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6 Feb 2012

Volume 100, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 061101 (2012); http://dx.doi.org/10.1063/1.3665180 (3 pages)

I. E. Khodasevych, C. M. Shah, S. Sriram, M. Bhaskaran, W. Withayachumnankul, B. S. Y. Ung, H. Lin, W. S. T. Rowe, D. Abbott, and A. Mitchell
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Elastomeric silicone substrates for terahertz fishnet metamaterials

I. E. Khodasevych, C. M. Shah, S. Sriram, M. Bhaskaran, W. Withayachumnankul, B. S. Y. Ung, H. Lin, W. S. T. Rowe, D. Abbott, and A. Mitchell

Appl. Phys. Lett. 100, 061101 (2012); http://dx.doi.org/10.1063/1.3665180 (3 pages) | Cited 6 times

Online Publication Date: 6 February 2012

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In this work, we characterize the electromagnetic properties of polydimethylsiloxane (PDMS) and use this as a free-standing substrate for the realization of flexible fishnet metamaterials at terahertz frequencies. Across the 0.2–2.5 THz band, the refractive index and absorption coefficient of PDMS are estimated as 1.55 and 0–22 cm−1, respectively. Electromagnetic modeling, multi-layer flexible electronics microfabrication, and terahertz time-domain spectroscopy are used in the design, fabrication, and characterization of the metamaterials, respectively. The properties of PDMS add a degree of freedom to terahertz metamaterials, with the potential for tuning by elastic deformation or integrated microfluidics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics
78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Terahertz magnetic field induced coherent spin precession in YFeO3

Runze Zhou, Zuanming Jin, Gaofang Li, Guohong Ma, Zhenxiang Cheng, and Xiaolin Wang

Appl. Phys. Lett. 100, 061102 (2012); http://dx.doi.org/10.1063/1.3682082 (4 pages) | Cited 3 times

Online Publication Date: 6 February 2012

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We present the magnetic dipole transition at 0.299 THz excited by magnetic component of terahertz electromagnetic pulse in an antiferromagnetic YFeO3 crystal. The impulsive magnetic field of the terahertz pulse tilts the macroscopic magnetization, causing deviation from the equilibrium position, which is manifested by a sharp absorption at the frequency of the quasiferromagnetic mode of the crystal. The rotating coherent macroscopic magnetization radiates elliptically polarized emission at the frequency of the quasiferromagnetic resonance due to the dichroic absorption in the crystal.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
78.20.Fm Birefringence
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics

Two-dimensional electrostatic lattices for indirect excitons

M. Remeika, M. M. Fogler, L. V. Butov, M. Hanson, and A. C. Gossard

Appl. Phys. Lett. 100, 061103 (2012); http://dx.doi.org/10.1063/1.3682302 (4 pages) | Cited 3 times

Online Publication Date: 6 February 2012

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We report on a method for the realization of two-dimensional electrostatic lattices for excitons using patterned interdigitated electrodes. Lattice structure is set by the electrode pattern and depth of the lattice potential is controlled by applied voltages. We demonstrate square, hexagonal, and honeycomb lattices created by this method.
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71.35.-y Excitons and related phenomena

Ultraviolet electroluminescence from colloidal ZnO quantum dots in an all-inorganic multilayer light-emitting device

T. Omata, Y. Tani, S. Kobayashi, K. Takahashi, A. Miyanaga, Y. Maeda, and S. Otsuka-Yao-Matsuo

Appl. Phys. Lett. 100, 061104 (2012); http://dx.doi.org/10.1063/1.3682307 (3 pages) | Cited 1 time

Online Publication Date: 6 February 2012

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We report ultraviolet (UV) electroluminescence (EL) at 3.30 eV of colloidal ZnO quantum dots (QDs) in an inorganic multilayer thin-film EL device. The EL spectrum was identical to the photoluminescence spectrum of the source solution of ZnO QDs, and the emission is attributable to quantum confined electron hole pair recombination. The UV emission was successful when the ZnO QD layer was sandwiched by thin MgO layers, while only a defect-related visible emission appeared without MgO layers. The type-I quantum well structure of MgO/ZnO/MgO and surface passivation of ZnO QDs by MgO must be important for the UV EL emission.
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85.60.Jb Light-emitting devices

Analysis of Gouy phase shift for optimizing terahertz air-biased-coherent-detection

Huanyu He and X.-C. Zhang

Appl. Phys. Lett. 100, 061105 (2012); http://dx.doi.org/10.1063/1.3682517 (4 pages) | Cited 3 times

