Laser-based 3-D nanoprinting exemplified by two photon polymerization (TPP) has emerged as a practical route for additive manufacturing of sub-wavelength scale structures with broad applications in photonic packaging, nanofluidics, nanoelectromechanical systems, drug delivery, tissue engineering, and beyond. Conventional TPP relies on compound refractive lenses for light focusing. Here we present a novel alternative approach leveraging optical metalenses as the light manipulation element for versatile TPP fabrication. Using an inverse design algorithm, we show that the point spread function (PSF) of the metalens can be custom tailored to realize a variety of TPP writing modes, enabling fabrication of unconventional geometries difficult to process with traditional TPP. We demonstrated integration of metalenses with both commercial and home-built TPP systems, and experimentally implemented TPP to writing of 3-D polymer microstructures.
With their recognized advantages such as system-level size, weight and power (SWaP) benefits, minimal monochromatic aberration, polarization discrimination capacity, and low-cost at scale, metasurfaces have emerged as a transformative optics technology. Optical distortion, an important metric in many optical design specifications, has however rarely been discussed in the context of metalens optics. Here we present we present a generic approach for on-demand distortion correction using wide field-of-view (FOV) compound metalenses.
The mid-infrared (mid-IR) spectral region contains the characteristic vibrational absorption bands of most molecules as well as two atmospheric transmission windows, and is therefore of critical importance to many biomedical, military, and industrial applications such as spectroscopic sensing, thermal imaging, free-space communications, and infrared countermeasures. Metasurface devices operating in the mid-IR potentially offer significantly reduced size, weight, and cost compared to traditional bulk optics, but they are also challenged with unique material and processing requirements. By combining high-index, broadband transparent dielectric materials with a Huygens metasurface design, we have experimentally realized high-performance metasurface devices with a low-profile, deep sub-wavelength thickness. Based on the platform, we demonstrated single-layer metalenses with focusing efficiencies up to 75% and diffraction-limited performance over a record field of view close to 180 degrees. These meta-optical devices can provide significantly enhanced design flexibility for future infrared optical systems.
The mid-wave infrared (MWIR) is an important band for numerous applications ranging from night vision to biochemical sensing. However, unlike visible or near-infrared (NIR) optical parts, which are economically available off the shelf, MWIR optics are plagued by much higher costs and often inferior performance compared to their visible or NIR counterparts. Optical metasurfaces, artificial materials with subwavelength-scale thicknesses and on-demand electromagnetic responses, provide a promising solution for cost-effective, high-performance infrared optics. Using high-refractive-index (> 5) chalcogenide materials deposited on IR-transparent substrates, we have experimentally demonstrated a MWIR transmissive metasurface device with diffraction-limited focusing and imaging performance and optical efficiency up to 75%. We further show that the metasurface design can accommodate ultra-wide field-of-view and the fabrication method can be extended to conformal integration of metasurface optics on curved surfaces. The projected size, weight and power advantages, coupled with the manufacturing scalability leveraging standard microfabrication technologies, makes the meta-optical devices promising for next-generation MWIR system applications.
Optical phase change materials (O-PCMs) are a unique class of materials which exhibit extraordinarily large optical property change (e.g. refractive index change > 1) when undergoing a solid-state phase transition. These materials, exemplified by Mott insulators such as VO2 and chalcogenide compounds, have been exploited for a plethora of emerging applications including optical switching, photonic memories, reconfigurable metasurfaces, and non-volatile display. These traditional phase change materials, however, generally suffer from large optical losses even in their dielectric states, which fundamentally limits the performance of optical devices based on traditional O-PCMs. In this talk, we will discuss our progress in developing O-PCMs with unprecedented broadband low optical loss and their applications in novel photonic systems, such as high-contrast switches and routers towards a reconfigurable optical chip.
Two-dimensional (2-D) materials are of tremendous interest to silicon photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. Here we present a new route for 2-D material integration with silicon photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides achieving improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators based on graphene and black phosphorus.
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