%0 Journal Article %J SCIENCE ADVANCES %D 2018 %T Adaptive metalenses with simultaneous electrical control of focal length, astigmatism, and shift %A She, Alan %A Zhang, Shuyan %A Shian, Samuel %A David R. Clarke %A Federico Capasso %X Focal adjustment and zooming are universal features of cameras and advanced optical systems. Such tuning is usually performed longitudinally along the optical axis by mechanical or electrical control of focal length. However, the recent advent of ultrathin planar lenses based on metasurfaces (metalenses), which opens the door to future drastic miniaturization of mobile devices such as cell phones and wearable displays, mandates fundamentally different forms of tuning based on lateral motion rather than longitudinal motion. Theory shows that the strain field of a metalens substrate can be directly mapped into the outgoing optical wavefront to achieve large diffractionlimited focal length tuning and control of aberrations. We demonstrate electrically tunable large-area metalenses controlled by artificial muscles capable of simultaneously performing focal length tuning (> 100%) as well as onthe-fly astigmatism and image shift corrections, which until now were only possible in electron optics. The device thickness is only 30 mm. Our results demonstrate the possibility of future optical microscopes that fully operate electronically, as well as compact optical systems that use the principles of adaptive optics to correct many orders of aberrations simultaneously. %B SCIENCE ADVANCES %I AMER ASSOC ADVANCEMENT SCIENCE %C 1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA %V 4 %8 FEB %G eng %N 2 %9 Article %R 10.1126/sciadv.aap9957 %0 Journal Article %J NATURE NANOTECHNOLOGY %D 2018 %T A broadband achromatic metalens for focusing and imaging in the visible %A Wei Ting Chen %A Alexander Y. Zhu %A Vyshakh Sanjeev %A Mohammadreza Khorasaninejad %A Zhujun Shi %A Eric Lee %A Federico Capasso %X A key goal of metalens research is to achieve wavefront shaping of light using optical elements with thicknesses on the order of the wavelength. Such miniaturization is expected to lead to compact, nanoscale optical devices with applications in cameras, lighting, displays and wearable optics. However, retaining functionality while reducing device size has proven particularly challenging. For example, so far there has been no demonstration of broadband achromatic metalenses covering the entire visible spectrum. Here, we show that by judicious design of nanofins on a surface, it is possible to simultaneously control the phase, group delay and group delay dispersion of light, thereby achieving a transmissive achromatic metalens with large bandwidth. We demonstrate diffraction-limited achromatic focusing and achromatic imaging from 470 to 670 nm. Our metalens comprises only a single layer of nanostructures whose thickness is on the order of the wavelength, and does not involve spatial multiplexing or cascading. While this initial design (numerical aperture of 0.2) has an efficiency of about 20% at 500 nm, we discuss ways in which our approach may be further optimized to meet the demand of future applications. %B NATURE NANOTECHNOLOGY %I NATURE PUBLISHING GROUP %C MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND %V 13 %P 220+ %8 MAR %G eng %N 3 %9 Article %R 10.1038/s41565-017-0034-6 %0 Journal Article %J NANO LETTERS %D 2018 %T Broadband Achromatic Metasurface-Refractive Optics %A Wei Ting Chen %A Alexander Y. Zhu %A Jared Sisler %A Yao-Wei Huang %A Kerolos M.A. Yousef %A Eric Lee %A Cheng-Wei Qiu %A Federico Capasso %K achromatic metalens %K Dispersion engineering %K metasurface %K polarization-insensitive %K titanium dioxide %K Visible Spectrum %X Existing methods of correcting for chromatic aberrations in optical systems are limited to two approaches: varying the material dispersion in refractive lenses or incorporating grating dispersion via diffractive optical elements. Recently, single-layer broadband achromatic meta surface lenses have been demonstrated but are limited to diameters on the order of 100 mu cm due to the large required group delays. Here, we circumvent this limitation and design a metacorrector by combining a tunable phase and artificial dispersion to correct spherical and chromatic aberrations in a large spherical plano-convex lens. The tunability results from a variation in light confinement in sub-wavelength waveguides by locally tailoring the effective refractive index. The effectiveness of this approach is further validated by designing a metacorrector, which greatly increases the of a state-of-the-art immersion objective (composed of 14 lenses and 7 types of glasses) from violet to near-infrared wavelengths. This concept of hybrid metasurface-refractive optics combines the advantages of both technologies in terms of size, scalability, complexity, and functionality. %B NANO LETTERS %I AMER CHEMICAL SOC %C 1155 16TH