Online Publication Date: 6 February 2012

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Terahertz (THz) air-biased-coherent-detection (ABCD) uses a local oscillator to enhance THz-wave detection sensitivity by mixing an optical field, a THz field, and a biased electric field (local oscillator) in air. The width of the electrodes providing the local oscillator, the longitudinal distribution of the optical and THz waves, both play important roles in the overall detection sensitivity. By analyzing the effect of the Gouy phase shift on the electric field distribution at the mixing location, we determine the optimal electrode width and observe an enhancement of the detection efficiency by a factor of two relative to the traditional THz-ABCD system using thin-wire electrodes.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
84.30.Ng Oscillators, pulse generators, and function generators

Electrically driven nanopyramid green light emitting diode

S.-P. Chang, Y.-C. Chen, J.-K. Huang, Y.-J. Cheng, J.-R. Chang, K.-P. Sou, Y.-T. Kang, H.-C. Yang, T.-C. Hsu, H.-C. Kuo, and C.-Y. Chang

Appl. Phys. Lett. 100, 061106 (2012); http://dx.doi.org/10.1063/1.3681363 (4 pages) | Cited 1 time

Online Publication Date: 7 February 2012

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An electrically driven nanopyramid green light emitting diode (LED) was demonstrated. The nanopyramid arrays were fabricated from a GaN substrate by patterned nanopillar etch, pillar side wall passivation, and epitaxial regrowth. Multiple quantum wells were selectively grown on the facets of the nanopyramids. The fabricated LED emits green wavelength under electrical injection. The emission exhibits a less carrier density dependent wavelength shift and higher internal quantum efficiency as compared with a reference c-plane sample at the same wavelength. It shows a promising potential for using nanopyramid in high In content LED applications.
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85.60.Jb Light-emitting devices

ZnO nanorods-graphene hybrid structures for enhanced current spreading and light extraction in GaN-based light emitting diodes

Jung Min Lee, Jaeseok Yi, Won Woo Lee, Hae Yong Jeong, Taeil Jung, Youngchae Kim, and Won Il Park

Appl. Phys. Lett. 100, 061107 (2012); http://dx.doi.org/10.1063/1.3683484 (5 pages) | Cited 6 times

Online Publication Date: 7 February 2012

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One-dimensional and two-dimensional hybrid structures, composed of vertical ZnO nanorods grown on large-area graphene, are successfully integrated onto the GaN/InGaN light emitting diodes (LEDs). Compared with GaN LED without transparent conducting electrode, current injection and light emission increased almost 2–3 times, respectively, by the introduction of graphene based conducting electrode. Additional ∼66% increase in light emission was achieved by growing the ZnO nanorods on the graphene, which is consistent with the finite difference time domain modeling result. Furthermore, electroluminescence intensity profiles confirm the uniform light emission with high brightness in GaN LED with the ZnO nanorods-graphene hybrid electrode.
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85.60.Jb Light-emitting devices

Fourier-transform photocurrent spectroscopy using a supercontinuum light source

Christian Petermann, Rene Beigang, and Peer Fischer

Appl. Phys. Lett. 100, 061108 (2012); http://dx.doi.org/10.1063/1.3683514 (3 pages) | Cited 1 time

Online Publication Date: 7 February 2012

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We demonstrate an implementation of frequency-encoded photocurrent spectroscopy using a super-continuum light source. The spectrally broad light is spatially dispersed and modulated with a special mechanical chopper design that permits a continuous wavelength-dependent modulation. After recombination, the light beam contains a frequency encoded spectrum which enables us to map the spectral response of a given sample in 60 ms and with a lateral resolution of 10 μm.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
79.60.-i Photoemission and photoelectron spectra
72.40.+w Photoconduction and photovoltaic effects
42.65.-k Nonlinear optics

Waveguide-integrated near-infrared detector with self-assembled metal silicide nanoparticles embedded in a silicon p-n junction

Shiyang Zhu, H. S. Chu, G. Q. Lo, P. Bai, and D. L. Kwong

Appl. Phys. Lett. 100, 061109 (2012); http://dx.doi.org/10.1063/1.3683546 (3 pages) | Cited 1 time

