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6 Nov 2006

Volume 89, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 192506 (2006); http://dx.doi.org/10.1063/1.2385405 (3 pages)

M. V. Costache, M. Sladkov, C. H. van der Wal, and B. J. van Wees
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Jitter reduction of two synchronized picosecond mode-locked lasers using balanced cross-correlator with two-photon detectors

Takeo Minamikawa, Naoki Tanimoto, Mamoru Hashimoto, Tsutomu Araki, Minoru Kobayashi, Katsumasa Fujita, and Satoshi Kawata

Appl. Phys. Lett. 89, 191101 (2006); http://dx.doi.org/10.1063/1.2374803 (3 pages) | Cited 10 times

Online Publication Date: 6 November 2006

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The authors have developed a highly synchronized picosecond mode-locked laser system. A balanced cross-correlator using two-photon detectors was employed to observe femtosecond order timing jitter between two picosecond lasers (1.26 fs with 150 Hz bandwidth and 7.14 fs with 1 kHz bandwidth), and a signal from the correlator was used as a feedback control signal to reduce the timing jitter. The timing jitter between the two lasers was reduced to 8 fs through a low-pass filter with 150 Hz bandwidth.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
85.60.Gz Photodetectors (including infrared and CCD detectors)

Channel waveguide array in Ce-doped potassium sodium strontium barium niobate crystal fabricated by He+ ion implantation

Feng Chen, Lei Wang, Xue-Lin Wang, Ke-Ming Wang, and Qing-Ming Lu

Appl. Phys. Lett. 89, 191102 (2006); http://dx.doi.org/10.1063/1.2374848 (3 pages) | Cited 3 times

Online Publication Date: 6 November 2006

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The authors report on the fabrication of one dimensional channel waveguide array in photorefractive Ce-doped potassium sodium strontium barium niobate crystal by photographic masking and following direct multiple energy He+ ion implantation. The dark mode spectroscopy is investigated for determining the refractive index modulation of the waveguide. The Floquet-Bloch modes (band transmission spectra) of the light propagating in the array are observed. It is found that the induced optical barriers with reduced refractive indices form semiclosed wedged walls, which confine the enclosed region (together with air) to be channel waveguides. The propagation loss of the waveguide array is determined to be ∼ 1.6 dB/cm for ordinary polarized light at 632.8 nm.
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42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Gn Optical waveguides and couplers

Stable electroluminescence of nanocrystalline silicon device activated by high pressure water vapor annealing

B. Gelloz, T. Shibata, and N. Koshida

Appl. Phys. Lett. 89, 191103 (2006); http://dx.doi.org/10.1063/1.2385206 (3 pages) | Cited 16 times

Online Publication Date: 6 November 2006

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Electroluminescence (EL) and electrical properties of nanocrystalline porous silicon (PS) diodes have been sufficiently improved by introducing high pressure water vapor annealing into the active PS layer. The EL emission is significantly enhanced without affecting the operating voltage. In addition, the fabricated device shows no degradations in both the EL intensity and the diode current density under a dc operation. The EL spectra coincide well with the photoluminescence ones. The obtained high EL performance is presumably caused by complete passivation of nanocrystalline silicon surfaces by thin tunnel oxides with mostly unstrained uniform network and little interfacial trapping defects.
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85.60.Jb Light-emitting devices

Growth of InAlAs self-assembled quantum dots on InAlGaAs/InP for 1.55 μm laser applications by metalorganic chemical vapor deposition

X. B. Zhang, J. H. Ryou, and R. D. Dupuis

Appl. Phys. Lett. 89, 191104 (2006); http://dx.doi.org/10.1063/1.2385693 (3 pages) | Cited 1 time

Online Publication Date: 7 November 2006

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We report on the growth of InAlAs self-assembled quantum dots or simply (QDs) on In0.53(Al0.5Ga0.5)0.47As matrices lattice matched on InP (001) substrates using metal organic chemical vapor deposition. We found that (1) a small amount of aluminum strongly affects the morphology of the InAlAs QDs, (2) using a long growth interruption ( ∼ 140–190 s) before the growth of the QDs is an important element in QD formation, and (3) the AsH3 flow rate during the growth of QDs are very important to get high-quality and high-density QDs on the InAlGaAs surface. A bimodal size distribution of InAlAs QDs is found at low growth temperatures. However, when raising the QD growth temperature, the density of “big” InAlAs QDs becomes lower while the density of “small” QDs becomes much higher. Eventually, a high-density ( ∼ 5.1×1010 cm−2) unimodal size distribution of In0.92Al0.08As QDs with emission around λ ∼ 1.55 μm is realized at the optimized growth temperature condition. The QDs and the In0.53(Al0.5Ga0.5)0.47As barrier are grown at the same temperature of 650 °C.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Dn Self-assembly
42.62.-b Laser applications