ST, NW, WASHINGTON, DC 20036 USA %V 18 %P 7801-7808 %8 DEC %G eng %N 12 %9 Article %R 10.1021/acs.nanolett.8b03567 %0 Journal Article %J OPTICS EXPRESS %D 2018 %T Direct thermo-optical tuning of silicon microresonators for the mid-infrared %A L. Koehler %A P. Chevalier %A E. Shim %A B. Desiatov %A A. Shams-Ansari %A M. Piccardo %A Y. Okawachi %A Yu, M. %A Loncar, M. %A M. Lipson %A A. L. Gaeta %A F. Capasso %X We use light from a visible laser diode to directly tune silicon-on-chip microresonators by thermo-optical effect. We show that this direct tuning is local, non invasive and has a much smaller time constant than global temperature tuning methods. Such an approach could prove to be highly effective for Kerr comb generation in microresonators pumped by quantum cascade lasers, which cannot be easily tuned to achieve comb generation and soliton-modelocked states. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement %B OPTICS EXPRESS %I OPTICAL SOC AMER %C 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA %V 26 %P 34965-34976 %8 DEC 24 %G eng %N 26 %9 Article %R 10.1364/OE.26.034965 %0 Journal Article %J APL PHOTONICS %D 2018 %T Dynamic metasurface lens based on MEMS technology %A Tapashree Roy %A Zhang, Shuyan %A Il Woong Jung %A Troccoli, Mariano %A Federico Capasso %A Daniel Lopez %X In the recent years, metasurfaces, being flat and lightweight, have been designed to replace bulky optical components with various functions. We demonstrate a monolithic Micro-Electro-Mechanical System (MEMS) integrated with a metasurface-based flat lens that focuses light in the mid-infrared spectrum. A two-dimensional scanning MEMS platform controls the angle of the lens along two orthogonal axes by +/- 9 degrees, thus enabling dynamic beam steering. The device could be used to compensate for off-axis incident light and thus correct for aberrations such as coma. We show that for low angular displacements, the integrated lens-on-MEMS system does not affect the mechanical performance of the MEMS actuators and preserves the focused beam profile as well as the measured full width at half maximum. We envision a new class of flat optical devices with active control provided by the combination of metasurfaces and MEMS for a wide range of applications, such as miniaturized MEMS-based microscope systems, LIDAR scanners, and projection systems. (C) 2018 Author(s). %B APL PHOTONICS %I AMER INST PHYSICS %C 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA %V 3 %8 FEB %G eng %N 2 %9 Article %R 10.1063/1.5018865 %0 Journal Article %J EUROPEAN PHYSICAL JOURNAL PLUS %D 2018 %T Focus Point on Complex Photonics Measurements, Theory and Simulations for Extreme Light-Matter Interactions %A Pattelli, Lorenzo %A Wiersma, Diederik %A Brongersma, Mark %A Federico Capasso %B EUROPEAN PHYSICAL JOURNAL PLUS %I SPRINGER HEIDELBERG %C TIERGARTENSTRASSE 17, D-69121 HEIDELBERG, GERMANY %V 133 %8 MAR 19 %G eng %N 3 %9 Editorial Material %R 10.1140/epjp/i2018-11952-9 %0 Journal Article %J NANOPHOTONICS %D 2018 %T The future and promise of flat optics: a personal perspective %A Federico Capasso %K flat optics %K metalenses %K metasurfaces %K planar optics %K wavefront engineering. %X Metasurfaces enable the redesign of optical components into thin, planar and multifunctional elements, promising a major reduction in footprint and system complexity as well as the introduction of new optical functions. The planarity of flat optics will lead to the unification of semiconductor manufacturing and lens-making, where the planar technology to manufacture computer chips will be adapted to make CMOS-compatible metasurface-based optical components, ranging from metalenses to novel polarization optics, areas where I foresee the greatest technological and scientific impact. %B NANOPHOTONICS %I WALTER DE GRUYTER GMBH %C GENTHINER STRASSE 13, D-10785 BERLIN, GERMANY %V 7 %P 953-957 %8 JUN %G eng %N 6, SI %9 Review %R 10.1515/nanoph-2018-0004 %0 Journal Article %J LIGHT-SCIENCE & APPLICATIONS %D 2018 %T Giant intrinsic chiro-optical activity in planar dielectric nanostructures %A Alexander Y. Zhu %A Wei Ting Chen %A Aun Zaidi %A Yao-Wei Huang %A Mohammadreza Khorasaninejad %A Vyshakh Sanjeev %A Cheng-Wei Qiu %A Federico Capasso %K chiral %K dielectric %K extrinsic chirality %K metasurface %K optical activity %X The strong optical chirality arising from certain synthetic metamaterials has important and widespread applications in polarization optics, stereochemistry and spintronics. However, these intrinsically chiral metamaterials are restricted to a complicated three-dimensional (3D) geometry, which leads to significant fabrication challenges, particularly at visible wavelengths. Their planar two-dimensional (2D) counterparts are limited by symmetry considerations to operation at oblique angles (extrinsic chirality) and possess significantly weaker chiro-optical responses close to normal incidence. Here, we