Nathaniel Kinsey, Ph.D.

Taking Advantage of (Plasmonic) Loss

Optics & Photonics News  online

2018-05-01

The work was conducted by the research groups led by OSA Fellows Juerg Leuthold at ETH Zürich, Larry Dalton at the University of Washington, and Vladimir Shalaev and Alexandra Boltasseva at Purdue, and co-conceived by OSA members Christian Haffner of ETH Zürich and Nathaniel Kinsey of Virginia Commonwealth.

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Switch controls light on a nanoscale for faster information processing

Purdue  online

2018-04-25

Haffner and Nathaniel Kinsey, former Purdue student and now a professor of electrical and computer engineering at Virginia Commonwealth University, along with Leuthold, Shalaev and Boltasseva, conceived the idea of a low-loss plasmon assisted electro-optic modulator for subwavelength optical devices, including compact on-chip sensing and communications technologies.

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VCU Engineering Researcher Receives Air Force Research Award to Study How Light Interacts with — and Changes — Materials

Phys.org  online

2018-01-25

Lasers, Blu-ray players and Google cars are just a few of the technologies that operate using light waves. Specialty materials with enhanced optical properties can streamline the design of these and other devices and make them work more efficiently. With an Air Force Office of Scientific Research (AFOSR) grant, Nathaniel Kinsey, Ph.D., assistant professor in the Department of Electrical and Computer Engineering at the VCU School of Engineering, is conducting research to develop optically enhanced materials. Kinsey is using his award to study how intense light interacts with matter, a discipline called nonlinear optics. The optical response of a material usually scales linearly with the amplitude of the electric field—in Kinsey's research, the light—that is applied to it. At high intensities of light, the material properties can change rapidly and lead to interesting and useful nonlinear effects. These effects, however, are generally weak. To see how materials can be designed to elicit stronger optical responses, Kinsey and his team are studying the properties of various oxides that are engineered at the atomic level. Working layer by layer, they are adding aluminum electrons to zinc oxide, for example— a process called doping. This process creates a unique material transition within the transparent oxide. At one frequency, the doped material behaves like a metal. At another, it acts like a dielectric, a superior supporter of electrostatic fields. This effect produces a property called epsilon-near-zero (ENZ), which has been shown to enhance nonlinear optical effects. "Photons don't normally want to interact, but by enhancing the nonlinearities, we are making them do so more efficiently," Kinsey said. The benefit of these effects is greater energy efficiency in technologies including lasers and fiber optics. The oxides Kinsey is working with can be doped more than other materials, producing an ENZ property that aligns with the frequencies of light used for fiber optic communications.

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A Platform for Practical Plasmonics

SPIE Newsroom  online

2017-01-04

Materials that are compatible with standard processing techniques can be used for waveguides and modulators without sacrificing performance and functionality.

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'Plasmonics' could lead to super-fast optic communications

Engadget  

2015-08-03

Researchers at Purdue University have developed a new kind of material that could improve the speed of optical communications by as much as 5000 times the current state of the art. The material is made of aluminum-doped zinc oxide (AZO) and it is able to change the amount of light it reflects by up to 40 percent while consuming a fraction of the power that conventional optical semiconductors consume. By reflecting more or less light, the material can encode and transmit data. What's more, this material operates in the near-infrared spectrum range, which is what is most commonly used in optical communications.

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Optical transistor will be faster than CMOS devices

Electronics Weekly  

2015-08-06

The team at Purdue University claim that the so-called “plasmonic oxide material” could make possible devices for optical communications that are at least 10 times faster than conventional technologies.

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'Plasmonic' material could bring ultrafast all-optical communications

Purdue University News  

2015-07-30

Researchers have created a new "plasmonic oxide material" that could make possible devices for optical communications that are at least 10 times faster than conventional technologies.

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Integrated Nanophotonics

This projects aims to take advantage of the large bandwidth of optics to push the limits of communication systems. The design and fabrication of passive and active devices is exercised to explore the limits of hybrid electronic/photonic/plasmonic systems.