Broadband femtosecond frequency doubling in random media

R. Fischer, S. M. Saltiel, D. N. Neshev, W. Krolikowski, and Yu. S. Kivshar

Appl. Phys. Lett. 89, 191105 (2006); http://dx.doi.org/10.1063/1.2374678 (3 pages) | Cited 49 times

Online Publication Date: 7 November 2006

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The authors demonstrate broadband femtosecond phase-matched noncollinear second-harmonic generation (SHG) in strontium barium niobate crystals with random ferroelectric domains. The process is similar to femtosecond SHG in ultrathin crystals, but it results in higher efficiency and exact mapping of the spectrum of the fundamental field into the spectrum of the second harmonics, even for pulses with complex spectral profiles. The observed parametric conversion process can be used as an efficient frequency mapping from infrared to visible for the femtosecond pulse monitoring.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Mp Nonlinear optical crystals
77.80.Dj Domain structure; hysteresis

Integrated multiplexed biosensors based on liquid core optical ring resonators and antiresonant reflecting optical waveguides

Ian M. White, Hesam Oveys, Xudong Fan, Terry L. Smith, and Junying Zhang

Appl. Phys. Lett. 89, 191106 (2006); http://dx.doi.org/10.1063/1.2387112 (3 pages) | Cited 33 times

Online Publication Date: 7 November 2006

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The authors demonstrate integrated biosensors utilizing antiresonant reflecting optical waveguides (ARROWs) to excite the whispering gallery modes of a liquid core optical ring resonator (LCORR) sensor. Because this architecture is based on integration, it is robust and well suited for dense multiplexing of sensors. They analytically and experimentally characterize the coupling between the ARROW structure and the LCORR and show good agreement between the coupling theory and experimental results. The multiplexing capability is experimentally demonstrated by exciting multiple ring resonators along a single LCORR using the ARROW array. Also, they show the label-free detection of bovine serum albumin with this LCORR-ARROW system.
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87.80.-y Biophysical techniques (research methods)
42.79.Gn Optical waveguides and couplers
87.14.E- Proteins
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Growth and fabrication of InGaNP-based yellow-red light emitting diodes

V. A. Odnoblyudov and C. W. Tu

Appl. Phys. Lett. 89, 191107 (2006); http://dx.doi.org/10.1063/1.2374846 (3 pages) | Cited 5 times

Online Publication Date: 7 November 2006

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The authors describe the growth and fabrication of InGaNP quantum well (QW)-based yellow-red light emitting diodes (LEDs) grown directly on transparent GaP (100) wafers. The dependence of InyGa1−yN0.005P0.995/GaP conduction and valence band offsets on the In composition was calculated, and the dependence of AlxGa1−xP/GaP band offsets on the Al concentration was also calculated. Using Al0.14Ga0.86P cladding layers increases the light output from a LED chip by 15%. InGaNP/GaP multiple QW LED structures show an increase of light output and saturation current.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Efficient single-photon counting at 1.55 μm by intracavity frequency upconversion in a unidirectional ring laser

Haifeng Pan, Huafang Dong, Heping Zeng, and Wei Lu

Appl. Phys. Lett. 89, 191108 (2006); http://dx.doi.org/10.1063/1.2378588 (3 pages) | Cited 10 times

Online Publication Date: 7 November 2006

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A single-photon signal at 1.55 μm was converted to its visible replica by sum-frequency mixing with a strong intracavity pump of a unidirectional ring laser at 1.06 μm in a periodically poled lithium niobate (PPLN) crystal. In the ring laser configuration, standing-wave photorefractive effects in the PPLN crystal could be suppressed and consequently, the spectral bandwidth of the intracavity pump could be controlled for excellent quasi-phase-matching. A conversion efficiency of 96% was demonstrated, and the corresponding background counts were less than 6.0×105 s−1. The single-photon upconversion was used for efficient single-photon counting at 1.55 μm with long-term stability.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.50.Ar Photon statistics and coherence theory
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Photo-cross-linkable light-emitting polymers for holographic patterning