address the challenge of realizing strong intrinsic chirality from thin, planar dielectric nanostructures. Most notably, we experimentally achieve near-unity circular dichroism with similar to 90% of the light with the chosen helicity being transmitted at a wavelength of 540 nm. This is the highest value demonstrated to date for any geometry in the visible spectrum. We interpret this result within the charge-current multipole expansion framework and show that the excitation of higher-order multipoles is responsible for the giant circular dichroism. These experimental results enable the realization of high-performance miniaturized chiro-optical components in a scalable manner at optical frequencies. %B LIGHT-SCIENCE & APPLICATIONS %I CHINESE ACAD SCIENCES, CHANGCHUN INST OPTICS FINE MECHANICS AND PHYSICS %C 3888, DONGNANHU ROAD, CHANGCHUN, 130033, PEOPLES R CHINA %V 7 %8 FEB 23 %G eng %9 Article %R 10.1038/lsa.2017.158 %0 Journal Article %J ACS PHOTONICS %D 2018 %T Guided Modes of Anisotropic van der Waals Materials Investigated by near-Field Scanning Optical Microscopy %A Daniel Wintz %A Kundan Chaudhary %A Wang, Ke %A Jauregui, Luis A. %A Antonio Ambrosio %A Michele Tamagnone %A Alexander Y. Zhu %A Robert C. Devlin %A Crossno, Jesse D. %A Pistunova, Kateryna %A Kenji Watanabe %A Takashi Taniguchi %A Philip Kim %A Federico Capasso %K 2D materials %K hexagonal boron nitride %K near-field scanning optical microscopy %K optical constants %X Guided modes in nanometer thick anisotropic van der Waals materials are experimentally investigated and their refractive indices in visible wavelengths are extracted. Our method involves near-field scanning optical microscopy of waveguide (transverse electric) and surface plasmon polariton (transverse magnetic) modes in h-BN/SiO2/Si and Ag/h-BN stacks, respectively. We determine the dispersion of these modes and use this relationship to extract anisotropic refractive indices of h-BN flakes. In the wavelength interval 550-700 nm, the in-plane and out-of-plane refractive indices are in the range 1.98-2.12 and 1.45-2.12, respectively. Our approach of using near-field scanning optical microscopy allows for the direct study of the interaction between light and two-dimensional van der Waals materials and heterostructures. %B ACS PHOTONICS %I AMER CHEMICAL SOC %C 1155 16TH ST, NW, WASHINGTON, DC 20036 USA %V 5 %P 1196-1201 %8 APR %G eng %N 4 %9 Article %R 10.1021/acsphotonics.7b01518 %0 Journal Article %J OPTICS EXPRESS %D 2018 %T The harmonic state of quantum cascade lasers: origin, control, and prospective applications [Invited] %A Piccardo, Marco %A Chevalier, Paul %A Mansuripur, Tobias S. %A Kazakov, Dmitry %A Wang, Yongrui %A Noah A. Rubin %A Meadowcroft, Lauren %A Belyanin, Alexey %A Federico Capasso %X The recently discovered ability of the quantum cascade laser to produce a harmonic frequency comb has attracted new interest in these devices for both applications and fundamental laser physics. In this review we present an extensive experimental phenomenology of the harmonic state, including its appearance in mid-infrared and terahertz quantum cascade lasers, studies of its destabilization induced by delayed optical feedback, and the assessment of its frequency comb nature. A theoretical model explaining its origin as due to the mutual interaction of population gratings and population pulsations inside the laser cavity will he described. We explore different approaches to control the spacing of the harmonic state, such as optical injection seeding and variation of the device temperature. Prospective applications of the harmonic state include microwave and terahertz generation, picosecond pulse generation in the mid-infrared, and broadband spectroscopy. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement %B OPTICS EXPRESS %I OPTICAL SOC AMER %C 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA %V 26 %P 9464-9483 %8 APR 16 %G eng %N 8 %9 Article %R 10.1364/OE.26.009464 %0 Journal Article %J SCIENTIFIC REPORTS %D 2018 %T High-efficiency chiral meta-lens %A Benedikt Groever %A Noah A. Rubin %A J. P. BALTHASAR MUELLER %A Robert C. Devlin %A Federico Capasso %X We present here a compact metasurface lens element that enables simultaneous and spatially separated imaging of light of opposite circular polarization states. The design overcomes a limitation of previous chiral lenses reliant on the traditional geometric phase approach by allowing for independent focusing of both circular polarizations without a 50% efficiency trade-off. We demonstrate circular polarization-dependent imaging at visible wavelengths with polarization contrast greater than 20dB and efficiencies as high as 70%. %B SCIENTIFIC REPORTS %I NATURE PUBLISHING GROUP %C MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND %V 8 %8 MAY 8 %G eng %9 Article %R 10.1038/s41598-018-25675-3 %0 Journal Article %J OPTICS EXPRESS %D 2018 %T Inverse design of