An official website of the United States government
Multiple reflections from electrically large hemispherical lens surfaces of lens-integrated antennas are investigated using an iterative Huygens’ integral approach. In particular for mmW- and THz-band applications, double-slot antennas on extended hemispherical high-resistivity Silicon lenses have been widely used due to the high Gaussisicity of their radiation/ reception patterns. Previous studies assumed an electrically-large lens and evaluated the antenna pattern using first-order physical optics approximation. Although this approach is fairly accurate for estimating the radiation pattern of such antennas, the reception pattern and the associated performance of receiving sensors need a more careful consideration due to the relatively large level of internal reflections from the concave boundary of the high index lens. Here, we present an iterative method to compute and study the effects of multiple reflections inside electrically large lenses. The rich nature of quasi-optical wave behavior is demonstrated through several examples corresponding to individual bounces of the incident, reflected, and transmitted waves from a double slot antenna.
more »
« less
Conformal Electrochemical Nanoimprinting of Silicon: Toward Bio‐Inspired Hierarchical Infrared Meta‐Optics
Abstract Nanostructured anti‐reflection metasurfaces for infrared lenses are designed for imaging in harsh environments such as dust (e.g., moon or battlefield), micrometeorites (e.g., Lagrange points), and high‐radiation fluctuations (e.g., Mars) with limited lifetimes. These multifunctional optical meta‐surfaces (MOMS) simultaneously deliver high thermal stability and anti‐fouling behavior due to their monolithic nature (e.g., no mismatch in the coefficient of thermal expansion), hydrophobicity, and low dust adherence. However, the incompatibility of inorganic semiconductor micromachining with non‐planar substrates has limited MOMS to polymeric and glass lenses. Here, a new method of conformal electrochemical nanoimprinting is presented to directly micromachine a nature‐inspired MOMS onto a silicon lens. Uniquely, stretchablegold‐coated patterned porous PVDF stamps are made by lithographically templated thermally induced phase separation (lt‐TIPS), which simultaneously embeds it with (i) interconnected porosity for promoting mass transport, (ii) HF‐resistance for increasing operational lifetime, and (iii) stretchable electronic nanocoatings (i.e., Au) that can catalyze the electrochemical process. In a demonstration of its hierarchical micromachining capability, a sharklet microscale pattern is successfully transferred to a silicon lens with anti‐reflective and hydrophobic properties. This work paves the way for MOMS’ extension onto inorganic semiconductors and IR lenses.
more »
« less
- PAR ID:
- 10633201
- Publisher / Repository:
- Advanced Materials
- Date Published:
- Journal Name:
- Advanced Materials
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Metal‐assisted electrochemical nanoimprinting (Mac‐Imprint) scales the fabrication of micro‐ and nanoscale 3D freeform geometries in silicon and holds the promise to enable novel chip‐scale optics operating at the near‐infrared spectrum. However, Mac‐Imprint of silicon concomitantly generates mesoscale roughness (e.g., protrusion size ≈45 nm) creating prohibitive levels of light scattering. This arises from the requirement to coat stamps with nanoporous gold catalyst that, while sustaining etchant diffusion, imprints its pores (e.g., average diameter ≈42 nm) onto silicon. In this work, roughness is reduced to sub‐10 nm levels, which is in par with plasma etching, by decreasing pore size of the catalyst via dealloying in far‐from equilibrium conditions. At this level, single‐digit nanometric details such as grain‐boundary grooves of the catalyst are imprinted and attributed to the resolution limit of Mac‐Imprint, which is argued to be twice the Debye length (i.e., 1.7 nm)—a finding that broadly applies to metal‐assisted chemical etching. Last, Mac‐Imprint is employed to produce single‐mode rib‐waveguides on pre‐patterned silicon‐on‐insulator wafers with root‐mean‐square line‐edge roughness less than 10 nm while providing depth uniformity (i.e., 42.9 ± 5.5 nm), and limited levels of silicon defect formation (e.g., Raman peak shift < 0.1 cm−1) and sidewall scattering.more » « less
-
We demonstrate focusing as well as imaging using diffractive microoptics, manufactured by two-photon polymerization grayscale lithography (2GL), that have been 3D printed into porous silicon oxide. While typical doublet lens systems require support structures that hold the lenses in place, our optics are held by the porous media itself, decreasing both the fabrication time and design constraints while increasing the optically active area. Compared to the typical two-photon polymerization fabrication process, 2GL offers better shape accuracy while simultaneously increasing throughput. To showcase 2GL manufactured optics in porous media, we fabricate singlet diffractive lenses with a diameter of 500 µm and numerical apertures of up to 0.6. We measure the intensity distribution in the focal plane, and along the optical axis. Furthermore, we design and fabricate a doublet lens system for imaging purposes with a diameter of 600 µm and thinner than 60 µm. We examine the imaging performance with a USAF 1951 resolution test chart and determine the resolution to be 287 lp/mm. 3D printing in porous SiO2thus holds great promise for future complex and unconventional microoptical solutions.more » « less
-
We previously demonstrated how the Sn3Ag4Ti alloy can robustly bond onto silicon via selective laser melting (SLM). By employing this technology, thermal management devices (e.g., micro-channels, vapor chamber evaporators, heat pipes) can be directly printed onto the electronic package (silicon die) without using thermal interface materials. Under immersion two-phase cooling (pool boiling), we compare the performance of three chip cooling methods (conventional heat sink, bare silicon die and additively manufactured metal micro-fins) under high heat flux conditions (100 W/cm2 ). Heat transfer simulations show a significant reduction in the chip temperature for the silicon micro-fins. Reduction of the chip operating temperature or increase in clock speed are some of the advantages of this technology, which results from the elimination of thermal interface materials in the electronic package. Performance and reliability aspects of this technology are discussed through experiments and computational models.more » « less
-
We experimentally demonstrate imaging in the long-wave infrared (LWIR) spectral band (8 μm to 12 μm) using a single polymer flat lens based upon multilevel diffractive optics. The device thickness is only 10 μm, and chromatic aberrations are corrected over the entire LWIR band with one surface. Due to the drastic reduction in device thickness, we are able to utilize polymers with absorption in the LWIR, allowing for inexpensive manufacturing via imprint lithography. The weight of our lens is less than 100 times those of comparable refractive lenses. We fabricated and characterized 2 different flat lenses. Even with about 25% absorption losses, experiments show that our flat polymer lenses obtain good imaging with field of view of 35° and angular resolution less than 0.013°. The flat lenses were characterized with 2 different commercial LWIR image sensors. Finally, we show that, by using lossless, higher-refractive-index materials like silicon, focusing efficiencies in excess of 70% can be achieved over the entire LWIR band. Our results firmly establish the potential for lightweight, ultrathin, broadband lenses for high-quality imaging in the LWIR band.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/adma.202504983
