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22 Oct 2007

Volume 91, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 173113 (2007); http://dx.doi.org/10.1063/1.2801551 (3 pages)

Nanfang Yu, Ertugrul Cubukcu, Laurent Diehl, Mikhail A. Belkin, Kenneth B. Crozier, Federico Capasso, David Bour, Scott Corzine, and Gloria Höfler
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Controlling enhanced transmission through metallic gratings with subwavelength slits by anisotropic waveguide resonance

King-Yan Fong and P. M. Hui

Appl. Phys. Lett. 91, 171101 (2007); http://dx.doi.org/10.1063/1.2800802 (3 pages) | Cited 3 times

Online Publication Date: 22 October 2007

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We propose an analytically tractable structure for controlling enhanced transmission through a metallic grating with subwavelength slits by filling the slits with an anisotropic material such as a liquid crystal. As the director rotates, the Fabry-Pérot condition is modified and the transmission peaks shift. Analytical results of a single-mode theory for the propagation constant, transmission efficiency, and the tunable range of peak wavelengths are given, taking the finite conductivity of metal into account. Analytical results are in good agreement with those calculated by the rigorous coupled-wave analysis, indicating that waveguide resonance plays a dominant role and the results are scalable.
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42.25.Bs Wave propagation, transmission and absorption
42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings
42.70.Df Liquid crystals

Experimental transfer of torque induced by localized polarization of radially polarized vector beams to anisotropic microparticles

B. P. S. Ahluwalia, X.-C. Yuan, K. J. Moh, and J. Bu

Appl. Phys. Lett. 91, 171102 (2007); http://dx.doi.org/10.1063/1.2795334 (3 pages) | Cited 8 times

Online Publication Date: 23 October 2007

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Polarization-induced torque of a radially polarized beam is investigated on anisotropic micro-particles. Radially polarized beams possess full cylindrical symmetry; therefore, any line drawn from the beam axis to the circumference contains identical polarization vectors, acting locally as linearly polarized. It is experimentally observed that anisotropic microparticles experience an aligning torque by the localized segment of the radially polarized beam, setting it to rotate around the beam axis. The rotation of the particle thus enables the mapping of the localized electric vector distribution of radially polarized beams.
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42.25.Ja Polarization
42.81.Gs Birefringence, polarization

Surface plasmon coupling effect in an InGaN/GaN single-quantum-well light-emitting diode

Dong-Ming Yeh, Chi-Feng Huang, Cheng-Yen Chen, Yen-Cheng Lu, and C. C. Yang

Appl. Phys. Lett. 91, 171103 (2007); http://dx.doi.org/10.1063/1.2802067 (3 pages) | Cited 40 times

Online Publication Date: 23 October 2007

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The authors demonstrate the coupling effects between the quantum well (QW) and surface plasmon (SP) generated nearby on the p-type side in an InGaN/GaN single-QW light-emitting diode (LED). The QW-SP coupling leads to the enhancement of the electroluminescence (EL) intensity in the LED sample designed for QW-SP coupling and reduced SP energy leakage, when compared to a LED sample of weak QW-SP coupling or significant SP energy loss. In the LED samples of significant QW-SP coupling, the blueshifts of the photoluminescence and EL emission spectra are observed, indicating one of the important features of such a coupling process. The device performance can be improved by using the n-type side for SP generation such that the device resistance can be reduced and the QW-SP coupling effect can be enhanced (by further decreasing the distance between the QW and metal) because of the higher carrier concentration in the n-type layer.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling

Light localization at randomly textured surfaces for solar-cell applications

Carsten Rockstuhl, Falk Lederer, Karsten Bittkau, and Reinhard Carius

Appl. Phys. Lett. 91, 171104 (2007); http://dx.doi.org/10.1063/1.2800374 (3 pages) | Cited 35 times

Online Publication Date: 23 October 2007

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By using a rigorous diffraction theory, the localization of light near textured zinc oxide (ZnO) surfaces is theoretically investigated and compared with experimental data obtained from scanning-near-field-optical microscopy. Although random by nature, these surfaces show well-defined geometrical features, which cause the formation of localized light patterns near the surface. Particularly, photon jets are observed to emerge from conical surface structures. Because these structures are of primary importance for applications in photovoltaics, we analyze the “real” surface topography of textured ZnO used in silicon solar cells. With this work, valuable insight is provided into the mechanism of light coupling through randomly textured interfaces.
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78.68.+m Optical properties of surfaces
84.60.Jt Photoelectric conversion