large-area metasurfaces %A Pestourie, Raphael %A Perez-Arancibia, Carlos %A Lin, Zin %A Shin, Wonseok %A Federico Capasso %A Steven G. Johnson %X We present a computational framework for efficient optimization-based ``inverse design'' of large-area ``metasurfaces'' (subwavelength-patterned surfaces) for applications such as multi-wavelength/multi-angle optimizations, and demultiplexers. To optimize surfaces that can be thousands of wavelengths in diameter, with thousands (or millions) of parameters, the key is a fast approximate solver for the scattered field. We employ a ``locally periodic'' approximation in which the scattering problem is approximated by a composition of periodic scattering problems from each unit cell of the surface, and validate it against brute-force Maxwell solutions. This is an extension of ideas in previous metasurface designs, but with greatly increased flexibility, e.g. to automatically balance tradeoffs between multiple frequencies or to optimize a photonic device given only partial information about the desired field. Our approach even extends beyond the metasurface regime to non-subwavelength structures where additional diffracted orders must be included (but the period is not large enough to apply scalar diffraction theory). (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement %B OPTICS EXPRESS %I OPTICAL SOC AMER %C 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA %V 26 %P 33732-33747 %8 DEC 24 %G eng %N 26 %9 Article %R 10.1364/OE.26.033732 %0 Journal Article %J SENSORS AND ACTUATORS B-CHEMICAL %D 2018 %T In-water fiber-optic evanescent wave sensing with quantum cascade lasers %A Chevalier, Paul %A Piccardo, Marco %A de Naurois, Guy-Mael %A Gabay, Ilan %A Katzir, Abraham %A Federico Capasso %K Attenuated total reflectance %K Fiber-optic evanescent wave spectroscopy %K Quantum cascade laser %K Silver-halide fiber %X The ability of detecting harmful chemicals is an important safety requirement for drinking water systems. An apparatus for in-water chemical sensing based on the absorption of evanescent waves generated by a quantum cascade laser array propagating in a silver halide optical fiber immersed into water is demonstrated. We present a theoretical analysis of the sensitivity of the system and experimentally characterize its real-time response and spectroscopic detection for injection of a sample chemical (ethanol) in a tube containing water. (C) 2018 Elsevier B.V. All rights reserved. %B SENSORS AND ACTUATORS B-CHEMICAL %I ELSEVIER SCIENCE SA %C PO BOX 564, 1001 LAUSANNE, SWITZERLAND %V 262 %P 195-199 %8 JUN 1 %G eng %9 Article %R 10.1016/j.snb.2018.01.159 %0 Journal Article %J OPTICS EXPRESS %D 2018 %T Large area metalenses: design, characterization, and mass manufacturing %A She, Alan %A Zhang, Shuyan %A Shian, Samuel %A David R. Clarke %A Federico Capasso %X Optical components, such as lenses, have traditionally been made in the bulk form by shaping glass or other transparent materials. Recent advances in metasurfaces provide a new basis for recasting optical components into thin, planar elements, having similar or better performance using arrays of subwavelength-spaced optical phase-shifters. The technology required to mass produce them dates back to the mid-1990s, when the feature sizes of semiconductor manufacturing became considerably denser than the wavelength of light, advancing in stride with Moore's law. This provides the possibility of unifying two industries: semiconductor manufacturing and lens-making, whereby the same technology used to make computer chips is used to make optical components, such as lenses, based on metasurfaces. Using a scalable metasurface layout compression algorithm that exponentially reduces design file sizes (by 3 orders of magnitude for a centimeter diameter lens) and stepper photolithography, we show the design and fabrication of metasurface lenses (metalenses) with extremely large areas, up to centimeters in diameter and beyond. Using a single two-centimeter diameter near-infrared metalens less than a micron thick fabricated in this way, we experimentally implement the ideal thin lens equation, while demonstrating high-quality imaging and diffraction-limited focusing. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement %B OPTICS EXPRESS %I OPTICAL SOC AMER %C 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA %V 26 %P 1573-1585 %8 JAN 22 %G eng %N 2 %9 Article %R 10.1364/OE.26.001573 %0 Journal Article %J APPLIED PHYSICS LETTERS %D 2018 %T Mid-infrared two-photon absorption in an extended-wavelength InGaAs photodetector %A Piccardo, Marco %A Noah A. Rubin %A Meadowcroft, Lauren %A Chevalier, Paul %A Yuan, Henry %A Kimchi, Joseph %A Federico Capasso %X We investigate the nonlinear optical response of a commercial extended-wavelength In0.81Ga0.19As uncooled photodetector. Degenerate two-photon absorption in the mid-infrared range is observed using a quantum cascade laser emitting at lambda = 4.5 lm as the excitation source. From the measured twophoton photocurrent signal, we extract a two-photon absorption coefficient beta((2)) = 0.660.2 cm/ MW, in agreement with the theoretical value obtained from the E-g(-3) scaling law. Considering the wide spectral range covered by extended-wavelength InxGa1-xAs alloys, this result holds promise for applications based on two-photon absorption for this family of materials at wavelengths between 1.8 and 5.6 mu m. Published by AIP Publishing. %B APPLIED PHYSICS LETTERS %I AMER INST PHYSICS %C 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA %V 112 %8 JAN 22 %G eng %N 4 %9 Article %R 10.1063/1.5018619 %0 Journal Article %J NATURE PHOTONICS %D 2018 %T Nano-optic endoscope for high-resolution optical coherence tomography in vivo %A Hamid Pahlevaninezhad %A Mohammadreza Khorasaninejad %A Yao-Wei Huang %A Zhujun Shi %A Lida P. Hariri %A David C. Adams %A Vivien Ding %A Alexander Zhu %A Cheng-Wei Qiu %A Federico Capasso %A Melissa J. Suter %X Acquisition of high-resolution images from within internal organs using endoscopic optical imaging has numerous clinical applications. However, difficulties associated with optical aberrations and the trade-off between transverse resolution and depth of focus significantly limit the scope of applications. Here, we integrate a metalens, with the ability to modify the phase of incident light at subwavelength level, into the design of an endoscopic optical coherence tomography catheter (termed nano-optic endoscope) to achieve near diffraction-limited imaging through negating non-chromatic aberrations. Remarkably, the tailored chromatic dispersion of the metalens in the context of spectral interferometry is utilized to maintain high-resolution imaging beyond the input field Rayleigh range, easing the trade-off between transverse resolution and depth of focus. We demonstrate endoscopic imaging in resected human lung specimens and in sheep airways in vivo. The combination of the superior resolution and higher imaging depth of focus of the nano-optic endoscope is likely to increase the clinical utility of endoscopic optical imaging. %B NATURE PHOTONICS %I NATURE PUBLISHING GROUP %C MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND %V 12 %P 540+ %8 SEP %G eng %N 9 %9 Article %R 10.1038/s41566-018-0224-2 %0 Journal Article %J OPTICS EXPRESS %D 2018 %T Polarization state generation and measurement with a single metasurface %A Noah A. Rubin %A Aun Zaidi %A Michael Juhl %A Ruo Ping Li %A J. P. BALTHASAR MUELLER %A Robert C. Devlin %A KRISTJAN LEOSSON %A Federico Capasso %X The constituent elements of metasurfaces may be designed with explicit polarization dependence, making metasurfaces a fascinating platform for new polarization optics. In this work we show that a metasurface grating can be designed to produce arbitrarily specified polarization states on a set of defined diffraction orders given that the polarization of the incident beam is known. We also demonstrate that, when used in a reverse configuration, the same grating may be used as a parallel snapshot polarimeter, requiring a minimum of bulk polarization optics. We demonstrate its use in measuring partially polarized light, and show that it performs favorably in comparison to a commercial polarimeter. This work is of consequence in any application requiring lightweight, compact, and low-cost polarization optics, polarimetry, or polarization imaging. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement %B OPTICS EXPRESS %I OPTICAL SOC AMER %C 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA %V 26 %P 21455-21478 %8 AUG 20 %G eng %N 17 %9 Article %R 10.1364/OE.26.021455 %0 Journal Article %J PHYSICAL REVIEW APPLIED %D 2018 %T Radiative Thermal Runaway Due to Negative-Differential Thermal Emission Across a Solid-Solid Phase Transition %A Bierman, David M. %A Lenert, Andrej %A Mikhail A. Kats %A Zhou, You %A Zhang, Shuyan %A De La Ossa, Matthew %A Ramanathan, Shriram %A Federico Capasso %A Wang, Evelyn N. %X Thermal runaway occurs when a rise in system temperature results in heat-generation rates exceeding dissipation rates. Here, we demonstrate that thermal runaway occurs in radiative (photon) systems given a sufficient level of negative-differential thermal emission. By exploiting the insulator-to-metal phase transition of vanadium dioxide, we show that a small increase in heat generation (e.g., 10 nW/mm(2)) results in a large change in surface temperature (e.g., similar to 35 K), as the thermal emitter switches from high emittance to low emittance. While thermal runaway is typically associated with catastrophic failure mechanisms, detailed understanding and control of this phenomenon may give rise to new opportunities in infrared sensing, camouflage, and rectification. %B PHYSICAL REVIEW APPLIED %I AMER PHYSICAL SOC %C ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA %V 