## Recursos de colección

#### Caltech Authors (171.365 recursos)

Repository of works by Caltech published authors.

Group = Kavli Nanoscience Institute

1. #### Ultralow Thermal Conductivity and Mechanical Resilience of Architected Nanolattices

Dou, Nicholas G.; Jagt, Robert A.; Portela, Carlos M.; Greer, Julia R.; Minnich, Austin J.
Creating materials that simultaneously possess ultralow thermal conductivity, high stiffness, and damage tolerance is challenging because thermal and mechanical properties are coupled in most fully dense and porous solids. Nanolattices can fill this void in the property space because of their hierarchical design and nanoscale features. We report that nanolattices composed of 24- to 182-nm-thick hollow alumina beams in the octet-truss architecture achieved thermal conductivities as low as 2 mW m^(–1) K^(–1) at room temperature while maintaining specific stiffnesses of 0.3 to 3 MPa kg^(–1) m^3 and the ability to recover from large deformations. These nanoarchitected materials possess the same...

2. #### Two-photon microscopy with a double-wavelength metasurface objective lens

Arbabi, Ehsan; Li, Jiaqi; Hutchins, Romanus J.; Kamali, Seyedeh Mahsa; Arbabi, Amir; Horie, Yu; Van Dorpe, Pol; Gradinaru, Viviana; Wagenaar, Daniel A.; Faraon, Andrei
Two-photon microscopy is a key imaging technique in life sciences due to its superior deep-tissue imaging capabilities. Light-weight and compact two-photon microscopes are of great interest because of their applications for in vivo deep brain imaging. Recently, dielectric metasurfaces have enabled a new category of small and light-weight optical elements, including objective lenses. Here we experimentally demonstrate two-photon microscopy using a double-wavelength metasurface lens. It is specifically designed to focus 820-nm and 605-nm light, corresponding to the excitation and emission wavelengths of the measured fluorophors, to the same focal distance. The captured two-photon images are qualitatively comparable to the ones...

3. #### Full Stokes imaging polarimetry using dielectric metasurfaces

Arbabi, Ehsan; Kamali, Seyedeh Mahsa; Arbabi, Amir; Faraon, Andrei
Polarization is a degree of freedom of light carrying important information that is usually absent in intensity and spectral content. Imaging polarimetry is the process of determining the polarization state of light, either partially or fully, over an extended scene. It has found several applications in various fields, from remote sensing to biology. Among different devices for imaging polarimetry, division of focal plane polarization cameras (DoFP-PCs) are more compact, less complicated, and less expensive. In general, DoFP-PCs are based on an array of polarization filters in the focal plane. Here we demonstrate a new principle and design for DoFP-PCs based...

4. #### Characterization of ^(171)Yb^(3+):YVO_4 for photonic quantum technologies

Kindem, Jonathan M.; Bartholomew, John G.; Woodburn, Philip J. T.; Zhong, Tian; Craiciu, Ioana; Cone, Rufus L.; Thiel, Charles W.; Faraon, Andrei
Rare-earth ions in crystals are a proven solid-state platform for quantum technologies in the ensemble regime and attractive for new opportunities at the single-ion level. Among the trivalent rare earths, ^(171)Yb^(3+) is unique in that it possesses a single 4f excited-state manifold and is the only paramagnetic isotope with a nuclear spin of 1/2. In this work, we present measurements of the optical and spin properties of ^(171)Yb^(3+):YVO_4 to assess whether this distinct energy-level structure can be harnessed for quantum interfaces. The material was found to possess large optical absorption compared to other rare-earth-doped crystals owing to the combination of...

