Observation of Acoustically Induced Dressed States of Rare-Earth Ions.

Acoustically induced dressed states of long-lived erbium ions in a crystal are demonstrated. These states are formed by rapid modulation of two-level systems via strain induced by surface acoustic waves whose frequencies exceed the optical linewidth of the ion ensemble. Multiple sidebands and the reduction of their intensities appearing near the surface are evidence of a strong interaction between the acoustic waves and the ions. This development allows for on-chip control of long-lived ions and paves the way to highly coherent hybrid quantum systems with telecom photons, acoustic phonons, and electrons.

Rare-Earth-Mediated Optomechanical System in the Reversed Dissipation Regime.

Strain-mediated interaction between phonons and telecom photons is demonstrated using excited states of erbium ions embedded in a mechanical resonator. Owing to the extremely long-lived nature of rare-earth ions, the dissipation rate of the optical resonance falls below that of the mechanical one. Thus, a "reversed dissipation regime" is achieved in the optical frequency region. We experimentally demonstrate an optomechanical coupling rate g_{0}=2π×21.7 Hz, and numerically reveal that the interaction causes stimulated excitation of erbium ions. Numerical analyses further indicate the possibility of g_{0} exceeding the dissipation rates of erbium and mechanical systems, thereby leading to single-photon strong coupling. This strain-mediated interaction, moreover, involves the spin degree of freedom, and has a potential to be extended to highly coherent opto-electro-mechanical hybrid systems in the reversed dissipation regime.

Epitaxial single-crystal rare-earth oxide in horizontal slot waveguide for silicon-based integrated active photonic devices.

We have epitaxially grown high-quality single-crystal rare-earth oxide thin films, including Gd2O3 and erbium-incorporated (ErGd)2O3, on silicon-on-insulator substrate, and investigated their optical properties when embedded in horizontal slot waveguides. (ErGd)2O3 with an erbium concentration in the mid-1021 cm-3 range shows well-resolved Stark-split photoluminescence emission peaks in the telecommunications band and a photoluminescence lifetime-concentration product as large as 2.67×1018 s·cm-3 at room-temperature. Using these materials, horizontal slot waveguides with strong optical confinement in low-refractive-index rare-earth oxide layers, have been fabricated for silicon-based integrated active photonic devices. Thanks to the strong light-matter interaction, a large waveguide modal absorption of 88 dB/cm related to erbium ions is achieved, leading to a large potential optical gain. Intense emissions from the waveguides are also observed, with a radiation efficiency on the order of 10-4. These results indicate that a combination of epitaxial rare-earth oxide thin films and horizontal slot waveguides provides a promising platform for light amplification and generation on silicon.

Optical coherent transients in 167Er3+ at telecom-band wavelength.

We demonstrate optical coherent transients in a Λ-like hyperfine energy-level system of Er1673+ in yttrium orthosilicate (Y2SiO5) with telecom-band photons at a zero magnetic field. Spectral hole burning was used to study the temperature dependence of the induced spectral antihole. We find that temperatures below 3.0 K suppress population dissipation induced by electron-phonon interactions sufficiently to enable population initialization in the Λ-like system. Further, the pulse area dependence of photoluminescence (PL) from the Λ-like system was measured at 2.2 K. An optical pump power dependence of PL intensity shows Rabi oscillations that contain two full Rabi cycles at the frequency of 2π×810 kHz. A two-pulse photon echo measurement reveals an optical coherence time of 12 µs. To date, this measured optical coherence time is the longest observed for Er3+ in solids at zero magnetic field. These findings will facilitate optical coherent manipulation of Λ-like Er1673+ electronic states as a quantum memories operating at telecom-band wavelengths.

Telecom-band lasing in single InP/InAs heterostructure nanowires at room temperature.

Telecom-band single nanowire lasers made by the bottom-up vapor-liquid-solid approach, which is technologically important in optical fiber communication systems, still remain challenging. Here, we report telecom-band single nanowire lasers operating at room temperature based on multi-quantum-disk InP/InAs heterostructure nanowires. Transmission electron microscopy studies show that highly uniform multi-quantum-disk InP/InAs structure is grown in InP nanowires by self-catalyzed vapor-liquid-solid mode using indium particle catalysts. Optical excitation of individual nanowires yielded lasing in telecom band operating at room temperature. We show the tunability of laser wavelength range in telecom band by modulating the thickness of single InAs quantum disks through quantum confinement along the axial direction. The demonstration of telecom-band single nanowire lasers operating at room temperature is a major step forward in providing practical integrable coherent light sources for optoelectronics and data communication.

Dynamic Control of the Coupling between Dark and Bright Excitons with Vibrational Strain.

We numerically and experimentally investigate strain-induced coupling between dark and bright excitons and its dynamic control using a gallium arsenide (GaAs) micromechanical resonator. Uniaxial strain induced by the mechanical resonance efficiently detunes the exciton energies and modulates the coupling strength via the deformation potential in GaAs. This allows optical access to the long-lived dark states without using any external electromagnetic field. This field-free approach could be expanded to a wide range of solid-state materials, leading to on-chip excitonic memories and circuits based on micromechanical resonators.

Scandium effect on the luminescence of Er-Sc silicates prepared from multi-nanolayer films.

Polycrystalline Er-Sc silicates (Er x Sc2-x Si2O7 and Er x Sc2-x SiO5) were fabricated using multilayer nanostructured films of Er2O3/SiO2/Sc2O3 deposited on SiO2/Si substrates by RF sputtering and thermal annealing at high temperature. The films were characterized by synchrotron radiation grazing incidence X-ray diffraction, cross-sectional transmission electron microscopy, energy-dispersive X-ray spectroscopy, and micro-photoluminescence measurements. The Er-Sc silicate phase Er x Sc2-x Si2O7 is the dominant film, and Er and Sc are homogeneously distributed after thermal treatment because of the excess of oxygen from SiO2 interlayers. The Er concentration of 6.7 × 10(21) atoms/cm(3) was achieved due to the presence of Sc that dilutes the Er concentration and generates concentration quenching. During silicate formation, the erbium diffusion coefficient in the silicate phase is estimated to be 1 × 10(-15) cm(2)/s at 1,250°C. The dominant Er x Sc2 - x Si2O7 layer shows a room-temperature photoluminescence peak at 1,537 nm with the full width at half maximum (FWHM) of 1.6 nm. The peak emission shift compared to that of the Y-Er silicate (where Y and Er have almost the same ionic radii) and the narrow FWHM are due to the small ionic radii of Sc(3+) which enhance the crystal field strength affecting the optical properties of Er(3+) ions located at the well-defined lattice sites of the Sc silicate. The Er-Sc silicate with narrow FWHM opens a promising way to prepare photonic crystal light-emitting devices.