Low-loss metasurface optics down to the deep ultraviolet region

Shrinking conventional optical systems to chip-scale dimensions will benefit custom applications in imaging,displaying,sensing,spectroscopy,and metrology.Towards this goal,metasurfaces-planar arrays of subwavelength electromagnetic structures that collectively mimic the functionality of thicker conventional optical elements-have been exploited at frequencies ranging from the microwave range up to the visible range.Here,we demonstrate highperformance metasurface optical components that operate at ultraviolet wavelengths,including wavelengths down to the record-short deep ultraviolet range,and perform representative wavefront shaping functions,namely,highnumerical-aperture lensing,accelerating beam generation,and hologram projection.The constituent nanostructured elements of the metasurfaces are formed of hafnium oxide-a loss-less,high-refractive-index dielectric material deposited using low-temperature atomic layer deposition and patterned using high-aspect-ratio Damascene lithography.This study opens the way towards low-form factor,multifunctional ultraviolet nanophotonic platforms based on flat optical components,enabling diverse applications including lithography,imaging,spectroscopy,and quantum information processing.

Multifunctional metasurfaces enabled by simultaneous and independent control of phase and amplitude for orthogonal polarization states

Monochromatic light can be characterized by its three fun dame ntal properties:amplitude,phase,and polarization.In this work,we propose a versatile,transmission-mode all-dielectric metasurface platform that can independently manipulate the phase and amplitude for two orthogonal states of polarization in the visible frequency range.For proof-o仁concept experimental demonstration,various single-layer metasurfaces composed of subwavelength-spaced titanium-dioxide nanopillars are designed,fabricated,and characterized to exhibit the ability of polarization-switchable multidimensional light-field manipulation,including polarization-switchable grayscale nanoprinting,nonuniform cylindrical lensing,and complex-amplitude holography.We envision the metasurface platform dem on strated here to open new possibilities toward creating compact multifunctional optical devices for applications in polarization optics,information encoding,optical data storage,and security.

Photonic waveguide to free-space Gaussian beam extreme mode converter

Integration of photonic chips with millimeter-scale atomic,micromechanical,chemical,and biological systems can advance science and enable new miniaturized hybrid devices and technology.Optical interaction via small evanescent volumes restricts performance in applications such as gas spectroscopy,and a general ability to photonically access optical fields in large free-space volumes is desired.However,conventional inverse tapers and grating couplers do not directly scale to create wide,high-quality collimated beams for low-loss diffraction-free propagation over many millimeters in free space,necessitating additional bulky collimating optics and expensive alignment.Here,we develop an extreme mode converter,which is a compact planar photonic structure that efficiently couples a 300 nm×250 nm silicon nitride high-index single-mode waveguide to a well-collimated near surface-normal Gaussian beam with an≈160μm waist,which corresponds to an increase in the modal area by a factor of>105.The beam quality is thoroughly characterized,and propagation over 4mm in free space and coupling back into a single-mode photonic waveguide with low loss via a separate identical mode converter is demonstrated.To achieve low phase error over a beam area that is>100×larger than that of a typical grating coupler,our approach separates the two-dimensional mode expansion into two sequential separately optimized stages,which create a fully expanded and well-collimated Gaussian slab mode before out-coupling it into free space.Developed at 780 nm for integration with chip-scale atomic vapor cell cavities,our design can be adapted for visible,telecommunication,or other wavelengths.The technique can be expanded to more arbitrary phase and intensity control of both large-diameter,free-space optical beams and wide photonic slab modes.

Subnanometer localization accuracy in widefield optical microscopy

The common assumption that precision is the limit of accuracy in localization microscopy and the typical absence of comprehensive calibration of optical microscopes lead to a widespread issue—overconfidence in measurement results with nanoscale statistical uncertainties that can be invalid due to microscale systematic errors.In this article,we report a comprehensive solution to this underappreciated problem.We develop arrays of subresolution apertures into the first reference materials that enable localization errors approaching the atomic scale across a submillimeter field.We present novel methods for calibrating our microscope system using aperture arrays and develop aberration corrections that reach the precision limit of our reference materials.We correct and register localization data from multiple colors and test different sources of light emission with equal accuracy,indicating the general applicability of our reference materials and calibration methods.In a first application of our new measurement capability,we introduce the concept of critical-dimension localization microscopy,facilitating tests of nanofabrication processes and quality control of aperture arrays.In a second application,we apply these stable reference materials to answer open questions about the apparent instability of fluorescent nanoparticles that commonly serve as fiducial markers.Our study establishes a foundation for subnanometer localization accuracy in widefield optical microscopy.