Lijun Wu, Woody Y. Y. Tong, Yongchun Zhong, Kam Sing Wong, Jianli Hua, Matthias Häußler, Jacky W. Y. Lam, and Ben Zhong Tang

Appl. Phys. Lett. 89, 191109 (2006); http://dx.doi.org/10.1063/1.2384967 (3 pages) | Cited 2 times

Online Publication Date: 7 November 2006

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Blue light-emitting poly(1-phenyl-1-alkyne)s containing photo-cross-linkable vinyl pendants were synthesized and photophysically characterized. Photoluminescence quantum yields are virtually unchanged for pristine and photo-cross-linked films, showing excellent stability and light-emitting property of the insoluble polymer film after photo-cross-linking process. By using laser interference lithography technique, active submicron two-dimensional photonic crystal structures have been fabricated by exposure to UV light. The obtained high quality nanostructures demonstrate that these polymers are applicable in active photonic devices such as distributed feedback laser. Furthermore, the achievable resolution of these polymers is ∼ 50 nm, implying that these polymers may find potential applications in active nanodevices.
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42.70.Jk Polymers and organics
42.40.My Applications
81.16.Nd Micro- and nanolithography
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds

Silicon-based injection lasers using electronic intersubband transitions in the L valleys

Kristina Driscoll and Roberto Paiella

Appl. Phys. Lett. 89, 191110 (2006); http://dx.doi.org/10.1063/1.2385861 (3 pages) | Cited 20 times

Online Publication Date: 8 November 2006

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The authors investigate the use of electronic intersubband transitions in Ge/SiGe quantum wells on SiGe (001) virtual substrates for the development of silicon-based long-wavelength quantum cascade lasers. These heterostructures can provide relatively strong quantum confinement in the Ge L valleys particularly if the SiGe layers are sufficiently thin so that L-to-Δ intervalley scattering paths are suppressed. Numerical simulations indicate that low-threshold operation can be obtained from these devices, thanks to the nonpolar nature of SiGe. Furthermore, the tensor properties of the L-valley effective mass are favorable for the development of vertical emitting intersubband lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Polarization-resolved optical absorption in single V-groove quantum wires

S. Palmgren, H. Weman, A. Schoenberg, K. F. Karlsson, M.-A. Dupertuis, K. Leifer, A. Rudra, and E. Kapon

Appl. Phys. Lett. 89, 191111 (2006); http://dx.doi.org/10.1063/1.2386093 (3 pages) | Cited 3 times

Online Publication Date: 8 November 2006

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Optical transitions associated with all three linear polarization directions were investigated in single GaAs V-groove quantum wires of different wire thicknesses. This was accomplished by combining absorption measurements in V-groove waveguide geometry with surface-excited photoluminescence excitation spectroscopy. The observed transitions were identified with the aid of model calculations. It is shown that excitonic intersubband coupling should be accounted for in order to explain the optical transitions associated with confined light-hole-like states. The results are relevant for the design of efficient quantum wire waveguide modulators and lasers.
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78.67.Lt Quantum wires
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.-y Excitons and related phenomena
73.21.Hb Quantum wires

Nitride-based light-emitting diodes with p-AlInGaN surface layers prepared at various temperatures

C. H. Kuo, C. W. Kuo, C. M. Chen, B. J. Pong, and G. C. Chi

Appl. Phys. Lett. 89, 191112 (2006); http://dx.doi.org/10.1063/1.2386914 (3 pages) | Cited 2 times

Online Publication Date: 8 November 2006

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The authors have prepared bulk p-AlInGaN layers and light-emitting diodes (LEDs) with p-AlInGaN surface layers by metal organic chemical vapor deposition. They found that the surfaces of the LEDs with p-AlInGaN layers are rough with high density of hexagonal pits. They also found that the pit width and the pit density depend on the growth temperature of the p-AlInGaN layer. Furthermore, it is found that a 62% enhancement in output intensity can be achieved from the LED with an 820 °C p-AlInGaN cap layer without increasing the LED operation voltage.
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85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Photonic crystal quantum cascade lasers with improved threshold characteristics operating at room temperature

S. Höfling, J. Heinrich, H. Hofmann, M. Kamp, J. P. Reithmaier, A. Forchel, and J. Seufert

Appl. Phys. Lett. 89, 191113 (2006); http://dx.doi.org/10.1063/1.2387115 (3 pages) | Cited 5 times

