Highly tunable elastic dielectric metasurface lenses

Dielectric metasurfaces are two‐dimensional structures composed of nano‐scatterers that manipulate the phase and polarization of optical waves with subwavelength spatial resolution, thus enabling ultra‐thin components for free‐space optics. While high performance devices with various functionalities, including some that are difficult to achieve using conventional optical setups have been shown, most demonstrated components have fixed parameters. Here, we demonstrate highly tunable dielectric metasurface devices based on subwavelength thick silicon nano‐posts encapsulated in a thin transparent elastic polymer. As proof of concept, we demonstrate a metasurface microlens operating at 915 nm, with focal distance tuning from 600 μm to 1400 μm (over 952 diopters change in optical power) through radial strain, while maintaining a diffraction limited focus and a focusing efficiency above 50%. The demonstrated tunable metasurface concept is highly versatile for developing ultra‐slim, multi‐functional and tunable optical devices with widespread applications ranging from consumer electronics to medical devices and optical communications.

     

Coupling of nitrogen-vacancy centers to photonic crystal cavities in monocrystalline diamond

The zero-phonon transition rate of a nitrogen-vacancy center is enhanced by a factor of ～70 by coupling to a photonic crystal resonator fabricated in monocrystalline diamond using standard semiconductor fabrication techniques. Photon correlation measurements on the spectrally filtered zero-phonon line show antibunching, a signature that the collected photoluminescence is emitted primarily by a single nitrogen-vacancy center. The linewidth of the coupled nitrogen-vacancy center and the spectral diffusion are characterized using high-resolution photoluminescence and photoluminescence excitation spectroscopy.     

Ultrafast photon-photon interaction in a strongly coupled quantum dot-cavity system

We study dynamics of the interaction between two weak light beams mediated by a strongly coupled quantum dot-photonic crystal cavity system. First, we perform all-optical switching of a weak continuous-wave signal with a pulsed control beam, and then perform switching between two weak pulsed beams (40 ps pulses). Our results show that the quantum dot-nanocavity system enables fast, controllable optical switching at the single-photon level.     

Reflective silicon binary diffraction grating for visible wavelengths

We introduce a device based on subwavelength resonant grating technology. Using a single lithography step we built a reflective binary grating that mimics the functionality of a blazed diffraction grating in a flat geometry. We have also demonstrated that efficient subwavelength resonant devices for visible wavelengths can be built using silicon.