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Nonlinear Optics

This project is focused on the study of fundamental optical nonlinearities in new materials such as the transition metal nitrides and the transparent conducting oxides. We observe ultrafast and strong effects which may be useful for developing all-optical logic and tunable/dynamic metamaterials.

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Solar-cell efficiency enhancement using metasurfaces

US 14/454,709

2015-02-12

A solar-energy module is disclosed. The module includes a first electrode configured to receive incident visible light with a different refractive index than the medium through which light travels prior to becoming incident on the first electrode, the first electrode having a first metasurface arrangement formed through the first electrode, and configured to selectively i) match the optical impedances of the first electrode and the medium, and ii) cause light to be refracted substantially away from normal refraction angle, a photon-absorbing material coupled to the first electrode on a first surface of the photon-absorbing material and configured to receive refracted light through the first electrode and adapted to produce an electrical current in response to the refracted light, length of the photon absorbing material substantially larger than thickness of the photon-absorbing material, and a second electrode coupled to the photon-absorbing material on a second surface of the photon-absorbing material.

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Light-source efficiency enhancement using metasurfaces

US 61/862,999

2015-02-12

A light source includes a photon generator adapted to provide light at a wavelength and a metasurface disposed over a surface of the generator, thinner than the wavelength of the emitted first light and including a plurality of nanoantennas. The surface can be for outcoupling or reflection. Each of the nanoantennas has dimensions less than the wavelength of the light and includes at least one region. The region can be a region of dielectric material arranged between two regions of conductive material so that a displacement current path is defined that crosses the region of the dielectric material, or a region of conductive material arranged between two regions of dielectric material so that a conductive current path is defined that crosses the region of the conductive material.

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Optically activated linear switch for radar limiters or high power switching applications

US 14/421,412

2015-07-06

The present invention relates to a solid-state optically activated switch that may be used as limiting switch in a variety of applications or as a high voltage switch. In particular, the switch may incorporate the photoconductive properties of a semiconductor to provide the limiting function in a linear mode. In one embodiment, a configuration of the switch allows for greater than 99.9999% off-state transmission and an on-state limiting of less than 0.0001% of the incident signal.

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EGRE 309 Intro. to Electromangetic Fields

This course provides an introduction to the concept of electromagnetic fields. Topics include electrostatics, magnetostatics, scalar and vector potentials, and work and energy in fields, as well as the analysis and understanding of the phenomena associated with static electric and magnetic fields. Laboratory exercises will serve to reinforce students’ understanding of fields and train them in methods to measure, quantify and analyze electromagnetic phenomena. Course Contents: 1. Review of vector, differential, and integral calculus 2. Electric Field, Electric Potential, Work and Energy in Electrostatics, Laplace Equation, Separation of Variables, Method of Images, Polarization, Electric Displacement, Dielectrics 3. Lorentz Force, Divergence and Curl of B, Biot-Savart Law, Magnetic Vector Potential, Magnetization, Conservation Laws The class is supplemented with numerical simulation projects using COMSOL Multiphysics to aid the visualization and understanding of electromagnetic fields.

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EGRE 310 Electromagnetic Fields and Waves

This course covers the fundamentals of time-varying electromagnetic fields. Topics include electromagnetic induction, Maxwell’s equations, wave propagation, guided waves, transmission lines and antennas. Laboratory exercises will serve to reinforce students’ understanding of time-varying fields and waves and train them in methods to measure, quantify and analyze dynamic electromagnetic phenomena. Course Contents: 1. Faraday's Law, Magnetic Circuits, Transformers and Motional Electromotive Force 2. Displacement Current and Final Maxwell's Equations 3. Time Harmonic Fields and Potentials, Electromagnetic Waves, Wave Propagation, Polarization, and Reflection 4. Transmission Lines, Smith Chart, Microstrip Lines and Data Cables 5. Wave Propagation in a Guide, Rectangular Waveguides, Waveguide Resonators 6. Dipole Antennas, Antenna Characteristics, Radar Equation and Friis Equation

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EGRE 525 Fundamentals of Photonics Engineering

