Publications

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

We theoretically analyze the second harmonic generation capacity of two-dimensional periodic metamaterials comprising sub-wavelength resonators strongly coupled to intersubband transitions in quantum wells (QWs) at mid-infrared frequencies. The metamaterial is designed to support a fundamental resonance at ∼30THz and an orthogonally polarized resonance at the second harmonic frequency (∼60THz), while the asymmetric quantum well structure is designed to provide a large second order susceptibility. Upon continuous wave illumination at the fundamental frequency we observe second harmonic signals in both the forward and backward directions, with the forward efficiency being larger. We calculate the overall second harmonic conversion efficiency of the forward wave to be ∼1.3×10-2 W/W2 - a remarkably large value, given the deep sub-wavelength dimensions of the QW structure (about 1/15th of the free space wavelength of 10μm). The results shown in this Letter provide a strategy for designing easily fabricated sources across the entire infrared spectrum through proper choice of QW and resonator designs. © 2014 AIP Publishing LLC.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Achieving high spatial resolutions for imaging with terahertz (THz) waves requires near-field probes, such as a sub-wavelength aperture probe. Bethe's theory of transmission through a sub-wavelength aperture of size a predicts that the transmitted electric field scales as Eαa3. This strong dependence limits the size of apertures that can be employed and hence the spatial resolution. This dependence however changes for the evanescent field components in very close proximity (∼1μm for THz waves) to the aperture, as shown by electromagnetic simulations. To exploit this effect in a THz near-field probe, we developed a photoconductive THz near-field detector structure, which incorporates a thinned photo-conductive detector region and a distributed Bragg reflector between the detector and the aperture plane. Near-field probes are manufactured with different aperture sizes to investigate transmission of THz pulses through apertures as small as 3μm. The experimental results confirm that the transmitted field amplitude, and therefore the sensitivity, increases by about one order of magnitude for the new probes. A 3μm aperture probe with a spatial resolution of λ/100 at 1THz is demonstrated.. © 2014 SPIE.

The reflection of an optical wave from metal, arising from strong interactions between the optical electric field and the free carriers of the metal, is accompanied by a phase reversal of the reflected electric field. A far less common route to achieving high reflectivity exploits strong interactions between the material and the optical magnetic field to produce a “magnetic mirror” that does not reverse the phase of the reflected electric field. At optical frequencies, the magnetic properties required for strong interaction can be achieved only by using artificially tailored materials. Here, we experimentally demonstrate, for the first time to the best of our knowledge, the magnetic mirror behavior of a low-loss all-dielectric metasurface at infrared optical frequencies through direct measurements of the phase and amplitude of the reflected optical wave. The enhanced absorption and emission of transverse-electric dipoles placed close to magnetic mirrors can lead to exciting new advances in sensors, photodetectors, and light sources.

We demonstrate that THz pulses transmitted through small apertures (~λ/100) exhibit strong evanescent components within 1μm of the aperture. Using this effect, we developed subwavelength aperture THz near-field probes that provide 3μm resolution. © 2014 OSA.

Abstract not provided.

Abstract not provided.

Abstract not provided.

We have demonstrated single-mode lasing in a single gallium nitride nanowire using distributed feedback by external coupling to a dielectric grating. By adjusting the nanowire grating alignment we achieved a mode suppression ratio of 17dB.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

We present an actively tunable mid-infrared metamaterial operating in the strong lightmatter coupling regime. We can tune the upper polariton branch continuously over 8% of the center frequency by applying 5 V. © 2014 OSA.

Abstract not provided.

We present the design, fabrication, and realization of an electrically tunable metamaterial operating in the mid-infrared spectral range. Our devices combine intersubband transitions in semiconductor quantum-wells with planar metamaterials and operate in the strong light-matter coupling regime. The resonance frequency of the intersubband transition can be controlled by an external bias relative to the fixed metamaterial resonance. This allows us to switch dynamically from an uncoupled to a strongly coupled system and thereby to shift the eigenfrequency of the upper polariton branch by 2.5 THz (corresponding to 8% of the center frequency or one full linewidth) with a bias of 5 V. © 2013 AIP Publishing LLC.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

We demonstrate a new type of electrically tunable strong coupling between a planar metamaterial layer and an ultra-thin epsilon-near-zero layer made of a doped semiconductor. This can find novel applications in chip-scale infrared optoelectronic devices. © OSA 2013.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.