Online Publication Date: 8 November 2006

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The authors have fabricated GaAs/Al0.45Ga0.55As quantum cascade lasers (QCLs) with two-dimensional photonic crystal (PhC) mirrors. The monolithically integrated PhC mirrors consist of a triangular lattice of ∼ 14 μm deeply etched semiconductor pillars. The PhC is designed to exhibit a photonic band gap for both the ΓM and the ΓK crystal orientation and provides reflectivities of >80%. Compared to a reference laser with the same cavity length of 600 μm but as-cleaved facets, the QCLs with ΓM and ΓK oriented PhCs show reductions of the threshold current by 34% and 30%, respectively.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Bh Lenses, prisms and mirrors

Radiation loss of coupled-resonator waveguides in photonic-crystal slabs

M. L. Povinelli and Shanhui Fan

Appl. Phys. Lett. 89, 191114 (2006); http://dx.doi.org/10.1063/1.2387131 (3 pages) | Cited 12 times

Online Publication Date: 8 November 2006

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The authors characterize the intrinsic radiation loss of coupled-resonator optical waveguides by defining a waveguide-quality factor Q. They find that tuning an isolated resonator in a photonic-crystal slab to maximize its Q can also increase the waveguide Q. Due to interference between different resonators, the waveguide can have far lower loss than the isolated cavity; in other cases it can have far greater loss. They show that the dependence of waveguide Q on wave vector can largely be predicted by the shifting of the light cone within a tight-binding model.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Very short wavelength (λ = 3.1–3.3 μm) quantum cascade lasers

J. Devenson, D. Barate, O. Cathabard, R. Teissier, and A. N. Baranov

Appl. Phys. Lett. 89, 191115 (2006); http://dx.doi.org/10.1063/1.2387473 (3 pages) | Cited 37 times

Online Publication Date: 8 November 2006

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Quantum cascade lasers emitting at wavelengths as short as 3.1–3.3 μm are reported. Such high intersubband emission energies (up to 400 meV) have been obtained thanks to the high conduction band offset of the InAs/AlSb material system. The structures, grown by molecular beam epitaxy on InAs substrates, are based on the bound-to-continuum design and use a low loss plasmon enhanced waveguide consisting of n+-InAs cladding layers with InAs/AlSb superlattice spacers surrounding the active zone. The lasers exhibit threshold current densities close to 3 kA/cm2 at 83 K and operate in pulsed mode up to 240 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Random lasing from dye-gold nanoparticles in polymer films: Enhanced gain at the surface-plasmon-resonance wavelength

O. Popov, A. Zilbershtein, and D. Davidov

Appl. Phys. Lett. 89, 191116 (2006); http://dx.doi.org/10.1063/1.2364857 (3 pages) | Cited 32 times

Online Publication Date: 8 November 2006

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The authors report on gold nanoparticle enhancement of the gain in dyes/nanoparticles/polymer film for random lasers. Importantly, they demonstrate a lower threshold for lasing and a stronger output intensity, which depend on the nanoparticle (NP) size. By calculating the “NP scattering resonance” using Mie theory and the measured surface-plasmon resonance, we can qualitatively explain the results, suggesting that the random lasing properties are dominated by an enhanced photon scattering mechanism induced by the surface plasmons.
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42.55.Zz Random lasers
42.70.Hj Laser materials

Dielectric spectroscopy analysis of CaCu3Ti4O12 polycrystalline systems

P. R. Bueno, M. A. Ramírez, J. A. Varela, and E. Longo

Appl. Phys. Lett. 89, 191117 (2006); http://dx.doi.org/10.1063/1.2386916 (3 pages) | Cited 20 times

Online Publication Date: 9 November 2006

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Dielectric spectroscopy was used in this study to examine CaCu3Ti4O12 polycrystalline samples. The analysis involved systems presenting low non-Ohmic properties, and the grain’s internal domain was evaluated separately from the contribution of barrier-layer capacitances associated with Schottky-type barriers in this type of material. The effect of oxygen-rich atmosphere and high cooling rate was evaluated, revealing a strong increase in the dielectric properties of the CaCu3Ti4O12 system under these conditions. This effect was attributed to a chemical change in the grain’s internal domain, which may be considered an internal barrier-layer capacitance of the polycrystalline material.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
61.72.Mm Grain and twin boundaries
81.40.Gh Other heat and thermomechanical treatments