5. #### Controlling rare-earth ions in a nanophotonic resonator using the ac Stark shift

Bartholomew, John G.; Zhong, Tian; Kindem, Jonathan M.; Lopez-Rios, Raymond; Rochman, Jake; Craiciu, Ioana; Miyazono, Evan; Faraon, Andrei
On-chip nanophotonic cavities will advance quantum information science and measurement because they enable efficient interaction between photons and long-lived solid-state spins, such as those associated with rare-earth ions in crystals. The enhanced photon-ion interaction creates new opportunities for all-optical control using the ac Stark shift. Toward this end, we characterize the ac Stark interaction between off-resonant optical fields and Nd^(3+)-ion dopants in a photonic crystal resonator fabricated from yttrium orthovanadate (YVO_4). Using photon echo techniques, at a detuning of 160 MHz we measure a maximum ac Stark shift of 2π × 12.3 MHz per intracavity photon, which is large compared...

6. #### Two dimensional optomechanical crystals for quantum optomechanics

Pfeifer, Hannes; Ren, Hengjiang; MacCabe, Greg; Painter, Oskar
Cooling of nanomechanical resonators to their motional ground state [1, 2] triggered recent achievements like non-classical mechanical state preparation [3] or coherent optical to microwave photon conversion [4]. Implementations of such system with optomechanical crystal (OMC) resonators use the co-localization of optical and acoustic modes in a periodically patterned device layer of a silicon-on-insulator (SOI) chip. An initialization of mechanical resonator to low thermal occupations is required by most quantum optomechanical operations. Reaching small thermal mechanical mode occupations and mechanical Q-factors ≳ 10^6 requires pre-cooling to millikelvin temperatures, where even weak optical absorption induces unfavorable local heating [5]. Commonly used...

7. #### Universal isocontours for dissipative Kerr solitons

Li, Xinbai; Shen, Boqiang; Wang, Heming; Yang, Ki Youl; Yi, Xu; Yang, Qi-Fan; Zhou, Zhiping; Vahala, Kerry
Dissipative Kerr solitons can be generated within an existence region defined on a space of normalized pumping power versus cavity-pump detuning frequency. The contours of constant soliton power and constant pulse width in this region are studied through measurement and simulation. Such isocontours impart structure to the existence region and improve understanding of soliton locking and stabilization methods. As part of the study, dimensionless, closed-form expressions for soliton power and pulse width are developed (including Raman contributions). They provide isocontours in close agreement with those from the full simulation, and, as universal expressions, can simplify the estimation of soliton properties...

8. #### Enhanced photon-phonon coupling via dimerization in one-dimensional optomechanical crystals

Matheny, Matthew H.
We show that dimerization of an optomechanical crystal lattice, which leads to folding of the band diagram, can couple flexural mechanical modes to optical fields within the unit cell via radiation pressure. When compared to currently realized crystals, a substantial improvement in the coupling between photons and phonons is found. For experimental verification, we implement a dimerized lattice in a silicon optomechanical nanobeam cavity and measure a vacuum coupling rate of g_0/2π= 1.7 MHz between an optical resonance at λ_c = 1545 nm and a mechanical resonance at 1.14 GHz.

9. #### Optimization Techniques for Miniaturized Integrated Electrochemical Sensors

Electrochemical sensors are integral components of various integrated sensing applications. In this work, we provide details of optimizing electrochemical sensors for CMOS compatible integrated designs at sub-mm size scales. The focus is on optimization of electrode materials and geometry. We provide design details for both working electrode and reference electrode materials for hydrogen peroxide sensing applications which form the basis for many metabolic sensors. We also present results on geometrical variations in designing such sensors and demonstrate that such considerations are very relevant for optimizing the overall sensor performance. We also present results for such optimized sensors on actual CMOS...

10. #### Fabrication of Patterned Integrated Electrochemical Sensors

Fabrication of integrated electrochemical sensors is an important step towards realizing fully integrated and truly wireless platforms for many local, real-time sensing applications. Micro/nanoscale patterning of small area electrochemical sensor surfaces enhances the sensor performance to overcome the limitations resulting from their small surface area and thus is the key to the successful miniaturization of integrated platforms. We have demonstrated the microfabrication of electrochemical sensors utilizing top-down lithography and etching techniques on silicon and CMOS substrates. This choice of fabrication avoids the need of bottom-up techniques that are not compatible with established methods for fabricating electronics (e.g., CMOS) which form...