Phase lenses and mirrors created by laser micronanofabrication via two-photon photopolymerization

Qi-Dai Chen, Dong Wu, Li-Gang Niu, Juan Wang, Xiao-Feng Lin, Hong Xia, and Hong-Bo Sun

Appl. Phys. Lett. 91, 171105 (2007); http://dx.doi.org/10.1063/1.2798505 (3 pages) | Cited 20 times

Online Publication Date: 23 October 2007

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The phase lens, also called kinoform, a promising focusing component in an integrated micro-optical system, was produced by femtosecond laser fabrication via two-photon photopolymerization. Kinoforms consisting of two-, four-, eight-level subzones with level thicknesses of 475, 238, and 119 nm demonstrate diffraction efficiencies of 30%, 54%, and 68%, respectively, which are comparable with the theoretical limit and with those from the commercial phase lenses. In addition, a reflective diffractive micromirror was proposed and realized with the aid of electroless plating. These works show the promising prospect of femtosecond laser fabrication in manufacturing optical micronanodevices and their integrated system with optical quality.
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42.82.Gw Other integrated-optical elements and systems
42.79.Bh Lenses, prisms and mirrors
42.60.By Design of specific laser systems
42.70.Jk Polymers and organics
42.40.Jv Computer-generated holograms

Propagation of laser filaments through an extended turbulent region

R. Salamé, N. Lascoux, E. Salmon, R. Ackermann, J. Kasparian, and J.-P. Wolf

Appl. Phys. Lett. 91, 171106 (2007); http://dx.doi.org/10.1063/1.2799163 (3 pages) | Cited 14 times

Online Publication Date: 23 October 2007

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We show that laser filamentation can be initiated and propagate through strong extended turbulence well above the typical atmospheric values. We suggest that the effect of turbulence on filamentation is characterized by the product of the structure parameter for the refractive index Cn2 and the length L of the turbulence region. Half of the filaments are transmitted for Cn2L ⩽ 4.4×10−10 m1/3. Moreover, the surviving filaments keep their key spectral properties including correlations inside the white-light continuum.
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42.68.Ay Propagation, transmission, attenuation, and radiative transfer
42.68.Bz Atmospheric turbulence effects
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.68.Ca Spectral absorption by atmospheric gases

Study of one-dimensional Bragg structures with localized defect

I. V. Konoplev, P. MacInnes, A. W. Cross, A. D. R. Phelps, and K. Ronald

Appl. Phys. Lett. 91, 171107 (2007); http://dx.doi.org/10.1063/1.2799179 (3 pages) | Cited 5 times

Online Publication Date: 23 October 2007

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The results of studies of one-dimensional Bragg structures (one-dimensional periodic lattice) with localized defects are presented. The defects considered are localized, step changes (shifts) of the lattice phase (corrugation). The influence of the defects on the periodic lattice band-gap parameters has been analyzed. The presence of the defect resulted in the appearance of a pass band, associated with the defect eigenmode, inside the lattice band gap and it was demonstrated that the position of the pass band depended strongly on the parameters of the defect as well as the field structure. The experimental and theoretical results obtained are compared and discussed.
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61.72.-y Defects and impurities in crystals; microstructure
71.20.-b Electron density of states and band structure of crystalline solids

Organic mixed-order photonic crystal lasers with ultrasmall footprint

Kristian Baumann, Thilo Stöferle, Nikolaj Moll, Rainer F. Mahrt, Thorsten Wahlbrink, Jens Bolten, Thomas Mollenhauer, Christian Moormann, and Ulli Scherf

Appl. Phys. Lett. 91, 171108 (2007); http://dx.doi.org/10.1063/1.2801706 (3 pages) | Cited 9 times

Online Publication Date: 24 October 2007

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The lasing properties of an optimized two-dimensional photonic crystal structure with an organic gain material are investigated. The feedback structure which is fabricated in a thin film of Ta2O5 increases both the index contrast from the gain material as well as the optical confinement. By combining first-order and second-order photonic crystal structures, losses occuring at the edge of the second order structure are dramatically reduced leading to a lower laser threshold and/or to a much smaller footprint of the laser.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Hj Laser materials
42.70.Qs Photonic bandgap materials
42.86.+b Optical workshop techniques
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Wc Optical coatings