Course Description: In this course we will cover the basics of linear optical systems and materials. We will begin with an overview of optical materials and the models used to describe their response, with an emphasis on the physical processes that give rise to these responses. Following, we will discuss the basics of linear or geometric optics, covering linear light propagation through media as well as the operational principles of specific components such as cavities, polarizers, phase plates, and interferometers. Course Contents: 1. Review of electromagnetic fields and wave propagation as well as semiconductor band theory 2. Optical coefficients: refractive index, permittivity, and linear susceptibility 3. Models of dielectric materials: Lorentz oscillator, Kramers-Kronig relations, and dispersion 4. Absorption and luminescence of materials 5. Models of metallic materials: Drude oscillator, doped semiconductors, and plasmons 6. Propagation of light in materials: Reflection, refraction, scattering 7. Geometric optics: lenses, mirrors, prisms, ABCD matrices 8. Polarization of light & devices: polarizers, dichroism, birefringence, optical activity 9. Interference of light and applications Time permitting, additional topics may include experimental optical systems (pump-probe, Michelson interferometer, ellipsometry, etc.) active optical effects (liquid crystals & modulators), ultrafast optical phenomena, Fourier optics, and/or plasmonics & metamaterials.

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EGRE 624 Nonlinear Optical Materials and Devices

This course describes the principles of nonlinear optics and discusses the operation of photonic devices and systems that utilize various second- and third-order nonlinear optical effects. The topics include electromagnetic wave propagation in anisotropic media, nonlinear optical susceptibility tensor, linear and quadratic electro-optic effects, second harmonic, sum- and difference-frequency generation, phase-matching, parametric amplification, optical switching, multi-photon absorption, and self-focusing and self-phase modulation. Course Contents: Review: Electromagnetic wave propagation in media Electromagnetic wave propagation in anisotropic media, dielectric tensor Index ellipsoid, birefringence, uniaxial and biaxial crystals Nonlinear optical susceptibility tensor, nonlinear materials, symmetry Maxwell’s equations in nonlinear media, Coupled-Wave theory and density matrix formalism (very brief) Second-order optical nonlinearities Second-harmonic generation, sum-frequency generation (up-conversion), difference frequency generation (down-conversion), optical rectification Phase matching, methods to achieve phase matching Optical Parametric Amplifier, Optical Parametric Oscillator Linear electro-optic effect (Pockels effect), Electrooptic modulators Third-order optical nonlinearities Third-order nonlinear susceptibility Third harmonic generation Intensity dependent refractive index, Kerr effect Self-focusing, self-phase modulation Optical phase conjugation Optical bistability, optical switching Two-photon absorption Semiconductor nonlinearities Quadratic electro-optic effect Four-wave mixing Measurement methods for nonlinear susceptibilities

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EGRE 627 Nanophotonics

Advances in nanotechnology and fabrication have allowed scientists to control light like never before, bringing topics of science fiction like cloaking, unlimited resolution imaging, nanometer thick optics, and breakthrough treatments for disease into the realm of reality. This class will explore what is possible when you can confine light at the nanoscale and engineer materials at will, covering topics such as light guiding by metals (plasmonics), optical lattices (photonic crystals), arbitrary materials (meta-materials/surfaces), nanoscale lasers (spasers), and stopping light (static optics). Students will be exposed to the newest advances in the field through discussion, projects, and presentations. Course Contents: Review of Electromagnetic Waves, Guides, Cavities Review of Dispersion and Optical Properties of Metals/Dielectrics Conservation of Momentum, K-Space Diagrams, Isofrequency Curves Bulk metamaterials, effective medium theory, and transformation optics Surface Plasmon Polariton Waves and Excitation Approaches SPP Waveguide Structures and the Confinement/Loss Trade-off Localized Surface Plasmons and Plasmonic Resonances Plasmonic Nanoantennas, Electric & Magnetic Resonances, Negative Refraction and Negative Index Babinet Principle, Extraordinary Transmission Generalized Snell’s Law and Metasurfaces: Lenses, Cloaks, etc. Dielectric Metasurfaces, Mie Resonances Time Permitting – based on class interest Photonic Crystals, Optical Bandgaps, Slow Light Photonic Crystal Fibers Epsilon Near Zero and Near Zero Index Materials Surface Plasmon Lasers Near field imaging Enhanced nonlinearities Control of Emission and Purcell Effect