Towards integrated photonic interposers for processing octave-spanning microresonator frequency combs

Microcombs-optical frequency combs generated in microresonators-have advanced tremendously in the past decade,and are advantageous for applications in frequency metrology,navigation,spectroscopy,telecommunications,and microwave photonics.Crucially,microcombs promise fully integrated miniaturized optical systems with unprecedented reductions in cost,size,weight,and power.However,the use of bulk free-space and fiber-optic comp on ents to process microcombs has restricted form factors to the table-top.Taking microcomb-based optical frequency synthesis around 1550 nm as our target application,here,we address this challenge by proposing an integrated photonics interposer architecture to replace discrete components by collecting,routing,and interfacing octave-wide microcomb-based optical signals between photonic chiplets and heterogeneously integrated devices.Experimentally,we con firm the requisite performa nee of the individual passive elements of the proposed interposer一octave-wide dichroics,multimode interferometers,and tunable ring filters,and implement the octave-spanning spectral filteri ng of a microcomb,central to the in terposer,using silicon n itride phot onics.Moreover,we show that the thick silicon nitride needed for bright dissipative Kerr soliton generation can be integrated with the comparatively thin silicon nitride interposer layer through octave-bandwidth adiabatic evanescent coupling,indicating a path towards future system-level consolidation.Fin ally,we numerically confirm the feasibility of operating the proposed in terposer synthesizer as a fully assembled system.Our interposer architecture addresses the immediate need for on-chip microcomb processing to successfully miniaturize microcomb systems and can be readily adapted to other metrology-grade applications based on optical atomic clocks and high-precision navigation and spectroscopy.

Transfer of motion through a microelectromechanical linkage at nanometer and microradian scales

Mechanical linkages are fundamentally important for the transfer of motion through assemblies of parts to perform work.Whereas their behavior in macroscale systems is well understood,there are open questions regarding the performance and reliability of linkages with moving parts in contact within microscale systems.Measurement challenges impede experimental studies to answer such questions.In this study,we develop a novel combination of optical microscopy methods that enable the first quantitative measurements at nanometer and microradian scales of the transfer of motion through a microelectromechanical linkage.We track surface features and fluorescent nanoparticles as optical indicators of the motion of the underlying parts of the microsystem.Empirical models allow precise characterization of the electrothermal actuation of the linkage.The transfer of motion between translating and rotating links can be nearly ideal,depending on the operating conditions.The coupling and decoupling of the links agree with an ideal kinematic model to within approximately 5%,and the rotational output is perfectly repeatable to within approximately 20 microradians.However,stiction can result in nonideal kinematics,and input noise on the scale of a few millivolts produces an asymmetric interaction of electrical noise and mechanical play that results in the nondeterministic transfer of motion.Our study establishes a new approach towards testing the performance and reliability of the transfer of motion through assemblies of microscale parts,opening the door to future studies of complex microsystems.

Optimized sintering and mechanical properties of Y-TZP ceramics for dental restorations by adding lithium disilicate glass ceramics

The novel dental ceramics can be fabricated at lower temperatures when sol-gel derived lithium disilicate glass ceramics(LDGC)was used as an additive for yttria stabilized tetragonal zirconia polycrystalline(Y-TZP)ceramics.The effect of LDGC on the sintering,mechanical,and translucent properties of Y-TZP ceramics was investigated in the present study.The results showed that the LDGC additive effectively improved the densification of Y-TZP at 1100℃,which was much lower than the sintering temperature for pure Y-TZP.When sintered at 1100℃,the Y-TZP with 1 wt%LDGC reached a relative density of 95.45%,and prossessed a flexural strength of 482.4 MPa and a fracture toughness of 5.94 MPa-m12.Moreover,its translucency was also improved.While,the addition of LDGC could result in an escape of yttrium atoms from the grain lattice of zirconia,which induced the tetragonal-monoclinic transformation of zirconia and abnormal growth of monoclinic grains.The escaped yttrium atoms diffused into the intergranular glass phase.The results indicated that the novel Y-TZP-LDGC ceramics has a great potential to be used for all-ceramic restorations.

Transition metal on topological chiral semimetal PdGa with tailored hydrogen adsorption and reduction

The difficulties in designing high-performance hydrogen evolution reaction(HER)catalysts lie in the manipulation of adsorption behaviors of transition metals(TMs).Topological chiral semimetals with super-long Fermi arc surface states provide an ideal platform for engineering the catalytic performance of TMs through the metal-support interaction.We found the adsorption trends of TMs can be modified significantly when deposited at the surface of the PdGa chiral crystal.The electron transfer from the TMs to the surface states of the PdGa reshapes the d band structure of TMs and weakens the hydrogen intermediate bonding.Especially,W/PdGa is expected to be a good HER catalyst with close to zero Gibbs free energy.Experimentally,we found a Pt-like exchange current density and tumover frequency when depositing W atoms at the PdGa nanostructures surface.The findings provide a way to develop high-efficient electrocatalysts by the interplay between topological surface states and metal-support interaction.