11. #### Dual-Gated Active Metasurface at 1550 nm with Wide (>300°) Phase Tunability

Shirmanesh, Ghazaleh Kafaie; Sokhoyan, Ruzan; Pala, Ragip A.; Atwater, Harry A.
Active metasurfaces composed of electrically reconfigurable nanoscale subwavelength antenna arrays can enable real-time control of scattered light amplitude and phase. Achievement of widely tunable phase and amplitude in chip-based active metasurfaces operating at or near 1550 nm wavelength has considerable potential for active beam steering, dynamic hologram rendition, and realization of flat optics with reconfigurable focal lengths. Previously, electrically tunable conducting oxide-based reflectarray metasurfaces have demonstrated dynamic phase control of reflected light with a maximum phase shift of 184° ( Nano Lett. 2016, 16, 5319). Here, we introduce a dual-gated reflectarray metasurface architecture that enables much wider (>300°) phase tunability....

12. #### Bridging ultrahigh-Q devices and photonic circuits

Yang, Ki Youl; Oh, Dong Yoon; Lee, Seung Hoon; Yang, Qi-Fan; Yi, Xu; Shen, Boqiang; Wang, Heming; Vahala, Kerry
Optical microresonators are essential to a broad range of technologies and scientific disciplines. However, many of their applications rely on discrete devices to attain challenging combinations of ultra-low-loss performance (ultrahigh Q) and resonator design requirements. This prevents access to scalable fabrication methods for photonic integration and lithographic feature control. Indeed, finding a microfabrication bridge that connects ultrahigh-Q device functions with photonic circuits is a priority of the microcavity field. Here, an integrated resonator having a record Q factor over 200 million is presented. Its ultra-low-loss and flexible cavity design brings performance to integrated systems that has been the exclusive domain...

13. #### Subradiant states of quantum bits coupled to a one-dimensional waveguide

Albrecht, Andreas; Henriet, Loïc; Asenjo-Garcia, Ana; Dieterle, Paul B.; Painter, Oskar; Chang, Darrick E.
The properties of coupled emitters can differ dramatically from those of their individual constituents. Canonical examples include sub- and super-radiance, wherein the decay rate of a collective excitation is reduced or enhanced due to correlated interactions with the environment. Here, we systematically study the properties of collective excitations for regularly spaced arrays of quantum emitters coupled to a one-dimensional (1D) waveguide. We find that, for low excitation numbers, the modal properties are well-characterized by spin waves with a definite wavevector. Moreover, the decay rate of the most subradiant modes obeys a universal scaling with a cubic suppression in the number...

14. #### Superconducting metamaterials for waveguide quantum electrodynamics

Mirhosseini, Mohammad; Kim, Eunjong; Ferreira, Vinicius S.; Kalaee, Mahmoud; Sipahigil, Alp; Keller, Andrew J.; Painter, Oskar
The embedding of tunable quantum emitters in a photonic bandgap structure enables the control of dissipative and dispersive interactions between emitters and their photonic bath. Operation in the transmission band, outside the gap, allows for studying waveguide quantum electrodynamics in the slow-light regime. Alternatively, tuning the emitter into the bandgap results in finite range emitter-emitter interactions via bound photonic states. Here we couple a transmon qubit to a superconducting metamaterial with a deep sub-wavelength lattice constant ($\lambda/60$). The metamaterial is formed by periodically loading a transmission line with compact, low loss, low disorder lumped element microwave resonators. We probe the coherent and dissipative dynamics of the system by measuring the...

15. #### MEMS-tunable dielectric metasurface lens

Arbabi, Ehsan; Arbabi, Amir; Kamali, Seyedeh Mahsa; Horie, Yu; Faraji-Dana, Mohammad Sadegh; Faraon, Andrei
Varifocal lenses, conventionally implemented by changing the axial distance between multiple optical elements, have a wide range of applications in imaging and optical beam scanning. The use of conventional bulky refractive elements makes these varifocal lenses large, slow, and limits their tunability. Metasurfaces, a new category of lithographically defined diffractive devices, enable thin and lightweight optical elements with precisely engineered phase profiles. Here we demonstrate tunable metasurface doublets, based on microelectromechanical systems (MEMS), with more than 60 diopters (about 4%) change in the optical power upon a 1-μm movement of one metasurface, and a scanning frequency that can potentially reach...

