthog...

Metasurfaces have been extensively engineered to produce a wide range of optical phenomena, allowing exceptional control over the propagation of light. However, they are generally designed as single-purpose devices without a modifiable postfabrication optical response, which can be a limitation to real-world applications. In this work, we report a...

Access to the complete spatiotemporal response of matter due to structured light requires field sampling techniques with sub-wavelength resolution in time and space. We demonstrate spatially resolved electro-optic sampling of near-infrared waveforms, providing a versatile platform for the direct measurement of electric field dynamics produced by ph...

Metasurfaces have been extensively engineered to produce a wide range of optical phenomena, allowing unprecedented control over the propagation of light. However, they are generally designed as single-purpose devices without a modifiable post-fabrication optical response, which can be a limitation to real-world applications. In this work, we report...

Meta-optics has achieved major breakthroughs in the past decade; however, conventional forward design faces challenges as functionality complexity and device size scale up. Inverse design aims at optimizing meta-optics design but has been currently limited by expensive brute-force numerical solvers to small devices, which are also difficult to real...

An array of ten identical, blue-detuned atom traps with 3D confinement generated by inverse-designed metasurface is presented, a proof-of-concept for metasurfaces as a compact and versatile means for multi-atom optical traps in quantum optics.

We present a mass-producible, all-glass, 100 mm diameter metalens working at visible wavelengths manufactured using deep-ultraviolet projection lithography, overcoming the intrinsic exposure size limit of the lithography tool.

Metasurfaces are arrays of sub-wavelength spaced nanostructures, which can be designed to control the many degrees-of-freedom of light on an unprecedented scale. In this work, we design meta-gratings where the diffraction orders can perform general, arbitrarily specified, polarization transformation without any reliance on conventional polarization...

Optical phase singularities are zeros of a scalar light field. The most systematically studied class of singular fields is vortices: beams with helical wavefronts and a linear (1D) singularity along the optical axis. Beyond these common and stable 1D topologies, we show that a broader family of zero-dimensional (point) and two-dimensional (sheet) s...

Meta-optics has achieved major breakthroughs in the past decade; however, conventional forward design faces challenges as functionality complexity and device size scale up. Inverse design aims at optimizing meta-optics design but has been currently limited by expensive brute-force numerical solvers to small devices, which are also difficult to real...

Virtual and augmented realities are rapidly developing technologies, but their large-scale penetration will require lightweight optical components with small aberrations. We demonstrate millimeter-scale diameter, high-NA, submicron-thin, metasurface-based lenses that achieve diffraction-limited achromatic focusing of the primary colors by exploitin...

Beyond one-dimensional optical singularity topologies, we demonstrate zero-dimensional (point) and two-dimensional (sheet) singularities. We engineer phase and polarization sheet singularities through inverse-design, by maximizing the field phase gradient, and demonstrate metasurface-enabled realizations of each.

Metalenses are optical devices that implement nanostructures as phase shifters to focus incident light. Their compactness and simple fabrication make them a potential cost-effective solution for increasing light collection efficiency in particle detectors with limited photosensitive area coverage. Here we report on the characterization and performa...

Significance Nanostructured metamaterials have been engineered to generate a wide range of optical phenomena, allowing an unprecedented control over the propagation of light. However, they are generally designed as single-purpose devices without a modifiable optical response, which can be a barrier to applications. In this work, we report the nontr...

In this talk, we will present a new platform for a virtual/augmented reality system based on a metalens and a fiber scanning display. The metalens was designed for achromatic focusing of blue, green, and red light. The fiber scanning display features combined desired merits of high resolution, high brightness, high dynamic range and wide color gamu...

Metalenses are optical devices that implement nanostructures as phase shifters to focus incident light. Their compactness and simple fabrication make them a potential cost-effective solution for increasing light collection efficiency in particle detectors with limited photosensitive area coverage. Here we report on the characterization and performa...

We demonstrated a large and RGB-achromatic metalens by novel design methods. Furthermore, we realized a compact platform for a virtual reality / augmented reality system based on an RGB metalens and a fiber scanning display.

Metalenses, planar lenses realized by placing subwavelength nanostructures that locally imparts lens-like phase shifts to the incident light, are promising as a replacement for refractive optics for their ultra-thin, lightweight, and tailorable characteristics, especially for applications where payload is of significant importance. However, the req...

With ever‐growing technological demands in the imaging sensor industry for autonomous driving and augmented reality, developing sensors that can satisfy not only image resolution but also the response speed becomes more challenging. Herein, the focus is on developing a high‐speed photosensor capable of obtaining high‐resolution, high‐speed imaging...

We present mass-producible, large area, single-material metalens working in the visible wavelength, using conventional deep-ultraviolet (DUV) stepper lithography technique. Having a diameter of 1 cm, our present lens show polarization independent, near-diffraction limited focusing behavior.

Flexible perovskite solar cells (PSCs) have attracted considerable attention due to their excellent performance, low-cost, and great potential as an energy supplier for soft electronic devices. In particular, the design of charge transporting layers (CTLs) is crucial to the development of highly efficient and flexible PSCs. Herein, nanocrystalline...

The control of the optoelectronic properties of the interlayers of perovskite solar cells (PSCs) is crucial for achieving high photovoltaic performances. Of the solution-processable interlayer candidates, NiOx is considered one of the best inorganic hole-transporting layer (HTL) materials. However, the power conversion efficiencies (PCEs) of NiOx-b...

