Jessie Rosenberg

Coherent mixing of mechanical excitations in nano-optomechanical structures

The combination of the large per-photon optical force and small motional mass achievable in nanocavity optomechanical systems results in strong dynamical back-action between mechanical motion and the cavity light field. In this Article, we study the optical control of mechanical motion within two different nanocavity structures, a zipper nanobeam photonic crystal cavity and a double-microdisk whispering-gallery resonator. The strong optical gradient force within these cavities is shown to introduce significant optical rigidity into the structure, with the dressed mechanical states renormalized into optically bright and optically dark modes of motion. With the addition of internal mechanical coupling between mechanical modes, a form of optically controlled mechanical transparency is demonstrated in analogy to electromagnetically induced transparency of three-level atomic media. Based upon these measurements, a proposal for coherently transferring radio-frequency/microwave signals between the optical field and a long-lived dark mechanical state is described.

Mechanical Oscillation and Cooling Actuated by the Optical Gradient Force

In this work, we combine the large per-photon optical gradient force with the sensitive feedback of a high quality factor whispering-gallery microcavity. The cavity geometry, consisting of a pair of silica disks separated by a nanoscale gap, shows extremely strong dynamical backaction, powerful enough to excite coherent oscillations even under heavily damped conditions (mechanical Q approximately 4). In vacuum, the threshold for regenerative mechanical oscillation is lowered to an optical input power of only 270 nW, or roughly 1000 stored cavity photons, and efficient cooling of the mechanical motion is obtained with a temperature compression factor of nearly 14 dB with an input optical power of only 11 microW.

A multispectral and polarization-selective surface-plasmon resonant midinfrared detector

We demonstrate a multispectral polarization sensitive midinfrared dots-in-a-well photodetector utilizing surface-plasmonic resonant elements, with tailorable frequency response and polarization selectivity. The resonant responsivity of the surface-plasmon detector shows an enhancement of up to five times that of an unpatterned control detector. As the plasmonic resonator involves only surface patterning of the top metal contact, this method is independent of light-absorbing material and can easily be integrated with current focal plane array processing for imaging applications.

High-Q double-disk microcavities for cavity optomechanics

We design a double-disk microcavity consisting of a pair of silica microdisks separated by a nanoscale gap region on a silicon chip for cavity optomechanics. We show that this type of photonic structure can provide a per-photon gradient force with a magnitude much larger than for scattering-force-based structures. Moreover, this device provides for nearly independent optimization of optical and mechanical properties. We present the processing details of fabricated devices.

Design of plasmonic photonic crystal resonant cavities for polarization sensitive infrared photodetectors

We design a polarization-sensitive resonator for use in mid-infrared photodetectors, utilizing a photonic crystal cavity and a single or double-metal plasmonic waveguide to achieve enhanced detector efficiency due to superior optical confinement within the active region. As the cavity is highly frequency and polarization-sensitive, this resonator structure could be used in chip-based infrared spectrometers and cameras that can distinguish among different materials and temperatures to a high degree of precision.

Multispectral Quantum Dots-in-a-Well Infrared Detectors Using Plasmon Assisted Cavities

We present the design, fabrication, and characterization, of multi-spectral quantum dots-in-a-well (DWELL) infrared detectors, by the integration of a surface plasmon assisted resonant cavity with the infrared detector. A square lattice and rectangular lattice cavity, formed by modifying the square lattice have been used in this design. By confining the resonant mode of the cavity to detector active region, the detector responsivity and detectivity have been improved by a factor of 5. A spectral tuning of 5.5 to 7.2 ¿m has been observed in the peak response of the detectors, by tuning the lattice constant of the cavity. Simulations indicate the presence of two modes of absorption, which have been experimentally verified. The use of a rectangular lattice predicts highly polarization sensitive modes in x- and y-direction, which are observed in fabricated detectors. A peak detectivity of 3.1 x 109 cm·¿{Hz} /W was measured at 77 K. This design offers a cost-effective and simple method of encoding spectral and polarization information, in infrared focal plane arrays.

Plasmon assisted photonic crystal quantum dot sensors

We report Quantum Dot Infrared Detectors (QDIP) where light coupling to the self assembled quantum dots is achieved through plasmons occurring at the metal-semiconductor interface. The detector structure consists of an asymmetric InAs/InGaAs/GaAs dots-in-a-well (DWELL) structure and a thick layer of GaAs sandwiched between two highly doped n-GaAs contact layers, grown on a semi-insulating GaAs substrate. The aperture of the detector is covered with a thin metallic layer which along with the dielectric layer confines light in the vertical direction. Sub-wavelength two-dimensional periodic patterns etched in the metallic layer covering the aperture of the detector and the active region creates a micro-cavity that concentrate light in the active region leading to intersubband transitions between states in the dot and the ones in the well. The sidewalls of the detector were also covered with metal to ensure that there is no leakage of light into the active region other than through the metal covered aperture. An enhanced spectral response when compared to the normal DWELL detector is obtained despite the absence of any aperture in the detector. The spectral response measurements show that the Long Wave InfraRed (LWIR) region is enhanced when compared to the Mid Wave InfraRed (MWIR) region. This may be due to coupling of light into the active region by plasmons that are excited at the metal-semiconductor interface. The patterned metal-dielectric layers act as an optical resonator thereby enhancing the coupling efficiency of light into the active region at the specified frequency. The concept of plasmon-assisted coupling is in principle technology agnostic and can be easily integrated into present day infrared sensors.

Sensitive phonon detection in a spiderweb optomechanical resonator

We report position-squared coupling six orders of magnitude larger than previously demonstrated, allowing measurement of as few as 652 phonons and presenting a practical route toward probing of single-phonon jumps and characterization of phonon statistics.

Manipulating motion with light: Gradient force optomechanics in double-disk microcavities

Optical forces have been utilized in wide-ranging applications, from optical tweezing to laser cooling, for nearly forty years. Utilizing a double-microdisk nano-optomechanical system, we demonstrate coherent mechanical oscillation, highly efficient self-cooling, broadband wavelength routing, fast optical switching, and sensitive phonon detection in a simple, on-chip silicon-based platform.

Origin of resonant peaks in plasmonic dots-in-a-well infrared detectors

Resonant peaks in plasmonic dots-in-a-well infrared detector is reported. The detectors used here have active layers with InAs quantum dots embedded in InGaAs/GaAs quantum wells. The active region is embedded in heavily n-doped GaAs top and bottom contacts and has a thick Al0.7Ga0.3As layer below the bottom contact as a cladding.