Quantum confinement in oxide heterostructures: room-temperature intersubband absorption in SrTiO3/LaAlO3 multiple quantum wells

The Si-compatibility of perovskite heterostructures offers the intriguing possibility of producing oxide-based quantum well (QW) optoelectronic devices for use in Si photonics. While the SrTiO3/LaAlO3 (STO/LAO) system has been studied extensively in the hopes of using the interfacial 2-dimensional electron gas in Si-integrated electronics, the potential to exploit its giant 2.4 eV conduction band offset in oxide-based QW optoelectronic devices has so far been largely ignored. Here, we demonstrate room-temperature intersubband absorption in STO/LAO QW heterostructures at energies on the order of hundreds of meV, including at energies approaching the critically important telecom wavelength of 1.55 μm. We demonstrate the ability to control the absorption energy by changing the width of the STO well layers by a single unit cell and present theory showing good agreement with experiment. A detailed structural and chemical analysis of the samples via scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) is presented. This work represents an important proof-of-concept for the use of transition metal oxide QWs in Si-compatible optoelectronic devices

Gradient nonlinear Pancharatnam-Berry metasurfaces

We apply the Pancharatnam-Berry phase approach to plasmonic metasurfaces loaded by highly nonlinear multiquantum-well substrates, establishing a platform to control the nonlinear wave front at will based on giant localized nonlinear effects. We apply this approach to design flat nonlinear metasurfaces for efficient second-harmonic radiation, including beam steering, focusing, and polarization manipulation. Our findings open a new direction for nonlinear optics, in which phase matching issues are relaxed, and an unprecedented level of local wave front control is achieved over thin devices with giant nonlinear responses.close0

Intersubband polaritonic metasurfaces for flat nonlinear optics

Much attention has been drawn in recent years towards the creation of two-dimensional equivalents of traditionally three-dimensional optical elements. The reduction in dimensionality offers advantages such as a smaller spatial footprint, reduced manufacturing and operating complexity, and access to more exotic optical functionalities than can be achieved in a traditional bulk optics approach. Metasurface-based flat optical components, comprised of arrays of subwavelength-spaced scatterers, have emerged as a promising candidate for the realization of this vision, but have been largely constrained to the domain of linear interactions of light with matter. Nonlinear effects are intrinsically weak in bulk materials, and even more so across subwavelength volumes, meaning realization of practical and efficient nonlinear optical metasurfaces has generally been out of reach. In this thesis, a series of metasurface designs are proposed and experimentally verified to exhibit record setting nonlinearities across deeply subwavelength volumes. The metasurfaces are comprised of metallic nanoantennas patterned onto multiple-quantum well structures possessing tailored intersubband electronic resonances. We term the ensemble structure an Intersubband Polaritonic Metasurface (IPM), owing to the nature of the coupling of the electromagnetic antenna mode with the electronic intersubband transition. Suitable design of the antenna geometry allows one to access and enhance the giant intrinsic nonlinearity of intersubband transitions, which are subject to polarization-selection rules that typically inhibit their operation configuration. Further, due to their subwavelength thickness, IPMs are not constrained to the typical phase-matching considerations of bulk nonlinear optics. In the first part of this study, we investigate IPMs for efficient second-harmonic generation. A novel architecture consisting of etched nanoantenna volumes is proposed and experimentally demonstrated to exhibit a record setting second-order nonlinearity in the mid-infrared spectral range. Using this design, we experimentally demonstrate a means to control the phase of the generated nonlinear signal via the Pancharatnam-Berry geometric phase approach. We then present and demonstrate a simplified fabrication procedure for the creation of efficient IPMs, forgoing the rather cumbersome wafer-bonding and substrate removal process inherent to earlier designs. Finally, we propose and verify a metasurface design exhibiting an ultrafast third-order nonlinearityElectrical and Computer Engineerin

Infrared Spectroscopy via Selective Thermal Emission of Two Layer Perfect Absorber

Strong absorption (and corresponding emission) from a two-layer system consisting of heavily doped silicon and a high-index germanium dielectric layer is studied. Absorption resonances in the mid-infrared via electrical resistive heating have also been demonstrated to be polarization and angle dependent. Such structures have the potential for applications in thermal signature mimicry, thermal cloaking, and frequency selective infrared sources. The simplicity of fabrication (requiring no photolithographic process) allows for inexpensive and rapid deployment of this engineered structure. In this work, a selective electrical pulsing system is presented and tested to resistively heat a group of germanium-on-silicon samples at a determined pulse frequency. Such a system can conceivably be used to create a cheap infrared spectral imaging system when emissions in the time-domain are resolved approximately.unpublishednot peer reviewedU of I OnlyUndergraduate senior thesis not recommended for open acces

Nonlinear optics with quantum engineered intersubband metasurfaces

We report highly-nonlinear metasurfaces based on combining electromagnetically-engineered plasmonic nanoresonators with quantum-engineered intersubband nonlinearities. Experimentally, effective nonlinear susceptibility over 480 nm/V was measured for second-harmonic generation at normal incidence

Nonlinear optics with quantum-engineered intersubband metamaterials

Intersubband transitions in n-doped semiconductor heterostructures provide the possibility to quantum engineer one of the largest known nonlinear optical responses in condensed matter systems, limited however to electric field polarized normal to the semiconductor layers. Here we show that by coupling of electromagnetic modes in plasmonic metasurfaces with quantum-engineered intersubband transitions in semiconductor heterostructures one can create ultra-thin highlynonlinear metasurfaces for normal light incidence. Structures discussed here represent a novel kind of hybrid metalsemiconductor metamaterials in which exotic optical properties are produced by coupling electromagneticallyengineered modes in dielectric and plasmonic nanostructures with quantum-engineered intersubband transitions in semiconductor heterostructures. Record values of effective optical nonlinearities of over 400 nm/V are experimentally measured for metasurfaces optimized for efficient second harmonic generation at 9.7 ??m pump wavelength under normal incidence

Difference-Frequency Generation in Polaritonic Intersubband Nonlinear Metasurfaces

A nonlinear intersubband polaritonic metasurface designed for difference-frequency generation that provides a practical level of nonlinear response under continuous wave illumination is reported. An effective nonlinear susceptibility of up to 340 nm V-1 is measured experimentally. Approximately 0.3% of = 5.4 mu m photons are downconverted to lambda = 12.9 mu m photons at the focal spot in the experiment. This work indicates that the ultrathin metasurface devices may provide a versatile nonlinear element for frequency down- and upconversion in a relatively broad spectral range and without phase-matching constrains of traditional bulk nonlinear crystals

Giant nonlinear response of polaritonic metasurfaces coupled to intersubband transitions

We report highly-nonlinear metasurfaces based on combining electromagnetically-engineered plasmonic nanoresonators with quantum-engineered intersubband nonlinearities. Experimentally, effective nonlinear susceptibility over 480 nm/V was measured for second-harmonic generation at normal incidence