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17 Oct 2005

Volume 87, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 87, 161907 (2005); http://dx.doi.org/10.1063/1.2105998 (3 pages)

J. Das, K. B. Kim, F. Baier, W. Löser, and J. Eckert
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Parametric downconversion via cascaded optical nonlinearities in an aperiodically poled MgO:LiNbO3 superlattice

H. C. Guo, Y. Q. Qin, and S. H. Tang

Appl. Phys. Lett. 87, 161101 (2005); http://dx.doi.org/10.1063/1.2099541 (3 pages) | Cited 5 times

Online Publication Date: 10 October 2005

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Quasi-phase-matched parametric downconversion via cascaded optical nonlinearities in an aperiodically poled MgO:LiNbO3 superlattice was studied in theory and experiment. Due to the cascading effect and the abundant reciprocal structure in an aperiodic optical superlattice, multiple-wavelength parametric downconversion in a wide spectrum range can be obtained. Enhancement of the conversion efficiency and output stability through coupling of two nonlinear processes is demonstrated. The result also reveals that the cascaded parametric downconversion process can be used to efficiently downconvert the fundamental wavelength to a longer wavelength of the infrared region. The process can be additionally served as an efficient mechanism to enhance THz wave propagation in a nonlinear optical medium.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Photonic crystal band edge laser array with a holographically generated square-lattice pattern

Chi-O Cho, Jaewook Jeong, Joonhee Lee, Heonsu Jeon, In Kim, Dong Hoon Jang, Yoon Soo Park, and Jong Chun Woo

Appl. Phys. Lett. 87, 161102 (2005); http://dx.doi.org/10.1063/1.2103422 (3 pages) | Cited 16 times

Online Publication Date: 10 October 2005

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We fabricated a photonic band edge laser array based on a two-dimensional square-lattice photonic crystal (PC) slab waveguide using a laser holography (LH) method, instead of the commonly used electron-beam lithography (EBL). The nature of the LH process enabled high-throughput large-area fabrication of band edge lasers. Moreover, the laser performance was comparable to that of reported EBL counterparts. Careful examination of the spectral positions of the observed modes with respect to the calculated photonic band structure identified three main band edge modes as the origins of lasing: M2, X2, and M1. Owing to the gradual change in the air-hole size of the PC, the lasing modes shifted monotonically along the laser array, resulting in an M1 mode span of ∼ 30 nm (centered at 1550 nm) over a distance of 5 mm.
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42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials
42.40.My Applications

Organic solid-state ultraviolet-laser based on spiro-terphenyl

T. Spehr, A. Siebert, T. Fuhrmann-Lieker, J. Salbeck, T. Rabe, T. Riedl, H. H. Johannes, W. Kowalsky, J. Wang, T. Weimann, and P. Hinze

Appl. Phys. Lett. 87, 161103 (2005); http://dx.doi.org/10.1063/1.2105996 (3 pages) | Cited 21 times

Online Publication Date: 11 October 2005

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We report on organic semiconductor lasers based on spiro-terphenyl as active gain medium in a second-order distributed feedback (DFB) structure. In contrast to neat p-terphenyl, the spiro-linked compound forms vitreous amorphous films—an essential prerequisite for low loss laser structures. Spiro-terphenyl shows amplified spontaneous emission in the ultraviolet part of the spectrum at 381 nm. Thin-film lasers with DFB grating periods between 200 and 230 nm exhibit emission wavelengths between 361.9 and 393.8 nm. The minimum threshold energy density under optical pumping is as low as 8.9 μJ/cm2 (383 nm). Therefore, the novel spiro-linked compound paves the way for low-threshold, widely tunable organic semiconductor lasers advancing into the ultraviolet spectral region.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Near-field scanning optical microscopic transient lens for carrier dynamics study in InGaN/GaN

Koichi Okamoto, Axel Scherer, and Yoichi Kawakami

Appl. Phys. Lett. 87, 161104 (2005); http://dx.doi.org/10.1063/1.2105999 (3 pages) | Cited 12 times

Online Publication Date: 11 October 2005

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Time-resolved microscopic transient lens (TR-M-TL) and near-field scanning optical microscopic transient lens (NSOM-TL) were performed to reveal temporal and spatial behavior of carrier dynamics in InGaN/GaN quantum wells. The carrier and thermal dynamics were observed through the time profile of the TR-M-TL signal. Also, NSOM-photoluminescence and NSOM-TL images were observed at the same time. By comparing these two images, both radiative and nonradiative recombination centers in InGaN active layer were unambiguously discriminated with submicrometer scale. Such nonradiative carrier dynamics has been difficult to observe by conventional techniques in spite of its importance.
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07.79.Fc Near-field scanning optical microscopes
42.79.Bh Lenses, prisms and mirrors
78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors
78.67.De Quantum wells
73.21.Fg Quantum wells

