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31 Mar 2008

Volume 92, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 92, 133501 (2008); http://dx.doi.org/10.1063/1.2901684 (3 pages)

Eric Akmansoy, Emmanuel Centeno, Kevin Vynck, David Cassagne, and Jean-Michel Lourtioz
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High efficiency diffractive grating couplers for interfacing a single mode optical fiber with a nanophotonic silicon-on-insulator waveguide circuit

G. Roelkens, D. Vermeulen, D. Van Thourhout, R. Baets, S. Brision, P. Lyan, P. Gautier, and J.-M. Fédéli

Appl. Phys. Lett. 92, 131101 (2008); http://dx.doi.org/10.1063/1.2905260 (3 pages) | Cited 42 times

Online Publication Date: 31 March 2008

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High efficiency diffractive grating structures to interface a single mode optical fiber and a nanophotonic integrated circuit fabricated on silicon-on-insulator are presented. The diffractive grating structures are designed to be inherently very directional by adding a silicon overlay before grating definition. 55% coupling efficiency at a wavelength of 1.53 μm is experimentally demonstrated on devices fabricated using standard complementary metal-oxide semiconductor technology. By optimizing the grating parameters, we theoretically show that 80% grating coupling efficiency can be obtained for a uniform grating structure.
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42.82.Et Waveguides, couplers, and arrays
42.81.Qb Fiber waveguides, couplers, and arrays
85.60.-q Optoelectronic devices

Spectrally smoothed supercontinuum generation by using unstably mode-locked laser pulses

Kebin Shi and Zhiwen Liu

Appl. Phys. Lett. 92, 131102 (2008); http://dx.doi.org/10.1063/1.2904619 (3 pages) | Cited 1 time

Online Publication Date: 31 March 2008

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We report on a simple approach to obtain spectrally smoothed supercontinuum (SC) by using unstably mode-locked femtosecond laser pulses. The spectrum smoothing effect is due to the averaging of the supercontinua generated in a nonlinear photonic crystal fiber by modulated pulses. Theoretical analysis based upon solving the generalized nonlinear Schrödinger equation is presented, which qualitatively agrees well with the experimental observation. Finally, the application of the smoothed SC to broadband coherent anti-Stokes Raman scattering spectroscopy is demonstrated, which can result in a relatively smooth nonresonant background and suppress spurious peaks.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
42.81.-i Fiber optics
42.70.Qs Photonic bandgap materials
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

Two-port vectorial terahertz electro-optic sampling system

L. Meignien, J. Mangeney, P. Crozat, L. Duvillaret, and M. Hanna

Appl. Phys. Lett. 92, 131103 (2008); http://dx.doi.org/10.1063/1.2904620 (3 pages) | Cited 4 times

Online Publication Date: 31 March 2008

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We present a fiber-based two-port terahertz electro-optic (EO) sampling system at 1.55 μm wavelength, including an ultrafast In0.53Ga0.47As photoconductive switch and a freely positionable prismatic EO probe. Frequency components are extended up to 2 THz and the dynamic range is larger than 40 dB, regardless of the direction of the electromagnetic wave propagating in the waveguide, thanks to the two-port system. The symmetrical two-port pigtailed EO probe allows to determine the direction of propagation of the guided picosecond electromagnetic pulses.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
85.60.Bt Optoelectronic device characterization, design, and modeling

An alternative of spectroscopic ellipsometry: The double-reference method

I. Kézsmárki and S. Bordács

Appl. Phys. Lett. 92, 131104 (2008); http://dx.doi.org/10.1063/1.2904623 (3 pages)

Online Publication Date: 31 March 2008

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We have developed a method conceptually different from ellipsometric techniques which allows the determination of the complex refractive index by simultaneously measuring the unpolarized normal-incidence reflectivity relative to the vacuum and another reference media such as diamond, GaAs, CdTe, etc. From these two quantities, the complex optical response can be directly obtained without Kramers–Kronig transformation. Due to its transparency and large refractive index from the far-infrared to the soft ultraviolet regions, diamond can be ideally used as a second reference over the whole optical spectrum. The experimental arrangement is rather simple compared to ellipsometry.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)

Mechanisms of subdiffraction free-space imaging using a transmission-line metamaterial superlens: An experimental verification

Ashwin K. Iyer and George V. Eleftheriades

Appl. Phys. Lett. 92, 131105 (2008); http://dx.doi.org/10.1063/1.2904635 (3 pages) | Cited 10 times

Online Publication Date: 31 March 2008

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This work presents experimental verification of free-space subdiffraction imaging using a Veselago-Pendry superlens [Sov. Phys. Usp. 10, 509 (1968); Phys. Rev. Lett. 85, 3966 (2000) ] based on the negative-refractive-index transmission-line approach. The superlens is able to resolve two sources λ0/3 apart not only at the design frequency of 2.40 GHz, where the metamaterial possesses μ and ϵ equal to −μ0 and −ϵ0, respectively, but also at 2.08 GHz, where the metamaterial experiences a resonance in μ.
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42.79.Bh Lenses, prisms and mirrors
42.70.-a Optical materials