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EGRE 691 Quantum Optics

As quantum mechanical concepts are put to the test, optics has become a critical link in the chain of discovering new effects and developing new technologies. From powering ultrasensitive detectors (like LIGO), the quest for the general quantum computer, and state control of single atoms, photons are excellent for transferring information between quantum systems. In this course, we will explore many facets of the vast world of quantum optics providing an introduction to topics such as field quantization, coherent photon states, quantum description of linear processes (emission/radiation/interference/beam splitters), squeezed states, cavity electrodynamics, and quantum information processing. The course will include numerous references and examples for recent and cutting-edge science in this rapidly developing field. Students will be encouraged to explore new thought-provoking ideas to stretch their capabilities, and develop these ideas through research reports, presentations, and project proposals. Course Contents: Brief review of quantum mechanics: wavefunctions, operators, Hamiltonians, Dirac notation, standard problems Field quantization: single/multi-mode quantized fields, vacuum fluctuations, quantum phase Coherent states: eigenstates of annihilation operation, phase space description Emission and absorption by atoms: atom-field interactions, Rabi model, Jaynes-Cummings model, dressed states Quantum coherence: classical/quantum coherence, Young’s interference Beam splitters and interferometers: single photon experiments, quantum description of beam splitters, interference with coherent states Non-classical light: squeezed states, photon anti-bunching, cat states *Dissipative interactions: Decoherence and effects *Optical test of quantum mechanics: photon sources, HOM interference, quantum eraser, superluminal tunneling Experiments in cavity QED: Rydberg atoms, creating entangled atoms in CQED Applications of entanglement: entanglement and interferometric measurements, quantum teleportation, cryptography, random number generator, quantum gates*Topics may be removed based on time available

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Near-zero-index materials for photonics

2019-09-01

The discovery, design and development of materials are critically linked to advances in many areas of research, and optics is no exception. Recently, the spectral region in which the index of refraction of a material approaches zero has become a topic of interest owing to fascinating phenomena, such as static light, enhanced nonlinearities, light tunnelling and emission tailoring. As a result, such near-zero-index (NZI) materials bridge materials development and optical research. Here, we review recent advances in various classes of NZI platforms, with particular focus on homogeneous materials, including metals, semi-metals, doped semiconductors, phononic and interband materials, discussing the novel optical phenomena that they can produce. We also overview the developments in a key area for NZI materials, nonlinear optics, and survey some of the future goals in the field, such as the development of tailorable NZI materials in the visible range and the improvement of the theoretical description of the nonlinear enhancements in these materials.

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Epsilon-near-zero Al-doped ZnO for ultrafast switching at telecom wavelengths

2015 Transparent conducting oxides have recently gained great attention as CMOS-compatible materials for applications in nanophotonics due to their low optical loss, metal-like behavior, versatile/tailorable optical properties, and established fabrication procedures. In particular, aluminum-doped zinc oxide (AZO) is very attractive because its dielectric permittivity can be engineered over a broad range in the near-IR and IR. However, despite all these beneficial features, the slow (>100  ps>100  ps) electron-hole recombination time typical of these compounds still represents a fundamental limitation impeding ultrafast optical modulation. Here we report the first epsilon-near-zero AZO thin films that simultaneously exhibit ultrafast carrier dynamics (excitation and recombination time below 1 ps) and an outstanding reflectance modulation up to 40% for very low pump fluence levels (

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Fast and Slow Nonlinearities in Epsilon‐Near‐Zero Materials

