Joshua Hendrickson

Vacuum Rabi Splitting with a Single Quantum Dot in a Photonic Crystal Nanocavity

Cavity quantum electrodynamics (QED) systems allow the study of a variety of fundamental quantum-optics phenomena, such as entanglement, quantum decoherence and the quantum–classical boundary. Such systems also provide test beds for quantum information science. Nearly all strongly coupled cavity QED experiments have used a single atom in a high-quality-factor (high-Q) cavity. Here we report the experimental realization of a strongly coupled system in the solid state: a single quantum dot embedded in the spacer of a nanocavity, showing vacuum-field Rabi splitting exceeding the decoherence linewidths of both the nanocavity and the quantum dot. This requires a small-volume cavity and an atomic-like two-level system. The photonic crystal slab nanocavity—which traps photons when a defect is introduced inside the two-dimensional photonic bandgap by leaving out one or more holes—has both high Q and small modal volume V, as required for strong light–matter interactions. The quantum dot has two discrete energy levels with a transition dipole moment much larger than that of an atom, and it is fixed in the nanocavity during growth.

Scanning a photonic crystal slab nanocavity by condensation of xenon

Allowing xenon or nitrogen gas to condense onto a photonic crystal slab nanocavity maintained at 10–20 K results in shifts of the nanocavity mode wavelength by as much as 5 nm (~=4 meV). This occurs in spite of the fact that the mode defect is achieved by omitting three holes to form the spacer. This technique should be useful in changing the detuning between a single quantum dot transition and the nanocavity mode for cavity quantum electrodynamics experiments, such as mapping out a strong coupling anticrossing curve. Compared with temperature scanning, it has a much larger scan range and avoids phonon broadening.

Wideband perfect light absorber at midwave infrared using multiplexed metal structures

We experimentally demonstrate a wideband near-perfect light absorber in the midwave IR region using a multiplexed plasmonic metal structure. The wideband near-perfect light absorber is made of two different size gold metal squares multiplexed on a thin dielectric spacing layer on top of a thick metal layer in each unit cell. We also fabricate regular nonmultiplexed structure perfect light absorbers. The multiplexed structure IR absorber absorbs more than 98% of the incident light over a much wider spectral band than regular nonmultiplexed structure perfect light absorbers in the midwave IR region.

Multi-Spectral Near Perfect Metamaterial Absorbers Using Spatially Multiplexed Plasmon Resonance Metal Square Structures (Preprint)

Near-perfect IR light absorption at multiple wavelengths has been experimentally demonstrated by using multiplexed metal square plasmonic resonance structures. Optical power absorption over 95% has been observed in dual-band metamaterial absorbers at two separate wavelengths, and optical power absorption over 92.5% has been observed in triple-band metamaterial absorbers at three separate wavelengths. The peak absorption wavelengths are primarily determined by the sizes of the metal squares in the multiplexed structures. Electrical field distributions in the middle of the dielectric spacer layer were calculated at the peak absorption wavelengths. It is found that the strong light absorption corresponds to local quadrupole plasmon resonance modes in the metamaterial structures.

Mid- to long-wavelength infrared plasmonic-photonics using heavily doped n-Ge/Ge and n-GeSn/GeSn heterostructures

Heavily doped n-type Ge and GeSn are investigated as plasmonic conductors for integration with undoped dielectrics of Si, SiGe, Ge, and GeSn in order to create a foundry-based group IV plasmonics technology. N-type Ge1-xSnx with compositions of 0 ≤ x ≤ 0.115 are investigated utilizing effective-mass theory and Drude considerations. The plasma wavelengths, relaxation times, and complex permittivities are determined as functions of the free carrier concentration over the range of 10(10) to 10(21) cm-3. Basic plasmonic properties such as propagation loss and mode height are calculated and example numerical simulations are shown of a dielectric-conductor-dielectric ribbon waveguide structure are shown. Practical operation in the 2 to 20 μm wavelength range is predicted.

