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14 Apr 2008

Volume 92, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 92, 153101 (2008); http://dx.doi.org/10.1063/1.2907577 (3 pages)

H. Mino, Y. Kouno, K. Oto, K. Muro, R. Akimoto, and S. Takeyama
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Floating electrode optoelectronic tweezers: Light-driven dielectrophoretic droplet manipulation in electrically insulating oil medium

Sungyong Park, Chenlu Pan, Ting-Hsiang Wu, Christoph Kloss, Sheraz Kalim, Caitlin E. Callahan, Michael Teitell, and Eric P. Y. Chiou

Appl. Phys. Lett. 92, 151101 (2008); http://dx.doi.org/10.1063/1.2906362 (3 pages) | Cited 17 times

Online Publication Date: 14 April 2008

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We report an optical actuation mechanism, floating electrode optoelectronic tweezers (FEOET). FEOET enables light-driven transport of aqueous droplets immersed in electrically insulating oil on a featureless photoconductive glass layer with direct optical images. We demonstrate that a 681 μm de-ionized water droplet immersed in corn oil medium is actuated by a 3.21 μW laser beam with an average intensity as low as 4.08 μW/mm2 at a maximum speed of 85.1 μm/s on a FEOET device. FEOET provides a promising platform for massively parallel droplet manipulation with optical images on low cost, silicon-coated glass. The FEOET device structure, fabrication, working principle, numerical simulations, and operational results are presented in this letter.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
47.55.D- Drops and bubbles
87.15.Tt Electrophoresis

Enhanced near-infrared emission from Ni2+ in Cr3+/Ni2+ codoped transparent glass ceramics

Botao Wu, Shifeng Zhou, Jian Ruan, Yanbo Qiao, Danping Chen, Congshan Zhu, and Jianrong Qiu

Appl. Phys. Lett. 92, 151102 (2008); http://dx.doi.org/10.1063/1.2909543 (3 pages) | Cited 6 times

Online Publication Date: 14 April 2008

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Transparent Li2O–Ga2O3–SiO2 glass ceramics containing Cr3+/Ni2+ codoped LiGa5O8 nanocrystals were synthesized. The steady state emission spectra indicated that the near-infrared emission intensity of Ni2+ at 1300 nm in Cr3+/Ni2+ codoped glass ceramics was enhanced up to about 7.3 times compared with that in Ni2+ single-doped glass ceramics with 532 nm excitation. This enhancement in emission intensity was due to efficient energy transfer from Cr3+ to Ni2+, which was confirmed by time-resolved emission spectra. The energy transfer efficiency was estimated to be 85% and the energy transfer mechanism was discussed.
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42.70.Ce Glasses, quartz
78.55.Hx Other solid inorganic materials
78.55.Qr Amorphous materials; glasses and other disordered solids
78.47.jd Time resolved luminescence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Exploration of the surface director profile in a liquid crystal cell using coupling between the surface plasmon and half-leaky optical guided modes

Fuzi Yang, Lizhen Ruan, and J. R. Sambles

Appl. Phys. Lett. 92, 151103 (2008); http://dx.doi.org/10.1063/1.2908224 (3 pages) | Cited 1 time

Online Publication Date: 15 April 2008

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The half-leaky guided mode geometry with a thin metal tunnel barrier as one cladding layer is used to explore the distribution of the director very near to the surface in a hybrid aligning nematic liquid crystal cell. From theoretical analysis together with numerical modeling, it is shown how the coupled p-polarized surface plasmon/s-like guided modes excited in the geometry leads to extremely sensitive to the surface director tilt profile near the metal wall—a sensitivity which is even higher than that of the surface plasmon resonance alone. The experimental results have fully confirmed the model predictions.
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61.30.-v Liquid crystals
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys

High-speed all-optical modulation using polycrystalline silicon microring resonators

Kyle Preston, Po Dong, Bradley Schmidt, and Michal Lipson

Appl. Phys. Lett. 92, 151104 (2008); http://dx.doi.org/10.1063/1.2908869 (3 pages) | Cited 23 times