2021-08-02

Novel materials, with enhanced light–matter interaction capabilities, play an essential role in achieving the lofty goals of nonlinear optics. Recently, epsilon‐near‐zero (ENZ) media have emerged as a promising candidate to enable the enhancement of several nonlinear processes including refractive index modulation and harmonic generation. Here, the optical nonlinearity of ENZ media is analyzed to clarify the commonalities with other nonlinear media and its unique properties. Transparent conducting oxides as the family of ENZ media with near‐zero permittivity in the near‐infrared (telecom) band are focused on. The instantaneous and delayed nonlinearities are investigated. By identifying their common origin from the band nonparabolicity, it is shown that their relative strength is entirely determined by a ratio of the energy and momentum relaxation (or dephasing) times. Using this framework, ENZ materials are compared against the many promising nonlinear media that are investigated in literature and show that while ENZ materials do not radically outpace the strength of traditional materials in either the fast or slow nonlinearity, they pack key advantages such as an ideal response time, intrinsic slow light enhancement, and broadband nature in a compact platform making them a valuable tool for ultrafast photonics applications for decades to come.

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Absorptive loss and band non-parabolicity as a physical origin of large nonlinearity in epsilon-near-zero materials

2021-08-02

For decades, nonlinear optics has been used to control the frequency and propagation of light in unique ways enabling a wide range of applications such as ultrafast lasing, sub-wavelength imaging, and novel sensing methods. Through this, a key thread of research in the field has always been the development of new and improved nonlinear materials to empower these applications. Recently, epsilon-near-zero (ENZ) materials have emerged as a potential platform to enhanced nonlinear interactions, bolstered in large part due to the extreme refractive index tuning (Δn∼ 0.1 - 1) of sub-micron thick films that has been demonstrated in literature. Despite this experimental success, the theory has lagged and is needed to guide future experimental efforts. Here, we construct a theoretical framework for the intensity-dependent refractive index of the most popular ENZ materials, heavily doped semiconductors. We demonstrate that the nonlinearity when excited below bandgap, is due to the modification of the effective mass of the electron sea which produces a shift in the plasma frequency. We discuss trends and trade-offs in the optimization of excitation conditions and material choice (such material loss, band structure, and index dispersion), and provide a figure of merit through which the performance of future materials may be evaluated. By illuminating the framework of the nonlinearity, we hope to propel future applications in this growing field.

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Adiabatic frequency shifting in epsilon-near-zero materials –the role of group velocity

2020-01-01

The conversion of a photon’s frequency has long been a key application area of nonlinear optics. It has been discussed how a slow temporal variation of a material’s refractive index can lead to the adiabatic frequency shift (AFS) of a pulse spectrum. Such a rigid spectral change has relevant technological implications, for example, in ultrafast signal processing. Here, we investigate the AFS process in epsilon-near-zero (ENZ) materials and show that the frequency shift can be achieved in a shorter length if operating in the vicinity of Re{

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Enhanced Nonlinear Refractive Index in ε-Near-Zero Materials

2016 New propagation regimes for light arise from the ability to tune the dielectric permittivity to extremely low values. Here, we demonstrate a universal approach based on the low linear permittivity values attained in the ε-near-zero (ENZ) regime for enhancing the nonlinear refractive index, which enables remarkable light-induced changes of the material properties. Experiments performed on Al-doped ZnO (AZO) thin films show a sixfold increase of the Kerr nonlinear refractive index (n2) at the ENZ wavelength, located in the 1300 nm region. This in turn leads to ultrafast light-induced refractive index changes of the order of unity, thus representing a new paradigm for nonlinear optics.

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Al:ZnO as a platform for near-zero-index photonics: enhancing the doping efficiency of atomic layer deposition