Temperature dependence of the gain in p-doped and intrinsic 1.3 μm InAs/GaAs quantum dot lasers

N. F. Massé, S. J. Sweeney, I. P. Marko, A. R. Adams, N. Hatori, and M. Sugawara

Appl. Phys. Lett. 89, 191118 (2006); http://dx.doi.org/10.1063/1.2387114 (3 pages) | Cited 13 times

Online Publication Date: 9 November 2006

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The gain of p-doped and intrinsic InAs/GaAs quantum dot lasers is studied at room temperature and at 350 K. Our results show that, although one would theoretically expect a higher gain for a fixed carrier density in p-doped devices, due to the wider nonthermal distribution of carriers amongst the dots at T = 293 K, the peak net gain of the p-doped lasers is actually less at low injection than that of the undoped devices. However, at higher current densities, p doping reduces the effect of gain saturation and therefore allows ground-state lasing in shorter cavities and at higher temperatures.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
61.72.uj III-V and II-VI semiconductors

X-valley leakage in GaAs/AlGaAs quantum cascade lasers

X. Gao, D. Botez, and I. Knezevic

Appl. Phys. Lett. 89, 191119 (2006); http://dx.doi.org/10.1063/1.2387485 (3 pages) | Cited 7 times

Online Publication Date: 9 November 2006

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The authors present a Monte Carlo simulation of GaAs/Al0.33Ga0.67As and GaAs/Al0.45Ga0.55As quantum cascade lasers (QCLs) that incorporates both Γ- and X-valley transport. The dominant X-valley leakage path in both lasers is interstage X→X scattering. The leakage current is much higher in the 33%-Al QCL, as strong coupling of its weakly localized Γ-valley states to the next-stage continuum Γ states (Γc), followed by strong same-stage Γc→X scattering, ensures high X-valley population and subsequent high X→X leakage current at 300 K, even at low fields. Very good agreement with experiment is obtained at both cryogenic and room temperatures.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Enhancement of light extraction from a silicon quantum dot light-emitting diode containing a rugged surface pattern

Kyung-Hyun Kim, Jae-Heon Shin, Nae-Man Park, Chul Huh, Tae-Youb Kim, Kwan-Sik Cho, Jong Cheol Hong, and Gun Yong Sung

Appl. Phys. Lett. 89, 191120 (2006); http://dx.doi.org/10.1063/1.2387862 (3 pages) | Cited 16 times

Online Publication Date: 9 November 2006

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The enhancement in light extraction efficiency from a periodic micron-scale rugged surface pattern on Si quantum dot light-emitting-diode (Si-QD LED) structures was investigated, both numerically and experimentally. Micron-scale rugged surface patterns were fabricated on the top layer of the Si-QD LED to increase the extraction of light from the active layer. The optimum light extraction condition for a Si-QD LED corresponded to a pattern size/period ratio of ∼ 0.7. In experiments, the luminescent powers of a Si-QD LED with/without micron-scale surface patterns increase linearly with current density, and the efficiency of light extraction was enhanced by a factor of 2.8.
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85.60.Jb Light-emitting devices
81.65.Cf Surface cleaning, etching, patterning
81.16.Nd Micro- and nanolithography

Free-space quantum key distribution with Rb vapor filters

Xin Shan, Xianping Sun, Jun Luo, Zheng Tan, and Mingsheng Zhan

Appl. Phys. Lett. 89, 191121 (2006); http://dx.doi.org/10.1063/1.2387867 (3 pages) | Cited 4 times

Online Publication Date: 9 November 2006

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By using Rb vapor filters, free-space quantum key distribution with the B92 protocol was realized experimentally; the filters based on the Faraday anomalous dispersion effect were used to suppress strong background light. With these atomic filters as spectral filtering, average transmission rates of sifted keys and corrected keys have reached as high as 3.14 and 1.56 kbits/s, respectively, while the error rate was maintained at a reasonable low level of 5.10%. The experimental results show that our Rb vapor filters with transmission efficiency of around 60% operate well under the condition of the mean photon number math ⩽ 0.1.
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03.67.Dd Quantum cryptography and communication security
03.67.Hk Quantum communication
42.79.Ci Filters, zone plates, and polarizers

Investigation of Cr- and Al-based metals for the reflector and Ohmic contact on n-GaN in GaN flip-chip light-emitting diodes