Ultrafast control of multiple filamentation by ultrafast laser pulses

Jiansheng Liu, Hartmut Schroeder, See Leang Chin, Ruxin Li, and Zhizhan Xu

Appl. Phys. Lett. 87, 161105 (2005); http://dx.doi.org/10.1063/1.2106022 (3 pages) | Cited 8 times

Online Publication Date: 12 October 2005

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Control of multiple filamentation by laser-induced microlens effect due to a nonlinear interaction of two overlapping laser beams inside a glass plate was demonstrated. Individual or multiple spots on the white light pattern which is a product of multiple filamentation through a mesh can be switched on and off with a very high contrast ratio on a femtosecond time scale. This phenomenon can find applications such as ultrafast optical switch and high-speed sampling.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Bh Lenses, prisms and mirrors
42.65.Pc Optical bistability, multistability, and switching, including local field effects

All-fiber integrated chirped pulse amplification at 1.06 μm using aircore photonic bandgap fiber

R. E. Kennedy and J. R. Taylor

Appl. Phys. Lett. 87, 161106 (2005); http://dx.doi.org/10.1063/1.2112190 (2 pages) | Cited 2 times

Online Publication Date: 12 October 2005

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We demonstrate all-fiber integrated chirped pulse amplification (CPA) at 1.06 μm using an air-core photonic bandgap fiber (APBF). Prior to the CPA stage, 4.0 ps pulses from a modelocked fiber laser were compressed to 1.3 ps in an all fiber integrated pulse compressor based on spectral broadening in a holey fiber and compression in a 12.4 m length of APBF. The compressed 1.3 ps pulses were then stretched to ∼ 20 ps in 125 m of single mode fiber, amplified in a large mode area YDFA and recompressed to 600 fs in 50 m of APBF, which was directly spliced to the amplifier output fiber. The 600 fs output pulses had an estimated peak power of 2.6 kW.
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42.81.Wg Other fiber-optical devices
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Qs Photonic bandgap materials
42.55.Wd Fiber lasers
42.82.Gw Other integrated-optical elements and systems

Near-infrared transparent electrodes for precision Teng–Man electro-optic measurements: In2O3 thin-film electrodes with tunable near-infrared transparency

Lian Wang, Yu Yang, Tobin J. Marks, Zhifu Liu, and Seng-Tiong Ho

Appl. Phys. Lett. 87, 161107 (2005); http://dx.doi.org/10.1063/1.2089184 (3 pages) | Cited 8 times

Online Publication Date: 13 October 2005

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Highly near-infrared (NIR) transparent In2O3 thin films have been grown by ion-assisted deposition at room temperature, and the optical and electrical properties characterized. NIR transparency and the plasma edge frequency can be engineered by control of the film deposition conditions. As-deposited In2O3 thin films were employed as transparent electrodes for direct thin film electro-optic (EO) characterization measurements via the Teng–Man technique. Using LiNbO3 as the standard, the relationship between electrode NIR transparency and Teng–Man EO measurement accuracy was evaluated. It is found that In2O3 electrodes can be tailored to be highly NIR transparent, thus providing far more accurate Teng–Man EO coefficient quantification than tin-doped indium oxide. In addition, the EO coefficients of stilbazolium-based self-assembled superlattice thin films were directly determined for the first time using an optimized In2O3 electrode. EO coefficients r33 of 42.2, 13.1, and 6.4 pm/V are obtained at 633, 1064, and 1310 nm, respectively.
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78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

High-power single-mode vertical-cavity surface-emitting lasers

N. Samal, S. R. Johnson, D. Ding, A. K. Samal, S.-Q. Yu, and Y.-H. Zhang

Appl. Phys. Lett. 87, 161108 (2005); http://dx.doi.org/10.1063/1.2112204 (3 pages) | Cited 2 times

Online Publication Date: 13 October 2005

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This letter reports a design for high-power single-mode operation in vertical-cavity surface-emitting lasers by means of modal gain control using two different sized current apertures to shape the injection-current profile. A smaller current aperture is located several mirror-pairs away from the active region in the p-mirror and a larger current aperture is located in the first n-mirror-pair next to the active region. Both theoretical modeling and experimental test results show substantial improvement in the optical mode behavior using this approach when compared to a traditional single-aperture design. A clear trend of the spectral purity in the modal behavior under continuous wave and pulsed conditions is demonstrated and is in good agreement with theoretical predictions. The best design tested demonstrated a room-temperature continuous wave power output of 7.5 mW with a side mode suppression ratio of 20 dB.
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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
42.79.Bh Lenses, prisms and mirrors