Surface smoothing of indium tin oxide (ITO) film by laser irradiation was demonstrated. The ITO surface was etched by choline radicals, which were activated by laser irradiation at a wavelength of 532 nm. The RMS surface roughness was improved from 5.6 to 4.6 nm after 10 min of laser irradiation. We also showed the changes in the surface morphology...

Interface engineering is considered the key to improving the device performance and stability of solar cells. In particular, TiO2 nanostructures, when used as electron transporting layers (ETLs) in metal halide perovskite solar cells (PSCs), led to excellent power conversion efficiencies (PCEs) of over 20%. They effectively transferred charge carri...

The surface of poly(methyl methacrylate) (PMMA) film was etched by laser irradiation under O2 and vacuum conditions. By activating the O2 molecules near the rough surface, oxygen radicals will preferably etch the protrusions on the PMMA surface. Three lasers of different wavelengths were used for comparison. Laser irradiation at a short wavelength...

SiO2 is a commonly used insulation layer for QCLs but has high absorption peak around 8 to 10 µm. Instead of SiO2, we used Y2O3 as an insulation layer for DC-QCL and successfully demonstrated lasing operation at the wavelength around 8.1 µm. We also showed 2D numerical analysis on the absorption coefficient of our DC-QCL structure with various para...

Poly(3-hexylthiophene) (P3HT) is a promising p-type polymer to optimize the architecture, charge transfer, and environmental stability in electronic devices. Therefore, it can be a suitable material for a hole transporting layer in lead halide perovskite solar cells (PSCs). However, the mismatch of band alignment with perovskites suppresses efficie...

The effect of crystal orientation of CH3NH3PbI3 on photovoltaic properties has rarely been studied due to the lack of method to fabricate perovskite films with well-controlled crystal orientation in specific direction. Here, we have controlled the orientation of CH3NH3PbI3 crystal by changing organic precursors (CH3NH3I and CH3NH3Cl) and successful...

Colloidal quantum dots (QDs) have been extensively studied for optoelectronic and biological applications due to their unique physical and optical properties. In particular, among the optoelectronics applications, the white light emitting diode (WLED) has great potential in the flat panel displays and solidstate lighting. Here, we demonstrate a nov...

Although various colloidal quantum dot (QD) coating and patterning techniques have been developed to meet the demands in opto-electronic applications over the past years, each of the previously demonstrated methods has one or more limitations and trade-offs in forming multi-color, high-resolution, or large-area patterns of QDs. In this study, we pr...

To realize high-performance flexible perovskite solar cells (PSCs), electron selective layers (ESL) that can be processed at low temperatures are required. Here, we develop UV-assisted solution process to prepare highly compact Nb-doped TiO2 (UV-Nb:TiO2) ESLs at low temperature (<50 °C). Highly crystalline TiO2 nanocrystals (NCs) stabilized with ol...

On page 7899, S. J. Kwon, H. Ko, and co-workers report a promising plasmonic platform, prepared by a randomized array of silver nanoparticles, which greatly boosts near-IR-to-visible (green and red) luminescence from underlying upconversion nanoparticles (pale green particles) and substantially enhances near-IR photosensitivity. The silver particle...

Flexible metal halide perovskite solar cells (PSCs) have been considered promising wearable energy power sources. Recently, various multi-functional charge-transporting layers, with high conductivity and air stability, have been rapidly developed in order to improve device performance. The practical use of flexible PSCs requires the retention of th...

On page 4464, M. J. Ko, H. J. Son, and co-workers develop a flexible perovskite solar cell by applying a novel low-temperature solution-processable polymer (PhNa-1T) as a hole-transport material. Compared with conventional PEDOT:PSS, PhNa-1T effectively improves solar cell efficiency and device stability due to the pH-neutral property of PhNa-1T an...

A promising platform is suggested for three-order enhanced upconversion luminescence from the upconversion nanoparticles by utilizing the disordered array of plasmonic metal nanoparticles and its applications to the highly sensitive NIR photodetector application.

We fabricated perovskite solar cells with enhanced device efficiency based on vertically oriented TiO2 nanostructures using a nanoporous template of block copolymers (BCPs). Dimension and shape controllability of the nanopores of the BCP template allowed for the construction of one-dimensional (1-D) TiO2 nanorods and two-dimensional (2-D) TiO2 nano...

For realizing flexible perovskite solar cells (PSCs), it is important to develop low-temperature processable interlayer materials with excellent charge transporting properties. Herein, a novel polymeric hole-transport material based on 1,4-bis(4-sulfonatobutoxy)benzene and thiophene moieties (PhNa-1T) and its application as a hole-transport layer (...

Graphene has extremely high mobility with unique linear band dispersions at the Fermi level, referred to as the Dirac cones, but the absence of the energy gap limits its application for switching devices. To open an energy gap, theoretical studies so far have introduced certain perturbations to graphene in the real or momentum space and checked whe...

The fabrication process for the blue GaN inorganic light emitting diode (ILED) on flexible polyimide (PI) substrate by laser lift off (LLO) method was demonstrated. The GaN epi-structure was grown on patterned sapphire wafer. GaN samples were temporary bonded with polyimide substrate by flexible silver epoxy. Separation of the whole GaN LED film fr...

Solar energy has been sought as one of the prominent candidates among the energy harvesting methods. The energy conversion efficiency of solar cell is limited by its ability of harvesting energy from limited range in solar energy spectrum. We approach this issue by using the down-conversion effect with conventional CdSe quantum dots (QDs), increasi...