Online Publication Date: 7 February 2012

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An all-silicon photodetector integrated in a silicon-on-insulator waveguide for the telecom regime is proposed. The device is based on internal photoemission from electrically floating metal silicide nanoparticles (NPs) embedded in the space charge region of a Si p-n junction. Numerical simulation indicates that the light absorption could be enhanced if localized surface plasmon resonances are excited on the metal silicide nanoparticles, thus enabling to shrink the detector’s footprint to a submicron scale. A proof-of-concept detector fabricated using standard silicon complementary metal-oxide-semiconductor technology exhibits a peak responsivity of ∼30 mA/W at 5-V reverse bias and a 3-dB bandwidth of ∼6 GHz. It is expected that the overall performance would be significantly improved by optimization of both the detector’s configuration and the fabrication parameters.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.82.Et Waveguides, couplers, and arrays

X-ray spatial frequency heterodyne imaging

Binbin Wu, Yanan Liu, Christoph Rose-Petruck, and Gerald J. Diebold

Appl. Phys. Lett. 100, 061110 (2012); http://dx.doi.org/10.1063/1.3681794 (4 pages)

Online Publication Date: 7 February 2012

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We derive an expression for the electric field at the image plane from the Kirchhoff-Fresnel integral for a grating in contact with an object in an x-ray, in-line imaging configuration that shows the grating to give a heterodyning effect. We also show how image contrast in a harmonic of the grating is enhanced depending on the first space derivative of the phase function. Experiments are reported where a Fourier component of the image intensity gives contrast at the edges of objects significantly larger than that found with conventional in-line phase contrast imaging.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Sub-250 nm room-temperature optical gain from AlGaN/AlN multiple quantum wells with strong band-structure potential fluctuations

Emanuele Francesco Pecora, Wei Zhang, A. Yu. Nikiforov, Lin Zhou, David J. Smith, Jian Yin, Roberto Paiella, Luca Dal Negro, and T. D. Moustakas

Appl. Phys. Lett. 100, 061111 (2012); http://dx.doi.org/10.1063/1.3681944 (4 pages) | Cited 11 times

Online Publication Date: 7 February 2012

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Deep-UV optical gain has been demonstrated in Al0.7Ga0.3N/AlN multiple quantum wells under femtosecond optical pumping. Samples were grown by molecular beam epitaxy under a growth mode that introduces band structure potential fluctuations and high-density nanocluster-like features within the AlGaN wells. A maximum net modal gain value of 118 ± 9 cm−1 has been measured and the transparency threshold of 5 ± 1 µJ/cm2 was experimentally determined, corresponding to 1.4 × 1017 cm−3 excited carriers. These findings pave the way for the demonstration of solid-state lasers with sub-250 nm emission at room temperature.
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78.67.De Quantum wells
71.20.Nr Semiconductor compounds
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
78.40.Fy Semiconductors

Highly tunable whispering gallery mode semiconductor lasers with controlled absorber

A. N. Baranov, G. Boissier, R. Teissier, A. M. Monakhov, V. V. Sherstnev, M. I. Larchenkov, and Yu. P. Yakovlev

Appl. Phys. Lett. 100, 061112 (2012); http://dx.doi.org/10.1063/1.3682501 (4 pages)

Online Publication Date: 7 February 2012

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Tunable semiconductor lasers with controlled absorber based on GaInAsSb/GaAlAsSb quantum well heterostructure was fabricated and experimentally studied. The emission wavelength of these lasers shifts from 2.24 to 2.28 μm when the bias on the control contact decreases from the voltage equal to that on the main electrode to 0 V when the control contact is grounded. The principle of operation of such a device is given.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Nanometer sized Ni-dot/Ag/Pt structure for high reflectance of p-type contact metal in InGaN light emitting diodes

Kyu Sang Kim, Myoung Gyun Suh, and S. N. Cho

Appl. Phys. Lett. 100, 061113 (2012); http://dx.doi.org/10.1063/1.3685466 (3 pages)

Online Publication Date: 9 February 2012

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The Ni-dot/Ag/Pt layer, where Ni-dot layer is formed of nanometer sized Ni dots, has been used to improve the reflectivity from the surface of p-type GaN in a light emitting diode (LED). Comparing with Ni/Ag/Pt layer, where Ni layer is a thin film, the Ni-dot/Ag/Pt structure shows significantly improved reflectivity with stable contact resistivity. The optical output power and external quantum efficiency of InGaN LEDs with Ni-dot/Ag/Pt structure for p-metal have improved by 28% and 29%, respectively, over the results of Ni/Ag/Pt structure.
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85.60.Jb Light-emitting devices
73.40.Ns Metal-nonmetal contacts