Excitonic polaritons in Fibonacci quasicrystals.

The fabrication and characterization of light-emitting one-dimensional photonic quasicrystals based on excitonic resonances is reported. The structures consist of high-quality GaAs/AlGaAs quantum wells grown by molecular-beam epitaxy with wavelength-scale spacings satisfying a Fibonacci sequence. The polaritonic (resonant light-matter coupling) effects and light emission originate from the quantum well excitonic resonances. Measured reflectivity spectra as a function of detuning between emission and Bragg wavelength are in good agreement with excitonic polariton theory. Photoluminescence experiments show that active photonic quasicrystals, unlike photonic crystals, can be good light emitters: While their long-range order results in a stopband similar to that of photonic crystals, the lack of periodicity results in strong emission.

Ultrasensitive silicon photonic-crystal nanobeam electro-optical modulator: Design and simulation

Design and simulation results are presented for an ultralow switching energy, resonator based, silicon-on-insulator (SOI) electro-optical modulator. The nanowire waveguide and Q ~8500 resonator are seamlessly integrated via a high-transmission tapered 1D photonic crystal cavity waveguide structure. A lateral p-n junction of modulation length L(m) ~λ is used to alter the index of refraction and, therefore, shift the resonance wavelength via fast carrier depletion. Differential signaling of the device with ΔV ~0.6 Volts allows for a 6 dB extinction ratio at telecom wavelengths with an energy cost as low as 14 attojoules/bit.

Long-wave infrared tunable thin-film perfect absorber utilizing highly doped silicon-on-sapphire

We show that nearly perfect absorption can be achieved in a simple structure with highly doped silicon on a sapphire (SOS) substrate. An SOS structure with the n-Si film being 600 nm thick and having doping concentration of 2e19 cm(-3) has an absorption peak of 96% in the film at a wavelength of 12.1 μm. More generally, 95% absorption in the n-Si can be achieved and tailored to specific wavelengths in the range of 11.6-15.1 μm utilizing dopings of 1-2.4e19 cm(-3) and film thicknesses of 600-1000 nm. Regions of 90% absorption can be achievable down to 11 μm and up to as much as 22 μm with tailoring of doping and film thickness. It is also shown that choice of substrate with large k/n (imaginary over real part of refractive index) is imperative for high absorption in the thin-film and will play a role in tailoring possibilities. Shown here are results for n-Si, but in general these results also apply to p-Si and the methods may be used to investigate structures with alternative films or substrates. This investigated SOS structure has high potential since desired film thickness and doping investigated here for perfect absorption can be purchased commercially and easily tuned by etching the silicon film.

Metasurface optical antireflection coating

Light reflection at the boundary of two different media is one of the fundamental phenomena in optics, and reduction of reflection is highly desirable in many optical systems. Traditionally, optical antireflection has been accomplished using single- or multiple-layer dielectric films and graded index surface structures in various wavelength ranges. However, these approaches either impose strict requirements on the refractive index matching and film thickness, or involve complicated fabrication processes and non-planar surfaces that are challenging for device integration. Here, we demonstrate an antireflection coating strategy, both experimentally and numerically, by using metasurfaces with designer optical properties in the mid-wave infrared. Our results show that the metasurface antireflection is capable of eliminating reflection and enhancing transmission over a broad spectral band and a wide incidence angle range. The demonstrated antireflection technique has no requirement on the choice of materials and is scalable to other wavelengths.

One dimensional resonant Fibonacci quasicrystals: noncanonical linear and canonical nonlinear effects

A detailed experimental and theoretical study of the linear and nonlinear optical properties of different Fibonacci-spaced multiple-quantum-well structures is presented. Systematic numerical studies are performed for different average spacing and geometrical arrangement of the quantum wells. Measurements of the linear and nonlinear (carrier density dependent) reflectivity are shown to be in good agreement with the computational results. As the pump pulse energy increases, the excitation-induced dephasing broadens the exciton resonances resulting in a disappearance of sharp features and reduction in peak reflectivity.