Near-field scanning optical microscopy with monolithic silicon light emitting diode on probe tip

Kazunori Hoshino, Lynn J. Rozanski, David A. Vanden Bout, and Xiaojing Zhang

Appl. Phys. Lett. 92, 131106 (2008); http://dx.doi.org/10.1063/1.2904698 (3 pages) | Cited 7 times

Online Publication Date: 31 March 2008

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We describe optical and topographic imaging using a light emitting diode monolithically integrated on a silicon probe tip for near-field scanning optical microscopy (NSOM). The light emission resulted from a silicon dioxide layer buried between a phosphorus-doped N+ silicon layer and a gallium-doped P+ silicon region locally created at the tip by a focused ion beam. The tip was employed in a standard NSOM excitation setup. The probe successfully measured optical as well as topographic images of a chromium test pattern with imaging resolutions of 400 and 50 nm, respectively. The directional resolution dependence of the acquired images directly corresponds to the shape, size, and polarity of the light source on the probe tip. To our knowledge, this report is the first successful near-field imaging result directly measured by such tip-embedded light sources.
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07.79.Fc Near-field scanning optical microscopes
85.60.Jb Light-emitting devices
42.30.Va Image forming and processing
42.82.Gw Other integrated-optical elements and systems

In-line phase-contrast imaging of a biological specimen using a compact laser-Compton scattering-based x-ray source

H. Ikeura-Sekiguchi, R. Kuroda, M. Yasumoto, H. Toyokawa, M. Koike, K. Yamada, F. Sakai, K. Mori, K. Maruyama, H. Oka, and T. Kimata

Appl. Phys. Lett. 92, 131107 (2008); http://dx.doi.org/10.1063/1.2903148 (3 pages) | Cited 14 times

Online Publication Date: 1 April 2008

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Laser-Compton scattering (LCS) x-ray sources have recently attracted much attention for their potential use at local medical facilities because they can produce ultrashort pulsed, high-brilliance, and quasimonochromatic hard x rays with a small source size. The feasibility of in-line phase-contrast imaging for a “thick” biological specimens of rat lumbar vertebrae using the developed compact LCS-X in AIST was investigated for the promotion of clinical imaging. In the higher-quality images, anatomical details of the spinous processes of the vertebrae are more clearly observable than with conventional absorption radiography. The results demonstrate that phase-contrast radiography can be performed using LCS-X.
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87.59.B- Radiography
42.55.Vc X- and γ-ray lasers
87.57.cj Contrast

Optical loss in silicon microphotonic waveguides induced by metallic contamination

Tymon Barwicz, Charles W. Holzwarth, Peter T. Rakich, Miloš A. Popović, Erich P. Ippen, and Henry I. Smith

Appl. Phys. Lett. 92, 131108 (2008); http://dx.doi.org/10.1063/1.2903714 (3 pages) | Cited 1 time

Online Publication Date: 1 April 2008

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Propagation losses are paramount to the performance of microphotonic devices. In silicon photonics, the expected contribution of known propagation-loss mechanisms is often insufficient to account for all the observed loss. Here, we identify a loss mechanism that we believe has not yet been reported in the literature. We observe loss reaching 70 dB/cm in silicon wire waveguides patterned in proximity of metals with low temperatures of silicide formation. The loss is attributed to formation of a dilute silicide at the waveguide sidewalls during reactive-ion etching. Sputtered metal atoms originate from exposed metal on the wafer surface or from the reactive-ion etcher chamber and react with the bare silicon of the waveguide sidewall being formed.
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42.79.Gn Optical waveguides and couplers
42.82.-m Integrated optics

All-optical signal amplification in multiple-quantum-well resonant photonic bandgap structures

S. Schumacher, N. H. Kwong, and R. Binder

Appl. Phys. Lett. 92, 131109 (2008); http://dx.doi.org/10.1063/1.2904696 (3 pages) | Cited 4 times

Online Publication Date: 1 April 2008

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Using a microscopic many-particle theory, we predict all-optical amplification of low-intensity light pulses in resonant photonic bandgap structures realized by Bragg-spaced semiconductor multiple quantum wells. The discussed scheme is based on mirrorless parametric amplification.
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42.65.Lm Parametric down conversion and production of entangled photons
42.70.Qs Photonic bandgap materials

Continuous wave operation of a spiral-shaped microcavity laser

Chil-Min Kim, Jinhang Cho, Jinhyung Lee, Sunghwan Rim, Sang Hun Lee, Kwang Ryung Oh, and Jong Hoi Kim