Online Publication Date: 15 April 2008

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We experimentally demonstrate on-chip active photonic devices fabricated from deposited polycrystalline silicon, which can be used for monolithic three-dimensional integration of optical networks. The demonstrated modulator is based on all-optical carrier injection in a micrometer-size resonator and has a modulation depth of 10 dB and a temporal response of 135 ps. Grain boundaries in the polycrystalline silicon (polysilicon) material result in faster electron-hole recombination, enabling a shortened carrier lifetime and a faster optical switching time compared to similar devices based on crystalline silicon.
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42.70.Qs Photonic bandgap materials
42.65.Pc Optical bistability, multistability, and switching, including local field effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Mm Grain and twin boundaries

Spectral and temporal response of liquid-crystal-on-silicon spatial light modulators

Martin Bock, Susanta Kumar Das, Ruediger Grunwald, Stefan Osten, Peter Staudt, and Gero Stibenz

Appl. Phys. Lett. 92, 151105 (2008); http://dx.doi.org/10.1063/1.2909115 (3 pages) | Cited 14 times

Online Publication Date: 15 April 2008

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Spectral and temporal phase response of selected types of liquid-crystal-on-silicon spatial light modulators were studied using femtosecond pulses, determining specific transfer functions of the devices. The phase response resulting from programed gray level distributions was detected by analyzing the diffraction characteristics and by spectral phase interferometry for direct electric-field reconstruction. The results indicate the appearance of distinct parameter ranges that enable minimum spatiotemporal distortion. Weak oscillations in the spectral phase are explained by Gires–Tournois resonances [ F. Gires and P. Tournois, Acad. Sci. Paris, C. R. 258, 6112 (1964) ].
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42.79.Kr Display devices, liquid-crystal devices

Coupling length of silicon-on-insulator directional couplers probed by Fourier-space imaging

J. Jágerská, N. Le Thomas, R. Houdré, D. M. Beggs, D. O’Brien, and T. F. Krauss

Appl. Phys. Lett. 92, 151106 (2008); http://dx.doi.org/10.1063/1.2909575 (3 pages)

Online Publication Date: 15 April 2008

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We use a Fourier-space imaging technique relying on outcoupling grating probes to study the coupled mode interaction and dispersion properties of guided modes in silicon-on-insulator codirectional couplers. Our approach allows us to measure the mode splitting inherent to coupled systems, determine the mode symmetry, and locally probe the coupling length with an accuracy of ±50 nm. A systematic study of directional couplers with different waveguide widths, coupling gaps, and e-beam exposure doses is reported in order to verify the results across a wider parameter space.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings

Wideband 15 THz response using organic electro-optic polymer emitter-sensor pairs at telecommunication wavelengths

Colin V. McLaughlin, L. Michael Hayden, Brent Polishak, Su Huang, Jingdong Luo, Tae-Dong Kim, and Alex K.-Y. Jen

Appl. Phys. Lett. 92, 151107 (2008); http://dx.doi.org/10.1063/1.2909599 (3 pages) | Cited 27 times

Online Publication Date: 15 April 2008

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Poled polymer films are employed in terahertz emission and detection using telecommunication wavelength femtosecond pulses. Films 10–15 μm thick with electro-optic coefficients as high as 160 pm/V at 1300 nm are used to generate and sense subpicosecond pulses with continuous bandwidth up to 15 THz. Terahertz emission from a poled polymer film is compared to terahertz emission from the organic crystal DAST. The use of a poled polymer as the terahertz sensor allows the identification of DAST phonons at 1.1, 3.0, 5.3, 8.5, and 12.5 THz.
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42.70.Jk Polymers and organics
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Wc Optical coatings

Lasing from dye-doped photonic crystals with graded layers in dichromate gelatin emulsions

Mang Hin Kok, Weixin Lu, Jeffrey Chi Wai Lee, Wing Yim Tam, George K. L. Wong, and C. T. Chan

Appl. Phys. Lett. 92, 151108 (2008); http://dx.doi.org/10.1063/1.2907488 (3 pages) | Cited 6 times

