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7 Nov 2011

Volume 99, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 193101 (2011); http://dx.doi.org/10.1063/1.3657777 (3 pages)

Sungwook Chung, Jonathan R. Felts, Debin Wang, William P. King, and James J. De Yoreo
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Fast-response signal upconversion by the use of a “time-space conversion” method

Mitsunori Saito, Shingo Nakamura, and Teppei Kita

Appl. Phys. Lett. 99, 191101 (2011); http://dx.doi.org/10.1063/1.3660262 (3 pages)

Online Publication Date: 7 November 2011

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Lanthanide-doped phosphors achieve signal wavelength conversion between visible and infrared communication systems. A long lifetime of their excited states is advantageous for inducing two-photon absorption that realizes upconversion. The long lifetime, however, restricts the conversion rate to ∼500 bit/s because of the afterglow. This contradiction was solved by embedding a phosphor (YbEr:Gd2O2S) in a rotating disk. When an infrared (940 nm) pulse train of 1 Mbit/s (time domain) was focused on the disk, a fluorescent dot array (space domain) was created and moved with the disk rotation. Consequently, a visible (∼550 nm) pulse train was detected on the dot trajectory.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Optical fiber tips functionalized with semiconductor photonic crystal cavities

Gary Shambat, J Provine, Kelley Rivoire, Tomas Sarmiento, James Harris, and Jelena Vučković

Appl. Phys. Lett. 99, 191102 (2011); http://dx.doi.org/10.1063/1.3660278 (3 pages) | Cited 5 times

Online Publication Date: 7 November 2011

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We demonstrate a simple and rapid epoxy-based method for transferring photonic crystal (PC) cavities to the facets of optical fibers. Passive Si cavities were measured via fiber taper coupling as well as direct transmission from the fiber facet. Active quantum dot containing GaAs cavities showed photoluminescence that was collected both in free space and back through the original fiber. Cavities maintain a high quality factor (2000-4000) in both material systems. This design architecture provides a practical mechanically stable platform for the integration of photonic crystal cavities with macroscale optics and opens the door for innovative research on fiber-coupled cavity devices.
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42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design
42.82.Bq Design and performance testing of integrated-optical systems
42.81.Wg Other fiber-optical devices

Biomimetic broadband antireflection gratings on solar-grade multicrystalline silicon wafers

Blayne M. Phillips, Peng Jiang, and Bin Jiang

Appl. Phys. Lett. 99, 191103 (2011); http://dx.doi.org/10.1063/1.3660263 (3 pages) | Cited 4 times

Online Publication Date: 9 November 2011

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We report a simple and scalable bottom-up technique for fabricating broadband antireflection gratings on solar-grade multicrystalline silicon (mc-Si) wafers. A Langmuir-Blodgett process is developed to assemble close-packed silica microspheres on rough mc-Si substrates. Subwavelength moth-eye pillars can then be patterned on mc-Si by using the silica microspheres as structural template. Hemispherical reflectance measurements show that the resulting mc-Si gratings exhibit near zero reflection for a wide range of wavelengths. Both experimental results and theoretical prediction using a rigorous coupled-wave analysis model show that close-packed moth-eye arrays exhibit better antireflection performance than non-close-packed arrays due to a smoother refractive index gradient.
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88.40.jj Silicon solar cells
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Ultra-broadband heterogeneous quantum cascade laser emitting from 2.2 to 3.2 THz

Dana Turčinková, Giacomo Scalari, Fabrizio Castellano, Maria I. Amanti, Mattias Beck, and Jérôme Faist

Appl. Phys. Lett. 99, 191104 (2011); http://dx.doi.org/10.1063/1.3658874 (3 pages) | Cited 9 times

Online Publication Date: 9 November 2011

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We present a heterogeneous terahertz quantum cascade laser that emits continuously between 2.2 and 3.2 THz, covering an emission range of over 40% around the central frequency. Devices were realized by stacking different active region designs into a double-metal waveguide. They operate up to 125 K with 15 mW peak power at 10 K in pulsed mode. Smaller devices show broadband emission also in continuous wave. Time-resolved measurements of the emission spectra were realized, confirming the broadband emission within a 5 ns time window.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultra-high four wave mixing efficiency in slot waveguides with silicon nanocrystals

A. Trita, C. Lacava, P. Minzioni, J.-P. Colonna, P. Gautier, J.-M. Fedeli, and I. Cristiani

Appl. Phys. Lett. 99, 191105 (2011); http://dx.doi.org/10.1063/1.3659694 (3 pages) | Cited 1 time

Online Publication Date: 9 November 2011

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We report on wavelength conversion through four-wave-mixing in silicon slot-waveguides with embedded silicon nanocrystals. The combination of strong optical confinement and Si:nc nonlinearity provides a huge waveguide nonlinear coefficient γ = 1100 W−1m−1. Moreover, the improvement in the fabrication procedure allowed a loss reduction with respect to previous reported structures, enabling the achievement of an extreme value for the conversion efficiency which represents the best result ever reported in the scientific literature.
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42.79.Gn Optical waveguides and couplers
61.46.-w Structure of nanoscale materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Wavelength-dependent frustrated internal reflection via photonic interface states

G. H. Cross and S. Brand

Appl. Phys. Lett. 99, 191106 (2011); http://dx.doi.org/10.1063/1.3660266 (3 pages)