Transmitting light efficiently on photonic crystal surface waveguide bend

E. H. Khoo, T. H. Cheng, A. Q. Liu, J. Li, and D. Pinjala

Appl. Phys. Lett. 91, 171109 (2007); http://dx.doi.org/10.1063/1.2793175 (3 pages) | Cited 5 times

Online Publication Date: 24 October 2007

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In this letter, the transmission efficiency around waveguide bend on the surface of photonic crystal is investigated. Light is confined to the photonic crystal-air interface by means of surface modes. The transmission efficiency around surface waveguide bend is shown to be very poor. This is due to the phase mismatch of the wave vectors between different sections of the surface waveguide bend. To reduce the phase mismatch between the different waveguide sections, the cell properties at the bend section are modified. As a result, high transmission efficiency of more than 93% around the modified surface waveguide bend structure is achieved.
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84.40.Az Waveguides, transmission lines, striplines
42.70.Qs Photonic bandgap materials

Temperature dependence of polarized electroluminescence from nonpolar m-plane InGaN-based light emitting diodes

Satoshi Nakagawa, Hiroki Tsujimura, Kuniyoshi Okamoto, Masashi Kubota, and Hiroaki Ohta

Appl. Phys. Lett. 91, 171110 (2007); http://dx.doi.org/10.1063/1.2800817 (3 pages) | Cited 24 times

Online Publication Date: 24 October 2007

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An accurate method of estimating polarized light emission was presented for nonpolar m-plane InGaN-based blue light emitting diodes, where the unpolarized component caused by unintentional light scattering was eliminated as noise. The polarization ratios of electroluminescence (EL) at 300 and 100 K were 0.85 and 0.98, respectively. The energy difference between the highest and the second highest valence bands was estimated to be 129 meV from the temperature dependence of the spectrally integrated EL intensities under the assumption of Fermi statistics. This value agreed with the one ( = 118 meV) obtained directly from the difference of the EL peak energies between two polarized components, the electric fields perpendicular and parallel to the c axis.
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85.60.Jb Light-emitting devices
42.25.Fx Diffraction and scattering

Pneumatically actuated adaptive lenses with millisecond response time

Kyle Campbell, Yeshaiahu Fainman, and Alex Groisman

Appl. Phys. Lett. 91, 171111 (2007); http://dx.doi.org/10.1063/1.2801983 (3 pages) | Cited 7 times

Online Publication Date: 25 October 2007

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We describe the design and operation of two pneumatically actuated adaptive lenses with refractive power adjustable by >4 diopters. The refractive element in the lenses is a transparent flexible membrane. When vacuum is applied, the membrane is deformed and becomes a diverging meniscus lens. The two lenses have membranes with 18 and 12 mm diameters and 5 and 2 ms transition times after sudden changes in pressure. Both lenses can be driven at 500 Hz with 4 diopter variation in the refractive power. The adaptive lenses can be used for longitudinal scanning in three-dimensional imaging and for fast focusing.
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42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design
42.25.Gy Edge and boundary effects; reflection and refraction

A photon detector with very high gain at low bias and at room temperature

Omer Gokalp Memis, Alex Katsnelson, Soon-Cheol Kong, Hooman Mohseni, Minjun Yan, Shuang Zhang, Tim Hossain, Niu Jin, and Ilesanmi Adesida

Appl. Phys. Lett. 91, 171112 (2007); http://dx.doi.org/10.1063/1.2802043 (3 pages) | Cited 5 times

Online Publication Date: 25 October 2007

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We report on a photon detector aimed at low light detection, which is based on the combination of small sensing volumes and large absorbing regions. Fabricated devices show stable gain values in the range of 1000–10 000 at bias voltages of ∼ 1 V at 1.55 μm at room temperature. Submicron devices show dark current less than 90 nA and unity gain dark current density values less than 900 nA/cm2. The noise equivalent power (NEP) is measured to be 4 fW/Hz0.5 at room temperature without any gating, which is similar to NEP of current InGaAs/InP avalanche photodetectors in gated operation.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Stable dual-wavelength operation of InGaAs diode lasers with volume Bragg gratings

S. A. Zolotovskaya, N. Daghestani, G. B. Venus, L. B. Glebov, V. I. Smirnov, and E. U. Rafailov

Appl. Phys. Lett. 91, 171113 (2007); http://dx.doi.org/10.1063/1.2802082 (3 pages) | Cited 6 times

