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Shape-Dependent Light Scattering Properties of Subwavelength Silicon Nanoblocks
Ee, Ho-Seok,Kang, Ju-Hyung,Brongersma, Mark L.,Seo, Min-Kyo American Chemical Society 2015 NANO LETTERS Vol.15 No.3
<P>We explore the shape-dependent light scattering properties of silicon (Si) nanoblocks and their physical origin. These high-refractive-index nanostructures are easily fabricated using planar fabrication technologies and support strong, leaky-mode resonances that enable light manipulation beyond the optical diffraction limit. Dark-field microscopy and a numerical modal analysis show that the nanoblocks can be viewed as truncated Si waveguides, and the waveguide dispersion strongly controls the resonant properties. This explains why the lowest-order transverse magnetic (TM<SUB>01</SUB>) mode resonance can be widely tuned over the entire visible wavelength range depending on the nanoblock length, whereas the wavelength-scale TM<SUB>11</SUB> mode resonance does not change greatly. For sufficiently short lengths, the TM<SUB>01</SUB> and TM<SUB>11</SUB> modes can be made to spectrally overlap, and a substantial scattering efficiency, which is defined as the ratio of the scattering cross section to the physical cross section of the nanoblock, of ∼9.95, approaching the theoretical lowest-order single-channel scattering limit, is achievable. Control over the subwavelength-scale leaky-mode resonance allows Si nanoblocks to generate vivid structural color, manipulate forward and backward scattering, and act as excellent photonic artificial atoms for metasurfaces.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-3/nl504442v/production/images/medium/nl-2014-04442v_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl504442v'>ACS Electronic Supporting Info</A></P>
Cavity <tex> $Q$</tex> Measurements of Silica Microspheres with Nanocluster Silicon Active Layer
Sung, Joo-Yeon,Tewary, Anuranjita,Brongersma, Mark L.,Shin, Jung H. IEEE 2006 IEEE journal of selected topics in quantum electro Vol.12 No.6
<P>In this paper, the effect of the nanocluster-silicon (nc-Si) active layer on the cavity Q of silica microspheres is investigated. The silicon-rich silicon oxide (SRSO) (140plusmn10 nm thick) films with excess Si content ranging from 5 to 14 at.% were deposited on the silica microspheres formed by the CO<SUB>2</SUB> laser melting of an optical fiber, and subsequently annealed at temperatures ranging from 650degC to 1100 degC. The cavity Q of the spheres with the active layer was measured at 1.56 mum using a tunable external cavity coupled laser diode and a tapered fiber coupling. We find that the presence of the nc-Si active layer reduces the Q value of the microsphere from ges 2times10<SUP>7</SUP> to (2-5) times10<SUP>5</SUP>. However, we found no correlation between the formation, size, and density of the nc-Si and the cavity Q-factor, indicating that the scattering by the nc-Si does not present the dominant optical loss mechanism in the SRSO film</P>
Sukhdeo, David S,Nam, Donguk,Kang, Ju-Hyung,Brongersma, Mark L,Saraswat, Krishna C Optical Society of America 2015 Optics express Vol.23 No.13
<P>Strain engineering has proven to be vital for germanium-based photonics, in particular light emission. However, applying a large permanent biaxial tensile strain to germanium has been a challenge. We present a simple, CMOS-compatible technique to conveniently induce a large, spatially homogenous strain in circular structures patterned within germanium nanomembranes. Our technique works by concentrating and amplifying a pre-existing small strain into a circular region. Biaxial tensile strains as large as 1.11% are observed by Raman spectroscopy and are further confirmed by photoluminescence measurements, which show enhanced and redshifted light emission from the strained germanium. Our technique allows the amount of biaxial strain to be customized lithographically, allowing the bandgaps of different germanium structures to be independently customized in a single mask process.</P>
Silicon-Nanocrystal-Coated Silica Microsphere Thermooptical Switch
Tewary, Anuranjita,Digonnet, Michel J. F.,Sung, Joo-Yeon,Shin, Jung H.,Brongersma, Mark L. IEEE 2006 IEEE journal on selected topics in quantum electro Vol.12 No.6
<P>We report on a low-switching-energy, all-optical fiber switch that consists of a silica microsphere resonator coated with a silica layer containing silicon nanocrystals. A signal at 1450 nm and a pump at 488 nm are coupled into the microsphere through a tapered fiber. When a pump pulse is launched into the sphere, it is absorbed by the nanocrystal layer, causing the sphere to heat up and change its refractive index. The index change can be exploited to switch the signal by shifting the microsphere resonance. A resonance wavelength shift of 5 pm, sufficient to fully switch the signal, was observed with a pump pulse energy of only 85 nJ. The rise time of the switch was ~25 ms (limited by the pump peak power) and its fall time was ~30 ms (limited by the sphere's thermal time constant). The product of the switching peak power (3.4 mu W) and the device's characteristic dimension (a diameter of 150 mum) is 5.1times10<SUP>-10</SUP> Wm, one of the lowest values reported for an all-optical fiber switch</P>