16. #### Gigahertz-repetition-rate soliton microcombs

Suh, Myoung-Gyun; Vahala, Kerry
Soliton microcombs with repetition rates as low as 1.86 GHz are demonstrated, thereby entering a regime more typical of table–top combs. Low rates are important in spectroscopy and relax requirements on comb processing electronics.

17. #### Bridging ultra-high-Q devices and photonic circuits

Yang, Ki Youl; Oh, Dong Yoon; Lee, Seung Hoon; Yang, Qi-Fan; Yi, Xu; Vahala, Kerry
Optical microcavities are essential in numerous technologies and scientific disciplines. However, their application in many areas relies exclusively upon discrete microcavities in order to satisfy challenging combinations of ultra-low-loss performance (high cavity-Q-factor) and cavity design requirements. Indeed, finding a microfabrication bridge connecting ultra-high-Q device functions with micro and nanophotonic circuits has been a long-term priority of the microcavity field. Here, an integrated ridge resonator having a record Q factor over 200 million is presented. Its ultra-low-loss and flexible cavity design brings performance that has been the exclusive domain of discrete silica and crytalline microcavity devices to integrated systems. Two distinctly...

18. #### Bridging ultra-high-Q devices and photonic circuits

Yang, Ki Youl; Oh, Dong Yoon; Lee, Seung Hoon; Yang, Qi-Fan; Yi, Xu; Vahala, Kerry
Optical microcavities are essential in numerous technologies and scientific disciplines. However, their application in many areas relies exclusively upon discrete microcavities in order to satisfy challenging combinations of ultra-low-loss performance (high cavity-Q-factor) and cavity design requirements. Indeed, finding a microfabrication bridge connecting ultra-high-Q device functions with micro and nanophotonic circuits has been a long-term priority of the microcavity field. Here, an integrated ridge resonator having a record Q factor over 200 million is presented. Its ultra-low-loss and flexible cavity design brings performance that has been the exclusive domain of discrete silica and crytalline microcavity devices to integrated systems. Two distinctly...

19. #### Complex wavefront engineering with disorder-engineered metasurfaces

Jang, Mooseok; Horie, Yu; Shibukawa, Atsushi; Brake, Joshua; Liu, Yan; Kamali, Seyedeh Mahsa; Arbabi, Amir; Ruan, Haowen; Faraon, Andrei; Yang, Changhuei
Recently, complex wavefront engineering with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics. These capabilities include extended volume, aberration-free focusing and subwavelength focusing via evanescent mode coupling. However, translating these capabilities to useful applications has remained challenging as the input-output characteristics of the disordered media (P variables) need to be exhaustively determined via O(P) measurements. Here, we propose a paradigm shift where the disorder is specifically designed so that its exact characteristics are known, resulting in an a priori determined transmission matrix that can be utilized with only a few alignment steps. We implement this concept...

20. #### Optical magnetism in planar metamaterial heterostructures

Papadakis, Georgia T.; Fleischman, Dagny; Davoyan, Artur; Yeh, Pochi; Atwater, Harry A.
Harnessing artificial optical magnetism has previously required complex two- and three-dimensional structures, such as nanoparticle arrays and split-ring metamaterials. By contrast, planar structures, and in particular dielectric/metal multilayer metamaterials, have been generally considered non-magnetic. Although the hyperbolic and plasmonic properties of these systems have been extensively investigated, their assumed non-magnetic response limits their performance to transverse magnetic (TM) polarization. We propose and experimentally validate a mechanism for artificial magnetism in planar multilayer metamaterials. We also demonstrate that the magnetic properties of high-index dielectric/metal hyperbolic metamaterials can be anisotropic, leading to magnetic hyperbolic dispersion in certain frequency regimes. We show that...

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