2021-08-02

Major technological breakthroughs are often driven by advancements in materials research, and optics is no different. Over the last few years, near-zero-index (NZI) materials have triggered significant interest owing to their exceptional tunability of optical properties and enhanced light-matter interaction, leading to several demonstrations of compact, energy-efficient, and dynamic nanophotonic devices. Many of these devices have relied on transparent conducting oxides (TCOs) as a dynamic layer, as these materials exhibit a near-zero-index at telecommunication wavelengths. Among a wide range of techniques employed for the deposition of TCOs, atomic layer deposition (ALD) offers advantages such as conformality, scalability, and low substrate temperature. However, the ALD process often results in films with poor optical quality, due to low doping efficiencies at high (>1020cm−3) doping levels. In this work, we demonstrate a modified ALD process to deposit TCOs, taking Al:ZnO as an example, which results in an increase in doping efficiency from 13% to 54%. Moving away from surface saturation for the dopant (aluminum) precursor, the modified ALD process results in a more uniform distribution of dopants (Al) throughout the film, yielding highly conductive (2.8×10−4 Ω-cm) AZO films with crossover wavelengths as low as 1320nm and 1370nm on sapphire and silicon substrates, respectively.

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Examining nanophotonics for integrated hybrid systems: a review of plasmonic interconnects and modulators using traditional and alternative materials

2015 The scaling that has governed the continual increase in density, performance, and efficiency of electronic devices is rapidly reaching its inevitable limitations. In order to sustain the trend of ever-increasing bandwidth and performance, new technologies are being considered. Among the many competitors, nanophotonic technologies are especially poised to have an impact on the field of integrated devices. Here, we examine the available technologies, both traditional photonics and plasmonics, with emphasis on the latter. A summary of the previous advances in the field of nanophotonics (interconnects and modulators), along with more recent works investigating novel and CMOS-compatible materials, are presented with a graphical comparison of their performance. We suggest that nanophotonic technologies offer key advantages for future hybrid electrophotonic devices, where the movement toward new material platforms is a precursor to high-performance, industry-ready devices.

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Low loss Plasmon-assisted electro-optic modulator

2018-04-01

For nearly two decades, researchers in the field of plasmonics 1 -which studies the coupling of electromagnetic waves to the motion of free electrons near the surface of a metal 2 -have sought to realize subwavelength optical devices for information technology3-6, sensing7,8, nonlinear optics9,10, optical nanotweezers 11 and biomedical applications 12 . However, the electron motion generates heat through ohmic losses. Although this heat is desirable for some applications such as photo-thermal therapy, it is a disadvantage in plasmonic devices for sensing and information technology 13 and has led to a widespread view that plasmonics is too lossy to be practical. Here we demonstrate that the ohmic losses can be bypassed by using 'resonant switching'. In the proposed approach, light is coupled to the lossy surface plasmon polaritons only in the device's off state (in resonance) in which attenuation is desired, to ensure large extinction ratios between the on and off states and allow subpicosecond switching. In the on state (out of resonance), destructive interference prevents the light from coupling to the lossy plasmonic section of a device. To validate the approach, we fabricated a plasmonic electro-optic ring modulator. The experiments confirm that low on-chip optical losses, operation at over 100 gigahertz, good energy efficiency, low thermal drift and a compact footprint can be combined in a single device. Our result illustrates that plasmonics has the potential to enable fast, compact on-chip sensing and communications technologies.

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Plasmonic Colors in Titanium Nitride for Robust and Covert Security Features

2021-06-01

A mechanically robust metasurface exhibiting plasmonic colors across the visible and the near-IR spectrum is designed, fabricated, and characterized. Thin TiN layers (41 nm in thickness) prepared by plasma-enhanced atomic layer deposition (ALD) are patterned with sub-wavelength apertures (75 nm to 150 nm radii), arranged with hexagonal periodicity. These patterned films exhibit extraordinary transmission in the visible and the near-IR spectrum (550 nm to 1040 nm), which is accessible by conventional Si CCD detectors. The TiN structures are shown to withstand high levels of mechanical stresses, tested by rubbing the films against a lint-free cloth under 14.5 kPa of load for 30 minutes, while structures patterned on gold, a widely used plasmonic material, do not. The subwavelength nature of the plasmonic resonances, coupled with robustness and durability of TiN, makes these structures an attractive choice for use in nanoscale security features for heavily handled objects. Furthermore, ALD of these films enables scalability, which in conjunction with the cost-effectiveness of the process and material (TiN) makes the entire process industry friendly.

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