Online Publication Date: 25 October 2007

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Stable dual-wavelength operation of InGaAs diode lasers coupled with volume Bragg gratings has been demonstrated for the continuous wave and gain-switching regimes. Spectral narrowing down to 0.33 nm has been realized with maximum output power of up to 1.85 W from a broad area stripe laser diode in a single-grating external cavity configuration. Spectral separation from 0.5 (0.16 THz) to 6.5 nm (2.05 THz) has been obtained and an output power of up to 1.75 W was achieved in dual-wavelength operation.
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42.55.Px Semiconductor lasers; laser diodes

Increase of light extraction from GaN based light emitting diodes incorporating patterned structure by colloidal lithography

Tae Sun Kim, Sang-Mook Kim, Yun Hee Jang, and Gun Young Jung

Appl. Phys. Lett. 91, 171114 (2007); http://dx.doi.org/10.1063/1.2802557 (3 pages) | Cited 27 times

Online Publication Date: 25 October 2007

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The light extraction efficiency of light emitting diodes (LEDs) was enhanced by incorporating nanoscale patterns inside the LED structure. A hole patterned p-GaN layer and a pillar patterned indium-tin-oxide (ITO) contact layer were fabricated by using colloidal lithography with size-tunable polystyrene spheres. It was found that the light output power (at 20 mA) of the LEDs with the hole patterned p-GaN layer and the pillar patterned ITO contact layer were enhanced by 21% and 10%, respectively, compared with the conventional LED due to the increase of the extraction probability of the internally reflected photons through the patterns.
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85.60.Jb Light-emitting devices
85.60.Pg Display systems
81.16.Nd Micro- and nanolithography

Enhanced 1.53 μm photoluminescence from Er-doped AlGaAs wet thermal native oxides by postoxidation implantation

M. Huang and D. C. Hall

Appl. Phys. Lett. 91, 171115 (2007); http://dx.doi.org/10.1063/1.2802560 (3 pages) | Cited 1 time

Online Publication Date: 25 October 2007

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A significant enhancement in the 300 K, cw photoluminescence (PL) from Er-doped Al0.3Ga0.7As native oxide films is achieved by incorporating the Er after (relative to before) wet thermal oxidation of the AlGaAs. Postoxidation Er ion implantation (1015 cm−2 and 300 keV) prevents the formation of nonradiative ErAs complexes, leading to a relatively long 1.53 μm fluorescence lifetime τ = 6.1 ms (an approximately seven times improvement) with approximately three times enhancement in the PL intensity. The data suggest that Er-doped AlGaAs native oxides formed using postoxidation implantation may be a viable active media for monolithic optoelectronic integration of waveguide amplifiers on GaAs substrates.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors

Hollow spiral phase plate for self-referenced spiral interferometry

X.-C. Yuan, N. Zhang, S. H. Tao, J. Bu, and J. Lin

Appl. Phys. Lett. 91, 171116 (2007); http://dx.doi.org/10.1063/1.2802576 (3 pages) | Cited 4 times

Online Publication Date: 25 October 2007

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The authors present experimental results of self-referenced spiral interference realized by a hollow spiral phase plate fabricated by electron beam lithography. Comparing with conventional interference systems, the proposed phase element provides a simple and robust approach to obtaining spiral interference fringes in a self-referenced interferometric way. Experimental implementation confirms that the element can be employed as an external tool kit for simple modification of existing optical microscopes to interferometers.
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07.60.Ly Interferometers
42.79.Ci Filters, zone plates, and polarizers
07.60.Pb Conventional optical microscopes

40 Gbit/s light signal transmission in long-range surface plasmon waveguides

Jung Jin Ju, Suntak Park, Min-su Kim, Jin Tae Kim, Seung Koo Park, Yoon Jung Park, and Myung-Hyun Lee

Appl. Phys. Lett. 91, 171117 (2007); http://dx.doi.org/10.1063/1.2803069 (3 pages) | Cited 28 times

Online Publication Date: 25 October 2007

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We demonstrate a high bit-rate optical signal transmission by using long-range surface plasmon polariton (LRSPP) waves in a guided geometry. With a 40 Gbit/s optical communication signal, eye patterns and bit-error-rates were measured to access the quality of the transmission properties of the LRSPP mode. A thin gold strip line embedded in a low loss optical polymer supports a LRSPP mode, which propagates with a 2 dB/cm loss, and couples to standard single mode fibers at 1.55 μm with a 2 dB coupling loss. A 40 Gbit/s optical signal was transmitted via a 4 cm long LRSPP waveguide without any distortion of the eye patterns. The experiment also showed error-free transmissions. These results indicate that the LRSPP waveguide is a potential transmission line for optical interconnections overcoming the inherent problems in electric interconnections.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Gn Optical waveguides and couplers