Online Publication Date: 10 November 2011

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Conventional frustrated internal reflection in which light is able to tunnel across a small air gap between two prisms is a well known phenomenon. In this work, an experimental proof-of-concept demonstration of a polarization and highly wavelength selective version of a similar effect via photonic interface states is given. The photonic interface states are designed to exist within the photonic band gap of Bragg reflectors on the surfaces of the two prisms.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.79.Bh Lenses, prisms and mirrors
42.70.Qs Photonic bandgap materials

Tailoring the Faraday effect by birefringence of two dimensional plasmonic nanorod array

G. X. Du, S. Saito, and M. Takahashi

Appl. Phys. Lett. 99, 191107 (2011); http://dx.doi.org/10.1063/1.3660318 (3 pages) | Cited 2 times

Online Publication Date: 10 November 2011

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The ability to rotate the polarization of light propagating through a material by applying a magnetic field was discovered by Faraday. It is critically important for applications involving light modulation and sensors. Shaped plasmonic crystals function as miniature polarizers. This study investigates a gold nanorod array that can be used to significantly vary the Faraday effect originating from a dielectric material. The dependence of the Faraday effect on the polarizer angle exhibited well-defined characteristics. The birefringence of the nanorod array was characterized using a simplified setup for optical polarization tomography. The enhanced Faraday effect due to the plasmonic nanorods is promising for applications involving plasmonic circuits and refractometry.
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78.20.Ls Magneto-optical effects
78.67.Qa Nanorods
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
61.46.-w Structure of nanoscale materials

Adaptive beam tracking and steering via electrowetting-controlled liquid prism

Jiangtao Cheng and Chung-Lung Chen

Appl. Phys. Lett. 99, 191108 (2011); http://dx.doi.org/10.1063/1.3660578 (3 pages) | Cited 3 times

Online Publication Date: 10 November 2011

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We report an electrowetting-controlled optofluidic system for adaptive beam tracking and agile steering. With two immiscible fluids in a transparent cell, we can actively control the contact angle along the fluid-fluid-solid tri-junction line and hence the orientation of the fluid-fluid interface via electrowetting. The naturally formed meniscus between the two liquids can function as an optical prism. We have fabricated a liquid prism module with an aperture size of 10 mm × 10mm. With 1 wt. % KCl and 1 wt. % Sodium Dodecyl Sulfate added into deionized water, the orientation of the water-silicone oil interface has been modulated between −26° and 26° that can deflect and steer beam within the incidence angle of 0°–15°. The wide-range beam tracking and steering enables the liquid prism work as an electrowetting solar cell.
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88.40.H- Solar cells (photovoltaics)
68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena
42.79.Bh Lenses, prisms and mirrors

Enhanced photorefractive effect in liquid crystal structures co-doped with semiconductor quantum dots and metallic nanoparticles

A. Anczykowska, S. Bartkiewicz, M. Nyk, and J. Myśliwiec

Appl. Phys. Lett. 99, 191109 (2011); http://dx.doi.org/10.1063/1.3659485 (3 pages) | Cited 3 times

Online Publication Date: 10 November 2011

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In this paper, we present strong enhancement of optical properties of hybrid liquid crystal structures functionalized with metallic and semiconductor nanoparticles. Several experiments done in two wave mixing experimental set-up have reported that diffraction efficiency can be improved by up to 14 times by introducing nanoparticles of cadmium selenide or gold into the photoconducting polymer adjacent to the liquid crystal layer. Our research may open up a possible route for the development of faster and more efficient holographic materials which can be used in dynamic data processing systems.
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78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
78.20.Mg Photorefractive effects
42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.30.Vx Polymer liquid crystals

Confinement enhancing barriers for high performance quantum dots-in-a-well infrared detectors

A. V. Barve, S. Sengupta, J. O. Kim, Y. D. Sharma, S. Adhikary, T. J. Rotter, S. J. Lee, Y. H. Kim, and S. Krishna

Appl. Phys. Lett. 99, 191110 (2011); http://dx.doi.org/10.1063/1.3660317 (3 pages) | Cited 5 times

Online Publication Date: 11 November 2011

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We demonstrate the use of thin AlGaAs barrier layers in the quantum dots in a well heterostructure to enhance the quantum confinement of carriers in the excited energy level, while maintaining high escape probability. This is achieved by controlling the excited state energy between the confinement enhancing (CE) barriers and the continuum level. Responsivity of ∼0.1 A/W, detectivity of 6.5 × 1010 cmHz1/2 W−1 (77 K, 0.6 V, 7.5 µm, f/2), and a factor of 10 improvement over a control sample without the CE barriers have been measured. The effect of changing the quantum well thickness and quantum dot size is also reported.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Photodiode with nanocrystalline Si/amorphous Si absorber bilayer

Y. Vygranenko, A. Sazonov, M. Fernandes, and M. Vieira

Appl. Phys. Lett. 99, 191111 (2011); http://dx.doi.org/10.1063/1.3660725 (3 pages)

Online Publication Date: 11 November 2011

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This letter reports a near-ultraviolet/visible/near-infrared n+-n-i-δi-p photodiode with an absorber comprising a nanocrystalline silicon n layer and a hydrogenated amorphous silicon i layer. Device modeling reveals that the dominant source of reverse dark current is deep defect states in the n layer, and its magnitude is controlled by the i layer thickness. The photodiode with the 900/400 nm thick n-i layers exhibits a reverse dark current density of 3nA/cm2 at −1 V. Donor concentration and diffusion length of holes in the n layer are estimated from the capacitance-voltage characteristics and from the bias dependence of long-wavelength response, respectively.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling
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