Room temperature single photon emission from an epitaxially grown quantum dot

O. Fedorych, C. Kruse, A. Ruban, D. Hommel, G. Bacher, and T. Kümmell

Appl. Phys. Lett. 100, 061114 (2012); http://dx.doi.org/10.1063/1.3683498 (4 pages) | Cited 7 times

Online Publication Date: 9 February 2012

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Single photon emission from an epitaxially grown quantum dot at room temperature is presented. CdSe/ZnSSe quantum dots are embedded into MgS barriers, providing dominant radiative recombination up to 300 K. Under continuous wave optical excitation, the autocorrelation function g(2)(t) exhibits a sharp dip at (t = 0) with g(2)(0) = 0.16 ± 0.15 at T = 300 K, revealing excellent suppression of multiphoton emission even at room temperature.
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81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots
73.63.Kv Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Single photon emission from InGaN/GaN quantum dots up to 50 K

Stefan Kremling, Christian Tessarek, Heiko Dartsch, Stephan Figge, Sven Höfling, Lukas Worschech, Carsten Kruse, Detlef Hommel, and Alfred Forchel

Appl. Phys. Lett. 100, 061115 (2012); http://dx.doi.org/10.1063/1.3683521 (3 pages) | Cited 4 times

Online Publication Date: 9 February 2012

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We have investigated the optical properties of single InGaN quantum dots (QDs) by means of microphotoluminescence (μPL) spectroscopy. The QDs were grown on sapphire substrate using metal organic vapor phase epitaxy. Sharp and isolated single exciton emission lines in the blue spectral range were observed. The QD luminescence shows a strong degree of linear polarization up to 96% perpendicular to the growth axis (c-axis) with no preferential alignment in the xy plane. Second order autocorrelation measurements were performed under pulsed excitation and single photon emission up to 50 K is demonstrated.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
81.07.Ta Quantum dots
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.35.-y Excitons and related phenomena

Graphene induced tunability of the surface plasmon resonance

Jing Niu, Young Jun Shin, Youngbin Lee, Jong-Hyun Ahn, and Hyunsoo Yang

Appl. Phys. Lett. 100, 061116 (2012); http://dx.doi.org/10.1063/1.3683534 (4 pages) | Cited 6 times

Online Publication Date: 9 February 2012

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Tunability of the surface plasmon resonance wavelength is demonstrated by varying the thickness of Al2O3 spacer layer inserted between the graphene and nanoparticles. By varying the spacer layer thickness from 0.3 to 1.8 nm, the resonance wavelength is shifted from 583 to 566 nm. The shift is due to a change in the electromagnetic field coupling strength between the localized surface plasmons excited in the gold nanoparticles and a single layer graphene film. In contrast, when the graphene film is absent from the system, no noticeable shift in the resonance wavelength is observed upon varying the spacer thickness.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Resonant magnetic response of TiO2 microspheres at terahertz frequencies

H. Němec, C. Kadlec, F. Kadlec, P. Kužel, R. Yahiaoui, U.-C. Chung, C. Elissalde, M. Maglione, and P. Mounaix

Appl. Phys. Lett. 100, 061117 (2012); http://dx.doi.org/10.1063/1.3683540 (4 pages) | Cited 3 times

Online Publication Date: 9 February 2012

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Spray-drying technique is used to fabricate spherical microparticles out of dissolved TiO2 nanoparticles. We show both experimentally and through numerical calculations that the microspheres support a Mie resonance, leading to an effective magnetic response. For this purpose, nearly single layers of microspheres were prepared and characterized by time-domain terahertz spectroscopy. We developed an experimental approach allowing simultaneous measurement of complex transmittance and reflectance of a thin layer, which in turn enables evaluation of its effective dielectric permittivity and effective magnetic permeability. Numerical finite-element-method calculations of the electromagnetic response show that the prepared microparticles are suitable for preparing a metamaterial with negative effective magnetic permeability.
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81.07.Bc Nanocrystalline materials
78.70.Gq Microwave and radio-frequency interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Cd Fabrication of magnetic nanostructures
77.22.Ch Permittivity (dielectric function)

Optimizing conversion efficiency and reducing ion energy in a laser-produced Gd plasma

Thomas Cummins, Takamitsu Otsuka, Noboru Yugami, Weihua Jiang, Akira Endo, Bowen Li, Colm O’Gorman, Padraig Dunne, Emma Sokell, Gerry O’Sullivan, and Takeshi Higashiguchi