Kuang-Po Hsueh, Kuo-Chun Chiang, Yue-Ming Hsin, and Charles J. Wang

Appl. Phys. Lett. 89, 191122 (2006); http://dx.doi.org/10.1063/1.2387888 (3 pages) | Cited 2 times

Online Publication Date: 9 November 2006

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This letter investigates three composite metals used as a reflector and Ohmic contact on n-GaN to simplify the process in a flip-chip light-emitting diode (FCLED). The investigated composite metals were Ti/Al/Ti/Au, Cr/Al/Cr/Au, and Cr/Ti/Au. The specific contact resistivities of the Ti/Al/Ti/Au, Cr/Al/Cr/Au, and Cr/Ti/Au Ohmic contacts on n-GaN were changed from 1.4×10−4, 1.7×10−4, and 1.9×10−4 Ω cm2 to  1.3×10−4, 1.1×10−4, and 3.3×10−5Ω cm2, respectively, after 500 h of thermal stress. The corresponding operating voltages of FCLEDs with different composite metals were changed by less than 1%. After 96 h of thermal stress, the luminous intensities of the three structures decreased by 6.2%, 11.1%, and 1.4%, respectively. The GaN FCLED that was fabricated with Cr/Ti/Au as a reflector and an Ohmic contact on n-GaN exhibits good thermal stability and luminous intensity.
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85.60.Jb Light-emitting devices

Quasi-phase-matched adhered ridge waveguide in LiNbO3

Sunao Kurimura, Yuji Kato, Masayuki Maruyama, Yusuke Usui, and Hirochika Nakajima

Appl. Phys. Lett. 89, 191123 (2006); http://dx.doi.org/10.1063/1.2387940 (3 pages) | Cited 15 times

Online Publication Date: 9 November 2006

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Uniform periodically poled domains were demonstrated in an insulator-sandwiched structure with z-cut lithium niobate wafers for an adhered ridge waveguide. Efficient quasi-phase-matched second harmonic generation was achieved in a mechanically defined ridge waveguide. Strong confinement in the waveguide produced second-harmonic-generation normalized conversion efficiency of 370%/W cm2 in the 1.5 μm wavelength region.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Ultralow threshold on-chip microcavity nanocrystal quantum dot lasers

Bumki Min, Sungjee Kim, Koichi Okamoto, Lan Yang, Axel Scherer, Harry Atwater, and Kerry Vahala

Appl. Phys. Lett. 89, 191124 (2006); http://dx.doi.org/10.1063/1.2387966 (3 pages) | Cited 28 times

Online Publication Date: 9 November 2006

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Chemically synthesized nanocrystal, CdSe/ZnS (core/shell), quantum dots are coated on the surface of an ultrahigh-Q toroidal microcavity and the lasing is observed at room and liquid nitrogen temperature by pulsed excitation of quantum dots, either through tapered fiber or free space. Use of a tapered fiber coupling substantially lowered the threshold energy when compared with the case of free space excitation. The reason for the threshold reduction is attributed to the efficient delivery of pump pulses to the active gain region of the toroidal microcavity. Further threshold reduction was possible by quantum dot surface-coverage control. By decreasing the quantum dot numbers on the surface of the cavity, the threshold energy is further decreased down to 9.9 fJ.
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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
42.81.Qb Fiber waveguides, couplers, and arrays

Microlens array fabrication by laser interference lithography for super-resolution surface nanopatterning

C. S. Lim, M. H. Hong, Y. Lin, Q. Xie, B. S. Luk’yanchuk, A. Senthil Kumar, and M. Rahman

Appl. Phys. Lett. 89, 191125 (2006); http://dx.doi.org/10.1063/1.2374809 (3 pages) | Cited 16 times

Online Publication Date: 10 November 2006

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A technique for large area and fast speed surface nanopatterning of photopolymer surface with laser irradiation through microlens array (MLA) was demonstrated. The laser beam was split into many focused tiny light spots by a 1 μm diameter MLA fabricated by laser interference lithography followed by reflow and reactive ion etching. The fabricated MLA exhibits excellent uniformity and surface quality. Up to 6 250 000 nanopatterns can be fabricated over an area of 5×5 mm2 under KrF excimer laser single pulse exposure. A spot size down to 78 nm was obtained corresponding to super-resolution of λ/3, λ is the incident laser wavelength.
Show PACS
42.86.+b Optical workshop techniques
42.79.Bh Lenses, prisms and mirrors
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
42.62.-b Laser applications
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