## Recursos de colección

#### Caltech Authors (167.915 recursos)

Repository of works by Caltech published authors.

Group = Kavli Nanoscience Institute

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

Mujeeb-U-Rahman, Muhammad; Scherer, Axel
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...

2. #### 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...

3. #### 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....

4. #### 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...

5. #### 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...

6. #### 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...

7. #### 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...

8. #### 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.

9. #### 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...

10. #### 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...

11. #### 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...

12. #### 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...

13. #### 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...

14. #### 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...

15. #### Narrow-Linewidth Oxide-Confined Heterogeneously Integrated Si/III–V Semiconductor Lasers

Wang, Huolei; Kim, Dongwan; Harfouche, Mark; Santis, Christos T.; Satyan, Naresh; Rakuljic, George; Yariv, Amnon
We demonstrate a narrow-linewidth heterogeneously integrated Si/III-V laser, where the current confinement in the III-V structure is obtained by oxide isolation rather than by the prevailing ion-implantation technique. This method provides effective electrical isolation as well as III-V surface passivation, and a pathway for high-efficiency diode injection laser performance. This method also offers increased compatibility with potentially high-temperature annealing processes. The lasers shown here possess a threshold current of as low as 60 mA and a single-facet output power of more than 3 mW at 20 °C. A linewidth of 28 kHz at 1574.8 nm is obtained at a current...

16. #### Soliton microcomb operation to 778 nm

Yang, Q. F.; Lee, S. H.; Oh, D. Y.; Shen, B.; Wang, H.; Yang, K. Y.; Lai, Y. H.; Yi, X.; Vahala, K.
Soliton microcombs are demonstrated at both 1064 nm and 778 nm by dispersion-engineering on-chip silica resonators. These are the shortest wavelength soliton microcombs demonstrated to date and have potential applications in optical clocks and metrology.

17. #### Searching for Exoplanets Using a Microresonator Astrocomb

Suh, Myoung-Gyun; Yi, Xu; Lai, Yu-Hung; Leifer, S.; Grudinin, Ivan S.; Vasisht, G.; Martin, Emily C.; Fitzgerald, Michael P.; Doppmann, G.; Wang, J.; Mawet, D.; Papp, Scott B.; Diddams, Scott A.; Beichman, C.; Vahala, Kerry
Detection of weak radial velocity shifts of host stars induced by orbiting planets is an important technique for discovering and characterizing planets beyond our solar system. Optical frequency combs enable calibration of stellar radial velocity shifts at levels required for detection of Earth analogs. A new chip-based device, the Kerr soliton microcomb, has properties ideal for ubiquitous application outside the lab and even in future space-borne instruments. Moreover, microcomb spectra are ideally suited for astronomical spectrograph calibration and eliminate filtering steps required by conventional mode-locked-laser frequency combs. Here, for the calibration of astronomical spectrographs, we demonstrate an atomic/molecular line-referenced, near-infrared...

18. #### Soliton Microcomb Range Measurement

Suh, Myoung-Gyun; Vahala, Kerry
Laser-based range measurement systems are important in many application areas, including autonomous vehicles, robotics, manufacturing, formation flying of satellites, and basic science. Coherent laser ranging systems using dual-frequency combs provide an unprecedented combination of long range, high precision, and fast update rate. We report dual-comb distance measurement using chip-based soliton microcombs. A single pump laser was used to generate dual-frequency combs within a single microresonator as counterpropagating solitons. We demonstrated time-of-flight measurement with 200-nanometer precision at an averaging time of 500 milliseconds within a range ambiguity of 16 millimeters. Measurements at distances up to 25 meters with much lower precision...

19. #### Angle-Multiplexed Metasurfaces: Encoding Independent Wavefronts in a Single Metasurface under Different Illumination Angles

Kamali, Seyedeh Mahsa; Arbabi, Ehsan; Arbabi, Amir; Horie, Yu; Faraji-Dana, Mohammad Sadegh; Faraon, Andrei
The angular response of thin diffractive optical elements is highly correlated. For example, the angles of incidence and diffraction of a grating are locked through the grating momentum determined by the grating period. Other diffractive devices, including conventional metasurfaces, have a similar angular behavior due to the fixed locations of the Fresnel zone boundaries and the weak angular sensitivity of the meta-atoms. To alter this fundamental property, we introduce angle-multiplexed metasurfaces, composed of reflective high-contrast dielectric U-shaped meta-atoms, whose response under illumination from different angles can be controlled independently. This enables flat optical devices that impose different and independent optical...

20. #### Stabilization of hybrid perovskite CH_3NH_3PbI_3 thin films by graphene passivation

Tseng, Wei-Shiuan; Jao, Meng-Huan; Hsu, Chen-Chih; Huang, Jing-Shun; Wu, Chih-I.; Yeh, N.-C.
We report the long-term stability of water-sensitive hybrid perovskites CH_3NH_3PbI_3 that were protected with monolayer graphene. This successful passivation was enabled by our development of a new water-free and polymer-free graphene transfer method. Monolayer graphene samples grown by plasma-enhanced chemical vapor deposition and transferred onto different substrates with the water/polymer-free method were found to preserve their high-quality characteristics after the transfer, as manifested by the studies of Raman, X-ray and ultraviolet photoemission spectroscopy (XPS and UPS), optical absorption, and sheet resistance. Additionally, XPS, UPS and optical absorption studies of fully graphene-covered CH_3NH_3PbI_3 thin films showed spectral invariance even after 3...

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