Appl. Phys. Lett. 100, 061118 (2012); http://dx.doi.org/10.1063/1.3684242 (4 pages) | Cited 3 times

Online Publication Date: 9 February 2012

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We have demonstrated an efficient extreme ultraviolet (EUV) source at 6.7 nm by irradiating Gd targets with 0.8 and 1.06 μm laser pulses of 140 fs to 10 ns duration. Maximum conversion efficiency of 0.4% was observed within a 0.6% bandwidth. A Faraday cup observed ion yield and time of flight signals for ions from plasmas generated by each laser. Ion kinetic energy was lower for shorter pulse durations, which yielded higher electron temperatures required for efficient EUV emission, due to higher laser intensity. Picosecond laser pulses were found to be the best suited to 6.7 nm EUV source generation.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Dg Plasma kinetic equations
52.80.Yr Discharges for spectral sources (including inductively coupled plasma)

Manifestation of quantum disordered wave functions with weak localization from conical second harmonic generation in ferroelectric crystal

H. H. Yu, H. J. Zhang, Z. P. Wang, H. H. Xu, Y. C. Wang, J. Y. Wang, and V. Petrov

Appl. Phys. Lett. 100, 061119 (2012); http://dx.doi.org/10.1063/1.3684252 (3 pages)

Online Publication Date: 9 February 2012

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The spatial structure of two-dimensional quantum disordered wave functions with weak localization (WL) is experimentally observed using a calcium barium niobate Ca0.28Ba0.72Nb2O6 (CBN-28) ferroelectric crystal illuminated by a pulsed laser beam. Non-collinear phase-matching in CBN-28 produces conical second harmonic pattern in the far-field. The probability density distribution of the experimental near-field pattern agrees very well with the theoretical predictions. The localization degree, within the error limits, is the same at different transverse positions due to the periodicity of the crystal and the eigenfunctions are degenerated. We conclude that a ferroelectric crystal represents an ideal model system for investigation of WL.
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42.50.-p Quantum optics
42.79.Nv Optical frequency converters
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
73.20.Fz Weak or Anderson localization
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

InGaN light‐emitting diodes with indium‐tin‐oxide sub‐micron lenses patterned by nanosphere lithography

Q. Zhang, K. H. Li, and H. W. Choi

Appl. Phys. Lett. 100, 061120 (2012); http://dx.doi.org/10.1063/1.3684505 (4 pages) | Cited 2 times

Online Publication Date: 9 February 2012

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Close‐packed micro‐lenses with dimensions of the order of wavelength have been integrated onto the indium‐tin‐oxide (ITO) layer of GaN light‐emitting diodes employing nanosphere lithography. The ITO lens arrays are transferred from a self‐assembled silica nanosphere array by dry etching, leaving the semiconductor layer damage‐free. An enhancement of up to 63.5% on optical output power from the lensed light‐emitting diode (LED) has been observed. Lens‐patterned LEDs are also found to exhibit reduced emission divergence. Three‐dimensional finite‐difference time‐domain simulations performed for light extraction and emission characteristics are found to be consistent with the observed results.
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85.60.Jb Light-emitting devices
81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly
02.70.Bf Finite-difference methods

Epitaxial growth and demonstration of hexagonal BN/AlGaN p-n junctions for deep ultraviolet photonics

S. Majety, J. Li, X. K. Cao, R. Dahal, B. N. Pantha, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 100, 061121 (2012); http://dx.doi.org/10.1063/1.3682523 (4 pages) | Cited 2 times

Online Publication Date: 9 February 2012

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Recent advances in epitaxial growth and demonstration of p-type conductivity in hexagonal boron nitride (hBN) epilayers represent an exceptional opportunity to revolutionize p-layer approach and overcome the intrinsic problem of low p-type conductivity in Al-rich AlGaN for deep ultraviolet (DUV) device applications. Nevertheless, the ability of epitaxial growth of hBN on AlGaN is a prerequisite for the incorporation of p-type hBN in AlGaN DUV device structures. We report on the epi-growth of hBN on Al-rich AlGaN/AlN/Al2O3 templates using metal organic chemical vapor deposition. X-ray diffraction measurement revealed a 2θ peak at 26.5° which indicates that the BN epilayers are hexagonal and consist of a single phase. Mg doped hBN epilayers were also grown on highly insulating AlN and n-type AlGaN templates with an attempt to demonstrate hBN/AlGaN p-n junctions. Mg doped hBN epilayers grown on insulating templates were p-type with an in-plane resistivity of ∼2.3 Ω cm. Diode behavior in the p-n structures of p-hBN/n-AlxGa1−xN (x ∼ 0.62) has been demonstrated. The results here reveal the feasibility of using highly conductive p-type hBN as an electron blocking and p-contact layers for AlGaN deep UV emitters.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Enhanced spontaneous emission from quantum dots in short photonic crystal waveguides