10 %8 AUG 3 %G eng %N 2 %9 Article %R 10.1103/PhysRevApplied.10.021001 %0 Journal Article %J LIGHT-SCIENCE & APPLICATIONS %D 2018 %T Selective excitation and imaging of ultraslow phonon polaritons in thin hexagonal boron nitride crystals %A Antonio Ambrosio %A Michele Tamagnone %A Kundan Chaudhary %A Jauregui, Luis A. %A Philip Kim %A William L. Wilson %A Federico Capasso %X We selectively excite and study two new types of phonon-polariton guided modes that are found in hexagonal boron nitride thin flakes on a gold substrate. Such modes show substantially improved confinement and a group velocity that is hundreds of times slower than the speed of light, thereby providing a new way to create slow light in the midinfrared range with a simple structure that does not require nano-patterning. One mode is the fundamental mode in the first Restrahlen band of hexagonal boron nitride thin crystals on a gold substrate; the other mode is equivalent to the second mode of the second Restrahlen band of hexagonal boron nitride flakes that are suspended in vacuum. The new modes also couple efficiently with incident light at the hexagonal boron nitride edges, as we demonstrate experimentally using photo-induced force microscopy and scanning near-field optical microscopy. The high confinement of these modes allows for Purcell factors that are on the order of tens of thousands directly above boron nitride and a wide band, with new perspectives for enhanced light-matter interaction. Our findings demonstrate a new approach to engineering the dispersion of polaritons in 2D materials to improve confinement and light-matter interaction, thereby paving the way for new applications in mid-infrared nano-optics. %B LIGHT-SCIENCE & APPLICATIONS %I CHINESE ACAD SCIENCES, CHANGCHUN INST OPTICS FINE MECHANICS AND PHYSICS %C 3888, DONGNANHU ROAD, CHANGCHUN, 130033, PEOPLES R CHINA %V 7 %8 JUN 27 %G eng %9 Article %R 10.1038/s41377-018-0039-4 %0 Journal Article %J NANO LETTERS %D 2018 %T Single-Layer Metasurface with Controllable Multiwavelength Functions %A Zhujun Shi %A Mohammadreza Khorasaninejad %A Yao-Wei Huang %A Charles Roques-Carmes %A Alexander Y. Zhu %A Wei Ting Chen %A Vyshakh Sanjeev %A Zhao-Wei Ding %A Michele Tamagnone %A Kundan Chaudhary %A Robert C. Devlin %A Cheng-Wei Qiu %A Federico Capasso %K achromatic metalens %K Dispersion engineering %K metasurface %K orbital angular momentum states %K titanium dioxide %K Visible Spectrum %X In this paper, we report dispersion-engineered metasurfaces with distinct functionalities controlled by wavelength. Unlike previous approaches based on spatial multiplexing or vertical stacking of metasurfaces, we utilize a single phase profile with wavelength dependence encoded in the phase shifters' dispersion. We designed and fabricated a multiwavelength achromatic metalens (MAM) with achromatic focusing for blue (B), green (G), yellow (Y), and red (R) light and two wavelength-controlled beam generators (WCBG): one focuses light with orbital angular momentum (OAM) states (l = 0,1,2) corresponding to three primary colors; the other produces ordinary focal spots (l = 0) for red and green light, while generating a vortex beam (l = 1) in the blue. A full color (RGB) hologram is also demonstrated in simulation. Our approach opens a path to applications ranging from near-eye displays and holography to compact multiwavelength beam generation. %B NANO LETTERS %I AMER CHEMICAL SOC %C 1155 16TH ST, NW, WASHINGTON, DC 20036 USA %V 18 %P 2420-2427 %8 APR %G eng %N 4 %9 Article %R 10.1021/acs.nanolett.7b05458 %0 Journal Article %J APPLIED PHYSICS LETTERS %D 2018 %T Solid-immersion metalenses for infrared focal plane arrays %A Zhang, Shuyan %A Alexander Soibel %A Sam A. Keo %A Daniel Wilson %A Sir. B. Rafol %A David Z. Ting %A She, Alan %A Sarath D. Gunapala %A Federico Capasso %X Optical components based on metasurfaces (metalenses) offer an alternative methodology for microlens arrays. In particular, metalens arrays have the potential of being monolithically integrated with infrared focal plane arrays (IR FPAs) to increase the operating temperature and sensitivity of the latter. In this work, we demonstrate a type of transmissive metalens that focuses the incident light (lambda = 3-5 mu m) on the detector plane after propagating through the substrate, i.e., solid-immersion type of focusing. The metalens is fabricated by etching the backside of the detector substrate material (GaSb here), making this approach compatible with the architecture of back-illuminated FPAs. In addition, our designs work for all incident polarizations. We fabricate a 10 x 10 metalens array that proves the scalability of this approach for FPAs. In the future, these solid-immersion metalenses arrays will be monolithically integrated with IR FPAs. Published by AIP Publishing. %B APPLIED PHYSICS LETTERS %I AMER INST PHYSICS %C 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA %V 