Online Publication Date: 17 April 2008

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We report on optically pumped lasing from dye-doped, graded-spacing layer structures of dichromate gelatin emulsions fabricated using two-beam holographic interference. The graded layers exhibited deep and wide photonic band gaps. Multimode lasing with both a low threshold and a high quality factor was observed at the band edge of the photonic band gap. We modeled the emissions from the dye-doped graded layer system using a finite difference time domain technique and achieved good agreement with experimental results.
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42.55.Mv Dye lasers
42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.70.Hj Laser materials
42.60.By Design of specific laser systems
42.40.Kw Holographic interferometry; other holographic techniques

Single-photon level ultrafast all-optical switching

Xiao-Feng Han, Yu-Xiang Weng, Rui Wang, Xi-Hao Chen, Kai-Hong Luo, Ling-An Wu, and Jimin Zhao

Appl. Phys. Lett. 92, 151109 (2008); http://dx.doi.org/10.1063/1.2909540 (3 pages) | Cited 10 times

Online Publication Date: 17 April 2008

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We demonstrate an approach to all-optical switching, where a weak beam controls a strong beam, based on three-wave mixing optical parametric amplification in a nonlinear crystal. Ultrafast switching within 400 fs has been achieved with a 130 fs single-photon level switch beam containing, on average, 0.75 photon/pulse, which can turn on/off a signal pulse containing 5.9×108 photons. The transverse patterns for the on and off states are well defined and the switch has a large bandwidth of up to 10 nm.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Yj Optical parametric oscillators and amplifiers

Degradation of InGaN/GaN laser diodes analyzed by microphotoluminescence and microelectroluminescence mappings

M. Rossetti, T. M. Smeeton, W.-S. Tan, M. Kauer, S. E. Hooper, J. Heffernan, H. Xiu, and C. J. Humphreys

Appl. Phys. Lett. 92, 151110 (2008); http://dx.doi.org/10.1063/1.2908919 (3 pages) | Cited 8 times

Online Publication Date: 17 April 2008

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The degradation of InGaN/GaN laser diodes grown by molecular beam epitaxy is analyzed by using surface mapping of the photoluminescence emission on a micrometric scale, which allows the identification of failure regions. This, combined with the mapping of the electroluminescence, suggests two different mechanisms for laser degradation. Increased nonradiative recombination at specific sites along the crystal directions associated with the presence of dislocations lying in the basal plane near the active region is one of these. We also observe an increase in current injection nonuniformities with increasing aging time.
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42.55.Px Semiconductor lasers; laser diodes
78.60.Fi Electroluminescence
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Nonlinear measurement of mid-infrared absorption in AlOx waveguides

M. Ravaro, E. Guillotel, M. Le Dû, C. Manquest, X. Marcadet, S. Ducci, V. Berger, and G. Leo

Appl. Phys. Lett. 92, 151111 (2008); http://dx.doi.org/10.1063/1.2911747 (3 pages) | Cited 1 time

Online Publication Date: 17 April 2008

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We report a quantitative study on the absorption of oxidized-AlAs (AlOx) integrated thin layers in the mid-infrared range (2–4 μm). An AlOx absorption coefficient of 1600 cm−1 is measured in a nonlinear waveguide, by investigating the phase-matching bandwidth of parametric fluorescence. Since mid-infrared optical losses of the idler mode are inferred from the corresponding signal features in the 1–2 μm range, our technique takes advantage of common near-infrared sources and detectors.
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78.30.-j Infrared and Raman spectra
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Generation of nitrogen acceptors in ZnO using pulse thermal processing

Jun Xu, Ronald Ott, Adrian S. Sabau, Zhengwei Pan, Faxian Xiu, Jianlin Liu, Jean-Marie Erie, and David P. Norton

Appl. Phys. Lett. 92, 151112 (2008); http://dx.doi.org/10.1063/1.2911725 (3 pages) | Cited 6 times