Appl. Phys. Lett. 92, 131110 (2008); http://dx.doi.org/10.1063/1.2902174 (3 pages) | Cited 14 times

Online Publication Date: 2 April 2008

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We report a continuous wave laser output of a spiral-shaped InGaAs microcavity laser. When the boundary of the cavity is selectively pumped by current injection with a dc current, the laser generates a directional emission around the notch. We investigate the characteristics of the cw laser operation and observe whispering gallery type modes, whose Q factor is about 7000.
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42.55.Sa Microcavity and microdisk lasers

Magnetic resonance hybridization and optical activity of microwaves in a chiral metamaterial

T. Q. Li, H. Liu, T. Li, S. M. Wang, F. M. Wang, R. X. Wu, P. Chen, S. N. Zhu, and X. Zhang

Appl. Phys. Lett. 92, 131111 (2008); http://dx.doi.org/10.1063/1.2905285 (3 pages) | Cited 29 times

Online Publication Date: 2 April 2008

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The propagation of microwaves through a chiral metamaterial based on a magnetic dimer is experimentally studied. As proposed by our previous theoretical model, two resonance peaks are obtained in the transmission spectrum; these originate from the hybridization effect of magnetic resonance modes in this system. Optical activity is also observed in the transmission wave. The polarization state dramatically changes around the resonance frequency: the transmitted wave becomes elliptically polarized with its major polarization axis approximately perpendicular to that of the linear incident wave. This coupled magnetic dimer system provides a practical method to optically design tunable active medium and device.
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78.20.Ek Optical activity
78.70.Gq Microwave and radio-frequency interactions
42.70.-a Optical materials

High performance bi-dimensional resonant grating filter at 850 nm under high oblique incidence of ∼ 60°

S. Hernandez, O. Gauthier-Lafaye, A.-L. Fehrembach, S. Bonnefont, P. Arguel, F. Lozes-Dupuy, and A. Sentenac

Appl. Phys. Lett. 92, 131112 (2008); http://dx.doi.org/10.1063/1.2905295 (3 pages) | Cited 5 times

Online Publication Date: 2 April 2008

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We present an experimental demonstration of a polarization quasi-independent narrow-band (less than 0.8 nm) filter operating under high oblique incidence. The structure is a resonant grating with a hexagonal lattice which has been carefully designed to ensure polarization quasi-independence of the narrow-band resonance peak over a wide angular range around 60° of incidence. A good agreement between experimental results and theoretical calculations is shown.
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42.79.Dj Gratings
42.79.Ci Filters, zone plates, and polarizers
42.25.Ja Polarization

Control of optical mode distribution through etched microstructures for improved broad area laser performance

P. Crump, P. Leisher, T. Matson, V. Anderson, D. Schulte, J. Bell, J. Farmer, M. DeVito, R. Martinsen, Y. K. Kim, K. D. Choquette, G. Erbert, and G. Tränkle

Appl. Phys. Lett. 92, 131113 (2008); http://dx.doi.org/10.1063/1.2906030 (3 pages) | Cited 5 times

Online Publication Date: 2 April 2008

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Etching microstructures into broad area diode lasers is found to lead to more uniform near field and increased power conversion efficiency, arising from increased slope. Self-consistent device simulation indicates that this improvement is due to an increase in the effective internal injection efficiency above threshold—the nonuniform near field leads to regions of inefficient clamping of the carrier density in the laser stripe. Measurements of spontaneous emission through the substrate confirm the predicted carrier profile. Both experiment and theory show that improved overlap between carrier and power distributions correlates with improved slope.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.30.De Semiconductor-device characterization, design, and modeling

Direct observation of three-photon resonance in water-soluble ZnS quantum dots

Jun He, Gregory D. Scholes, Yu Long Ang, Wei Ji, Cyrus W. J. Beh, and Wee Shong Chin

Appl. Phys. Lett. 92, 131114 (2008); http://dx.doi.org/10.1063/1.2906904 (3 pages) | Cited 5 times

Online Publication Date: 2 April 2008

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We report on large three-photon absorption (3PA) in thioglycol-capped ZnS semiconductor quantum dots (QDs) at different wavelengths with femtosecond Z-scan technique. Both the intrinsic 3PA coefficients and cross sections of the 1.3 nm sized ZnS QDs in aqueous solution are nearly one order of magnitude greater than that of ZnS bulk crystal. The 3PA resonance in ZnS QDs is observed at the lowest excitonic transition of 1S(e)-1S3/2(h).
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78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
73.21.La Quantum dots

A route to increase the enhancement factor of surface enhanced Raman scattering (SERS) via a high density Ag flower-like pattern

Jixiang Fang, Yan Yi, Bingjun Ding, and Xiaoping Song

Appl. Phys. Lett. 92, 131115 (2008); http://dx.doi.org/10.1063/1.2895639 (3 pages) | Cited 24 times