Common origin of ferromagnetism and band edge Zeeman splitting in GaMnAs at low Mn concentrations

R. Chakarvorty, S. Shen, K. J. Yee, T. Wojtowicz, R. Jakiela, A. Barcz, X. Liu, J. K. Furdyna, and M. Dobrowolska

Appl. Phys. Lett. 91, 171118 (2007); http://dx.doi.org/10.1063/1.2804561 (3 pages) | Cited 14 times

Online Publication Date: 26 October 2007

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We report magnetic circular dichroism measurements on thin GaMnAs films with low Mn concentration, which reveal that exchange-induced spin splitting of the band edges occurs only in samples that show ferromagnetic order, and is not observed in paramagnetic samples. These results lead to the conclusion that Mn ions in the A0 configuration (d5+hole) provide the only mechanism for exchange interaction between Mn spins and band carriers. We also show that there is a linear relation between the observed exchange-induced splitting of the band edges and the Curie temperature, pointing to a common origin of the band edge splitting and ferromagnetism in GaMnAs.
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75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
78.20.Ls Magneto-optical effects
78.66.Fd III-V semiconductors
75.70.Ak Magnetic properties of monolayers and thin films

Lossless all-optical phase gate using a polarization-division Sagnac interferometer applicable to a waveguide-type Kerr medium

Nobuyuki Matsuda, Yasuyoshi Mitsumori, Hideo Kosaka, Keiichi Edamatsu, and Ryosuke Shimizu

Appl. Phys. Lett. 91, 171119 (2007); http://dx.doi.org/10.1063/1.2801697 (3 pages) | Cited 4 times

Online Publication Date: 26 October 2007

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We propose an apparatus that realizes direct observation of nonlinear phase shifts induced by cross-phase modulation. The apparatus is based on a polarization-division Sagnac interferometer incorporating Faraday rotators, which, in principle, enables phase robustness, flexibility, and lossless operation. Here, we present the measurement of nonlinear phase shifts in a photonic crystal fiber, demonstrating the advantage of our system in its application to waveguide-type Kerr media. This apparatus is applicable to lossless all-optical phase gates and switches.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
07.60.Ly Interferometers
42.79.Gn Optical waveguides and couplers
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Qs Photonic bandgap materials

Thick film laser induced forward transfer for deposition of thermally and mechanically sensitive materials

Nicholas T. Kattamis, Priscilla E. Purnick, Ron Weiss, and Craig B. Arnold

Appl. Phys. Lett. 91, 171120 (2007); http://dx.doi.org/10.1063/1.2799877 (3 pages) | Cited 28 times

Online Publication Date: 26 October 2007

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Laser forward transfer processes incorporating thin absorbing films can be used to deposit robust organic and inorganic materials but the deposition of more delicate materials has remained elusive due to contamination and stress induced during the transfer process. Here, we present the approach to high resolution patterning of sensitive materials by incorporating a thick film polymer absorbing layer that is able to dissipate shock energy through mechanical deformation. Multiple mechanisms for transfer as a function of incident laser energy are observed and we show viable and contamination-free deposition of living mammalian embryonic stem cells.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.16.Rf Micro- and nanoscale pattern formation
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
87.85.Lf Tissue engineering
87.17.-d Cell processes

Particle separation and collection using an optical chromatographic filter

Sean J. Hart, Alex V. Terray, and Jonathan Arnold

Appl. Phys. Lett. 91, 171121 (2007); http://dx.doi.org/10.1063/1.2799180 (3 pages) | Cited 12 times

Online Publication Date: 26 October 2007

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An optofluidic design has been used to completely separate and collect fractions of an injected mixture of colloidal particles. A three-dimensional glass microfluidic device was constructed such that the fluid was directed though a 50-μm-diameter channel. A laser was introduced opposite the flow and its spot size adjusted to completely fill the channel. Thus, for a given laser power and flow rate, certain particles are completely retained while others pass through unhindered. Separation efficiencies in excess of 99% have been attained for a mixture of polymer and silica beads.
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82.80.Bg Chromatography
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