113 %8 SEP 10 %G eng %N 11 %9 Article %R 10.1063/1.5040395 %0 Journal Article %J APPLIED OPTICS %D 2018 %T Substrate aberration and correction for meta-lens imaging: an analytical approach %A Benedikt Groever %A Charles Roques-Carmes %A STEVEN J. BYRNES %A Federico Capasso %X Meta-lenses based on flat optics enabled a fundamental shift in lens production-providing an easier manufacturing process with an increase in lens profile precision and a reduction in size and weight. Here we present an analytical approach to correct spherical aberrations caused by light propagation through the substrate by adding a substrate-corrected phase profile, which differs from the original hyperbolic one. A meta-lens encoding the new phase profile would yield diffraction-limited focusing and an increase of up to 0.3 of its numerical aperture without changing the radius or focal length. In tightly focused laser spot applications such as direct laser lithography and laser printing, a substrate-corrected meta-lens can reduce the spatial footprint of the meta-lens. (C) 2018 Optical Society of America %B APPLIED OPTICS %I OPTICAL SOC AMER %C 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA %V 57 %P 2973-2980 %8 APR 20 %G eng %N 12 %9 Article %R 10.1364/AO.57.002973 %0 Journal Article %J PHYSICAL REVIEW LETTERS %D 2018 %T Three-Dimensional Measurement of the Helicity-Dependent Forces on a Mie Particle %A Liu, Lulu %A Di Donato, Andrea %A Ginis, Vincent %A Kheifets, Simon %A Amirzhan, Arman %A Federico Capasso %X Recently, it was shown that a Mie particle in an evanescent field ought to experience optical forces that depend on the helicity of the totally internally reflected beam. As yet, a direct measurement of such helicity-dependent forces has been elusive, as the widely differing force magnitudes in the three spatial dimensions place stringent demands on a measurement's sensitivity and range. In this study, we report the simultaneous measurement of all components of this polarization-dependent optical force by using a 3D force spectroscopy technique with femtonewton sensitivity. The vector force fields are compared quantitatively with our theoretical calculations as the polarization state of the incident light is varied and show excellent agreement. By plotting the 3D motion of the Mie particle in response to the switched force field, we offer visual evidence of the effect of spin momentum on the Poynting vector of an evanescent optical field. %B PHYSICAL REVIEW LETTERS %I AMER PHYSICAL SOC %C ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA %V 120 %8 MAY 31 %G eng %N 22 %9 Article %R 10.1103/PhysRevLett.120.223901 %0 Journal Article %J OPTICA %D 2018 %T Time-dependent population inversion gratings in laser frequency combs %A Piccardo, Marco %A Kazakov, Dmitry %A Noah A. Rubin %A Chevalier, Paul %A Wang, Yongrui %A Xie, Feng %A Lascola, Kevin %A Belyanin, Alexey %A Federico Capasso %X In standing-wave lasers, spatial hole burning induces a static grating of the population inversion, enabling multimode operation with several independent lasing modes. In the presence of a mode-locking mechanism, these modes may become correlated, giving origin to a frequency comb. Quantum cascade lasers, owing to their ultrafast gain dynamics, are ideally suited to achieve comb operation. Here we experimentally demonstrate that the modes of a quantum cascade laser frequency comb coherently beat to produce time-dependent population inversion gratings, which spatially modulate the current in the device at frequencies equal to the mode separation and its higher harmonics. This phenomenon allows the laser to serve as a phased collection of microwave local oscillators and is utilized to demonstrate quadrature amplitude modulation, a staple of modern communications. These findings may provide for a new class of integrated transmitters, potentially extending from the microwave to the low terahertz band. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement %B OPTICA %I OPTICAL SOC AMER %C 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA %V 5 %P 475-478 %8 APR 20 %G eng %N 4 %9 Article %R 10.1364/OPTICA.5.000475 %0 Journal Article %J PHYSICAL REVIEW APPLIED %D 2018 %T Topology-Optimized Multilayered Metaoptics %A Lin, Zin %A Benedikt Groever %A Federico Capasso %A Alejandro W. Rodriguez %A Loncar, Marko %X We propose a general topology-optimization framework for metasurface inverse design that can automatically discover highly complex multilayered metastructures with increased functionalities. In particular, we present topology-optimized multilayered geometries exhibiting angular phase control, including a single-piece nanophotonic metalens with angular aberration correction, as well as an angle-convergent metalens that focuses light onto the same focal spot regardless of the angle of incidence. %B PHYSICAL REVIEW APPLIED %I AMER PHYSICAL SOC %C ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA %V 9 %8 APR 20 %G eng %N 4 %9 Article %R 10.1103/PhysRevApplied.9.044030 %0 Journal Article %J ACS PHOTONICS %D 2018 %T Ultra-capacity Metasurfaces with Low Dimension and High Efficiency %A Cheng-Wei Qiu %A Zhang, Shuang %A Federico Capasso %A Kivshar, Yuri %B ACS PHOTONICS %I AMER CHEMICAL SOC %C 1155 16TH ST, NW, WASHINGTON, DC 20036 USA %V 5 %P 1640-1642 %8 MAY %G eng %N 5, SI %9 Editorial Material %R 10.1021/acsphotonics.8b00574 %0 Journal Article %J SCIENCE ADVANCES %D 2018 %T Ultra-confined mid-infrared resonant phonon polaritons in van der Waals nanostructures %A Michele Tamagnone %A Antonio Ambrosio %A Kundan Chaudhary %A Jauregui, Luis A. %A Philip Kim %A William L. Wilson %A Federico Capasso %X Hexagonal boron nitride has been proposed as an excellent candidate to achieve subwavelength infrared light manipulation owing to its polar lattice structure, enabling excitation of low-loss phonon polaritons with hyperbolic dispersion. We show that strongly subwavelength hexagonal boron nitride planar nanostructures can exhibit ultra-confined resonances and local field enhancement. We investigate strong light-matter interaction in these nanoscale structures via photo-induced force microscopy, scattering-type scanning near-field optical microscopy, and Fourier transform infrared spectroscopy, with excellent agreement with numerical simulations. We design optical nano-dipole antennas and directly image the fields when bright- or dark-mode resonances are excited. These modes are deep subwavelength, and strikingly, they can be supported by arbitrarily small structures. We believe that phonon polaritons in hexagonal boron nitride can play for infrared light a role similar to that of plasmons in noble metals at visible frequency, paving the way for a new class of efficient and highly miniaturized nanophotonic devices. %B SCIENCE ADVANCES %I AMER ASSOC ADVANCEMENT SCIENCE %C 1200 NEW YORK AVE, NW, WASHINGTON, DC 20005 USA %V 4 %8 JUN %G eng %N 6 %9 Article %R 10.1126/sciadv.aat7189 %0 Journal Article %J APPLIED PHYSICS LETTERS %D 2018 %T Watt-level widely tunable single-mode emission by injection-locking of a multimode Fabry-Perot quantum cascade laser %A Chevalier, Paul %A Piccardo, Marco %A Anand, Sajant %A Mejia, Enrique A. %A Wang, Yongrui %A Mansuripur, Tobias S. %A Xie, Feng %A Lascola, Kevin %A Belyanin, Alexey %A Federico Capasso %X Free-running Fabry-Perot lasers normally operate in a single-mode regime until the pumping current is increased beyond the single-mode instability threshold, above which they evolve into a multimode state. As a result of this instability, the single-mode operation of these lasers is typically constrained to few percents of their output power range, this being an undesired limitation in spectroscopy applications. In order to expand the span of single-mode operation, we use an optical injection seed generated by an external-cavity single-mode laser source to force the Fabry-Perot quantum cascade laser into a single-mode state in the high current range, where it would otherwise operate in a multimode regime. Utilizing this approach, we achieve single-mode emission at room temperature with a tuning range of 36 cm(-1) and stable continuous-wave output power exceeding 1W at 4.5 mu m. Far-field measurements show that a single transverse mode is emitted up to the highest optical power, indicating that the beam properties of the seeded Fabry-Perot laser remain unchanged as compared to free-running operation. Published by AIP Publishing. %B APPLIED PHYSICS LETTERS %I AMER INST PHYSICS %C 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA %V 112 %8 FEB 5 %G eng %N 6 %9 Article %R 10.1063/1.5018616 %0 Journal Article %J APPLIED PHYSICS LETTERS %D 2018 %T Widely tunable harmonic frequency comb in a quantum cascade laser %A Piccardo, Marco %A Chevalier, Paul %A Anand, Sajant %A Wang, Yongrui %A Kazakov, Dmitry %A Mejia, Enrique A. %A Xie, Feng %A Lascola, Kevin %A Belyanin, Alexey %A Federico Capasso %X Self-starting harmonic frequency combs in quantum cascade lasers exhibit skipping of several tens of longitudinal modes of the cavity, producing widely spaced frequency combs which may be used for a number of applications, such as the generation of high-spectral-purity microwave and terahertz tones. Under pure electrical injection, the spacing of such combs is fixed by fundamental laser parameters and can hardly be controlled. Here, we demonstrate that harmonic frequency combs in quantum cascade lasers can be induced by optical injection of an external seed provided by a tunable source. This scheme enables wide tunability of the harmonic comb spacing, allowing the skipping between 44 and 171 longitudinal modes in a single device. Published by AIP Publishing. %B APPLIED PHYSICS LETTERS %I AMER INST PHYSICS %C 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA %V 113 %8 JUL 16 %G eng %N 3 %9 Article %R 10.1063/1.5039611