Online Publication Date: 17 April 2008

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Bipolar doping in wide bandgap semiconductors is difficult to achieve under equilibrium conditions because of the spontaneous formation of compensating defects and unfavorable energetics for dopant substitution. In this work, we explored the use of rapid pulse thermal processing for activating nitrogen dopants into acceptor states in ZnO. Low-temperature photoluminescence spectra revealed both acceptor-bound exciton (A0X) and donor-acceptor pair emissions, which present direct evidence for acceptors generated after pulse thermal processing of nitrogen-doped ZnO. This work suggests that pulse thermal processing is potentially an effective method for p-type doping of ZnO.
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61.72.uj III-V and II-VI semiconductors
71.35.-y Excitons and related phenomena
71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors

In depth fiber optic trapping of low-index microscopic objects

K. S. Mohanty, C. Liberale, S. K. Mohanty, and V. Degiorgio

Appl. Phys. Lett. 92, 151113 (2008); http://dx.doi.org/10.1063/1.2908216 (3 pages) | Cited 14 times

Online Publication Date: 18 April 2008

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We demonstrate that a focused beam through a microaxicon built on the tip of a single mode optical fiber can trap low-index objects at much larger depths as compared to the vortex beam tweezers generated using high numerical aperture microscope objectives. The measured transverse trapping force for low-index objects in Mie regime was found to depend on particle size and on distance of trapped objects from the fiber tip. While axial movement of trapped low-index objects was achieved by variation in trap beam power, transportation in three dimensions was achieved by maneuvering the fiber.
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42.81.-i Fiber optics
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Metal-semiconductor-metal Ge photodetectors integrated in silicon waveguides

Laurent Vivien, Delphine Marris-Morini, Jean-Marc Fédéli, Mathieu Rouvière, Jean-François Damlencourt, Loubna El Melhaoui, Xavier Le Roux, Paul Crozat, Juliette Mangeney, Eric Cassan, and Suzanne Laval

Appl. Phys. Lett. 92, 151114 (2008); http://dx.doi.org/10.1063/1.2909590 (3 pages) | Cited 7 times

Online Publication Date: 18 April 2008

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Metal-semiconductor-metal (MSM) Ge photodetectors integrated in silicon-on-insulator waveguides using butt coupling configuration have been experimentally demonstrated. Bandwidths reach 28 GHz under 6 V bias at wavelengths of 1.31 and 1.55 μm for a photodetector with 1 μm electrode spacing, which is almost compatible with a 40 Gb/s operation. High responsivity of about 1 A/W at both wavelengths for a 10 μm long photodetector has been obtained. Under 1 V bias, MSM photodetectors with 1 and 0.7 μm electrode spacings have bandwidths of 9 and 17 GHz, respectively, which is compatible with a data transmission speed of 10 Gb/s.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.82.Et Waveguides, couplers, and arrays

Schottky-quantum dot photovoltaics for efficient infrared power conversion

Keith W. Johnston, Andras G. Pattantyus-Abraham, Jason P. Clifford, Stefan H. Myrskog, Dean D. MacNeil, Larissa Levina, and Edward H. Sargent

Appl. Phys. Lett. 92, 151115 (2008); http://dx.doi.org/10.1063/1.2912340 (3 pages) | Cited 63 times

Online Publication Date: 18 April 2008

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Planar Schottky photovoltaic devices were prepared from solution-processed PbS nanocrystal quantum dot films with aluminum and indium tin oxide contacts. These devices exhibited up to 4.2% infrared power conversion efficiency, which is a threefold improvement over previous results. Solar power conversion efficiency reached 1.8%. The simple, optimized architecture allows for direct implementation in multijunction photovoltaic device configurations.
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85.60.-q Optoelectronic devices

The influence of mobility unbalance on GaN based vertical cavity surface emitting lasers

E. Petrolati and A. Di Carlo

Appl. Phys. Lett. 92, 151116 (2008); http://dx.doi.org/10.1063/1.2913203 (3 pages) | Cited 4 times

Online Publication Date: 18 April 2008

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In this work, we discuss the influence of the large mobility difference between electrons and holes on the electrical injection properties of GaN based vertical cavity surface emitting lasers. This mobility unbalance is mainly responsible for the unfocusing of the electron and hole radiative recombination in the central region of the device where the electromagnetic field is confined.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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