Thang Ba Hoang, Johannes Beetz, Leonardo Midolo, Matthias Skacel, Matthias Lermer, Martin Kamp, Sven Höfling, Laurent Balet, Nicolas Chauvin, and Andrea Fiore

Appl. Phys. Lett. 100, 061122 (2012); http://dx.doi.org/10.1063/1.3683541 (4 pages) | Cited 12 times

Online Publication Date: 10 February 2012

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We report a study of the quantum dot (QD) emission in short photonic crystal waveguides. We observe that the quantum dot photoluminescence intensity and decay rate are strongly enhanced when the emission energy is in resonance with Fabry-Perot (FP) cavity modes in the slow-light regime of the dispersion curve. The experimental results are in agreement with previous theoretical predictions and are further supported by three-dimensional finite element simulations. Our results show that the combination of slow group velocity and Fabry-Perot cavity resonance provide an avenue to efficiently channel photons from quantum dots into waveguides for integrated quantum photonic applications.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.-m Photoluminescence, properties and materials
02.70.Dh Finite-element and Galerkin methods

Periodically focused modes in chains of dielectric spheres

Arash Darafsheh and Vasily N. Astratov

Appl. Phys. Lett. 100, 061123 (2012); http://dx.doi.org/10.1063/1.3684246 (4 pages) | Cited 2 times

Online Publication Date: 10 February 2012

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We show that, theoretically, Brewster angle conditions for transverse magnetic polarized rays can be periodically reproduced in chains of spheres with index n = math giving rise to lossless periodically focused modes with 2D period, where D is the sphere diameter. Using ray tracing for a spherical emitter with the diameter D we show that chains of spheres work as filters of such modes at 1.72 < n < 1.85. This leads to tapering of the focused beams combined with the reduction of their attenuation along the chain. Experimentally, the “beam tapering” effect was observed in chains of 300 μm sapphire spheres with index ∼1.77 in visible.
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42.79.Gn Optical waveguides and couplers
78.20.Bh Theory, models, and numerical simulation
42.15.Dp Wave fronts and ray tracing
42.70.-a Optical materials

Mechanically compliant grating reflectors for optomechanics

Utku Kemiktarak, Michael Metcalfe, Mathieu Durand, and John Lawall

Appl. Phys. Lett. 100, 061124 (2012); http://dx.doi.org/10.1063/1.3684248 (3 pages) | Cited 2 times

Online Publication Date: 10 February 2012

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We demonstrate micromechanical reflectors with a reflectivity as large as 99.4% and a mechanical quality factor Q as large as 7.8 × 105 for optomechanical applications. The reflectors are silicon nitride membranes patterned with sub-wavelength grating structures, obviating the need for the many dielectric layers used in conventional mirrors. We have employed the reflectors in the construction of a Fabry-Perot cavity with a finesse as high as F = 1200, and used the optical response to probe the mechanical properties of the membrane.
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42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings

Directional waveguide coupling from a wavelength-scale deformed microdisk laser

Brandon Redding, Li Ge, Glenn S. Solomon, and Hui Cao

Appl. Phys. Lett. 100, 061125 (2012); http://dx.doi.org/10.1063/1.3684249 (3 pages) | Cited 1 time

Online Publication Date: 10 February 2012

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We demonstrate uni-directional evanescent coupling of lasing emission from a wavelength-scale deformed microdisk to a waveguide. This is attributed to the Goos-Hänchen shift and Fresnel filtering effect that result in a spatial separation of the clockwise (CW) and counter-clockwise (CCW) propagating ray orbits. By placing the waveguide tangentially at different locations to the cavity boundary, we may selectively couple the CW (CCW) wave out, leaving the CCW (CW) wave inside the cavity, which also reduces the spatial hole burning effect. The device geometry is optimized with a full-wave simulation tool, and the lasing behavior and directional coupling are confirmed experimentally.
Show PACS
42.55.Sa Microcavity and microdisk lasers
42.79.Ci Filters, zone plates, and polarizers
42.15.-i Geometrical optics
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