Great improvement of phase controlling of the entirely independent stimulated Brillouin scattering phase conjugate mirrors by balancing the pump energies

Seong Ku Lee, Hong Jin Kong, and Masahiro Nakatsuka

Appl. Phys. Lett. 87, 161109 (2005); http://dx.doi.org/10.1063/1.2115080 (3 pages) | Cited 14 times

Online Publication Date: 13 October 2005

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For developing a beam combination laser with the stimulated Brillouin scattering-phase conjugate mirrors (SBS-PCMs), the phase control of the backward SBS waves is essentially required. We proposed a new effective and practical technique in previous works, in which entirely independent SBS-PCMs are used, so that there is no limit of the number of the beams for the beam combination laser. In this letter, we show that in the proposed technique, the phase of the SBS wave significantly depends on the pump energy and it can be stabilized—although the independently separate SBS-PCMs are used—provided that the pump energies are balanced under the density modulation. In this experimental work, the standard deviation of the relative phase difference between the SBS waves has been reduced less than λ/30 by the amplitude dividing method to provide the pump beams with the nearly same energies.
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42.65.Es Stimulated Brillouin and Rayleigh scattering
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Bh Lenses, prisms and mirrors

Long-band emission of microsphere lasers based on erbium-doped sol-gel silica-alumina glasses

Pham Van Hoi, Chu Thi Thu Ha, and Hoang Quang Hung

Appl. Phys. Lett. 87, 161110 (2005); http://dx.doi.org/10.1063/1.2089186 (3 pages) | Cited 7 times

Online Publication Date: 14 October 2005

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This letter reports on long-band (L band) lasing whispering-gallery modes (WGMs) in microspheres based on sol-gel silica-alumina glasses doped with high concentration of erbium ions (Er+3 from 1250 to 15 000 ppm). The sol-gel method for making these Er-doped silica-alumina glasses is described. The microspheres with diameters from 40 to 200 μm were built by electrical arc. The experimental results show that laser oscillations with high gain at L band were obtained with different coupling schemes, especially with forward pumping and/or backward pumping coupling. The collected laser output power of one WGM could reach to −5 dBm in the L band of 1570–1610 nm.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Ultraviolet-replicated focusing grating coupler in polymers at a wavelength of 405 nm

Dongwoo Suh, Hojun Ryu, Yongwoo Park, and Mun Cheol Paek

Appl. Phys. Lett. 87, 161111 (2005); http://dx.doi.org/10.1063/1.2106025 (3 pages) | Cited 5 times

Online Publication Date: 14 October 2005

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A focusing grating coupler (FGC) in a polymer for a wavelength of 405 nm was implemented on a slab waveguide using nanoscale ultraviolet (UV) replication process. The polymer FGC with a high numerical aperture of 0.85 was designed by Bloch wave theory with the minimum spacing between adjacent grating ridges of 85 nm and replicated from the master pattern. After UV irradiation at an energy density of 2.68 J/cm2 and a loading force of 1 kN for 2 min, the replicated polymer FGC produced a spot size of 347 nm on the focal plane measured at the full width at half maximum. The out-coupling efficiency of the grating is 34%.
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42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings
42.70.Jk Polymers and organics
42.86.+b Optical workshop techniques
42.15.Eq Optical system design

Liquid crystal phase gratings using photoregulated photocrosslinkable polymer liquid crystals

Tomoyuki Sasaki, Hiroshi Ono, Nobuhiro Kawatsuki, and Masaomi Kuwabara

Appl. Phys. Lett. 87, 161112 (2005); http://dx.doi.org/10.1063/1.2106007 (3 pages) | Cited 13 times

Online Publication Date: 14 October 2005

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We have presented liquid crystal phase gratings using photoregulated photocrosslinkable polymer liquid crystals. The phase grating consists of homogeneous and 90°-twisted nematic area and shows unique polarization conversion in the diffraction process. The diffraction properties are well explained by the theory based on Jones calculus.
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42.79.Kr Display devices, liquid-crystal devices
42.79.Dj Gratings
42.70.Df Liquid crystals
61.30.Vx Polymer liquid crystals

Photonic crystal waveguides with acute bending angles

Natalia Malkova and C. Z. Ning

Appl. Phys. Lett. 87, 161113 (2005); http://dx.doi.org/10.1063/1.2105994 (3 pages) | Cited 5 times

Online Publication Date: 14 October 2005

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We propose and study photonic crystal waveguides with bending angles smaller than 90°. The waveguide is formed by coupled defect cavities. To achieve a reflectionless transmission through an acute angle, we surround the defects in the bends with distorted cells having a prescribed symmetry. Detailed analysis and numerical simulation confirm that the transmission through the acute bend can be increased by two orders of magnitude to 100%.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.82.Et Waveguides, couplers, and arrays
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