Online Publication Date: 3 April 2008

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We explored a route to prepare a high enhancement factor of SERS substrate via a high density of Ag flowerlike pattern. The finite difference time domain (FDTD) calculations indicate that the Ag flowerlike pattern may demonstrate a high quality SERS property owing to the high density and abundant hot spot characteristic. Using an unusually high overpotential with electrodeposition system, the fractal flowerlike patterns and the high density nanoparticle arrays were experimental synthesized. The SERS measurement of above different Ag nanostructures verified the predications from the FDTD calculation.
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78.30.Er Solid metals and alloys
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.Pq Electrodeposition, electroplating
81.07.-b Nanoscale materials and structures: fabrication and characterization

Imaging with a 90 frames/s microbolometer focal plane array and high-power terahertz free electron laser

M. A. Dem’yanenko, D. G. Esaev, B. A. Knyazev, G. N. Kulipanov, and N. A. Vinokurov

Appl. Phys. Lett. 92, 131116 (2008); http://dx.doi.org/10.1063/1.2898138 (3 pages) | Cited 14 times

Online Publication Date: 3 April 2008

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An uncooled microbolometer focal plane array (FPA) has been developed and used for imaging of objects illuminated by monochromatic coherent radiation of a free electron laser tunable in the range of 1.25–2.5 THz. A sensitivity threshold of 1.3×10−3 W/cm2 was obtained for the FPA with a homemade absolute interferometric power meter. Videos up to 90 frames/s were recorded in both transmission and reflection/scattering modes. When objects were illuminated by laser radiation scattered by a rough metal surface, speckled images were observed. Good quality terahertz images were achieved through the fast rotation of the scatterer.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.10.Cm Micromechanical devices and systems
42.79.Pw Imaging detectors and sensors
41.60.Cr Free-electron lasers
42.60.-v Laser optical systems: design and operation
42.30.Ms Speckle and moiré patterns

1.55 μm ultrafast photoconductive switches based on ErAs:InGaAs

F. Ospald, D. Maryenko, K. von Klitzing, D. C. Driscoll, M. P. Hanson, H. Lu, A. C. Gossard, and J. H. Smet

Appl. Phys. Lett. 92, 131117 (2008); http://dx.doi.org/10.1063/1.2907335 (3 pages) | Cited 10 times

Online Publication Date: 3 April 2008

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The electron capture time in superlattice structures consisting of periodically spaced layers of self-assembled ErAs nanoislands and In0.53Ga0.47As is investigated on photoconductive switches as a function of the superlattice period using photocurrent autocorrelation and pulsed laser excitation at 1.55 μm. The capture time can be tuned from picoseconds all the way down to 0.2 ps by changing the periodicity. Two different Be doping schemes are explored to reduce the dark current. The resulting characteristics indicate that ErAs:InGaAs may serve as a high performance photoconductive material at this wavelength for pulsed terahertz emission and detection.
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85.60.-q Optoelectronic devices

The physical picture and the essential elements of the dynamical process for dispersive cloaking structures

Zixian Liang, Peijun Yao, Xiaowei Sun, and Xunya Jiang

Appl. Phys. Lett. 92, 131118 (2008); http://dx.doi.org/10.1063/1.2840703 (3 pages) | Cited 24 times

Online Publication Date: 4 April 2008

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We investigate the dynamical process of dispersive cloak by finite-difference time-domain numerical experiments. We find that there is a strong scattering process before achieving the stable state and its time length can be tuned by the dispersive strength. Poynting-vector directions show that the stable cloaking state is constructed locally while an intensity front sweeps through the cloak. Deeper studies demonstrate that the group velocity tangent component Vgθ is the dominant element in the process. This study is helpful not only for clear physical pictures but also for designing better cloaks to defend pulsive radars.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
02.70.Bf Finite-difference methods

Whispering gallery modes in hollow cylindrical microcavities containing silicon nanocrystals

J. R. Rodríguez, J. G. C. Veinot, P. Bianucci, and A. Meldrum

Appl. Phys. Lett. 92, 131119 (2008); http://dx.doi.org/10.1063/1.2903134 (3 pages) | Cited 5 times

Online Publication Date: 4 April 2008

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See Also: Publisher's Note

Show Abstract
A straightforward and inexpensive solution-based method to coat cylindrical microcavities with silicon nanocrystals is described. By using this method, high-quality films of oxide-embedded silicon nanocrystals (Si-ncs) were formed on the inner wall of hollow glass fibers. The resulting films were uniform and crack-free over lengths of 2–3 cm and were strongly luminescent due to the presence of well-passivated Si-ncs. The optical confinement provided by the film gave rise to resonant modes in the photoluminescence spectrum, with high-quality factors compared to Si-ncs in planar microcavities or microdisks or coated on glass spheres.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
81.07.Bc Nanocrystalline materials
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