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30 May 2005

Volume 86, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 86, 223902 (2005); http://dx.doi.org/10.1063/1.1938253 (3 pages)

Philip J. Lee, Paul J. Hung, Robin Shaw, Lily Jan, and Luke P. Lee
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GaN-based light-emitting diodes with indium tin oxide texturing window layers using natural lithography

R. H. Horng, C. C. Yang, J. Y. Wu, S. H. Huang, C. E. Lee, and D. S. Wuu

Appl. Phys. Lett. 86, 221101 (2005); http://dx.doi.org/10.1063/1.1940723 (3 pages) | Cited 57 times

Online Publication Date: 24 May 2005

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There is a significant gap between the internal and external efficiencies of conventional GaN light-emitting diodes (LEDs). The reason for this shortfall is the narrow escape cone for light in high refractive index semiconductors. In this letter, the p-side-up GaN/sapphire LEDs with surface textured indium tin oxide (ITO) widow layers were investigated using natural lithography with polystyrene spheres as the etching mask. Under optimum etching conditions, the surface roughness of the ITO film can reach 140 nm while the polystyrene sphere on the textured ITO surface is maintained at about 250–300 nm in diameter. The output power of the ITO/GaN LED with and without surface texturing is 10.9, and 8.5 mW at 20 mA, respectively. The LEDs fabricated using the surface-textured ITO produced an output power that exceeded that of the planar-surface LED by about 28% at 20 mA.
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85.60.Jb Light-emitting devices
81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning

Amplified spontaneous emission in an organic semiconductor multilayer waveguide structure including a highly conductive transparent electrode

M. Reufer, J. Feldmann, P. Rudati, A. Ruhl, D. Müller, K. Meerholz, C. Karnutsch, M. Gerken, and U. Lemmer

Appl. Phys. Lett. 86, 221102 (2005); http://dx.doi.org/10.1063/1.1938001 (3 pages) | Cited 19 times

Online Publication Date: 24 May 2005

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We demonstrate that the amplified spontaneous emission (ASE) threshold in multilayer waveguide structures suitable for the use in future organic injection lasers can be drastically reduced by inserting a crosslinked hole transport layer (HTL) between a highly conductive indium tin oxide (ITO) electrode and the polymer emission layer. While no ASE is observed when the active layer material is directly spincoated onto the ITO electrode, it can be completely restored upon insertion of a 300-nm-thick HTL. This observation is attributed to reduced attenuation of the waveguided mode enabling the ASE process and is theoretically confirmed by calculations of the mode intensity fraction propagating in the absorptive ITO electrode.
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68.65.Ac Multilayers
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.45.+h Stimulated emission
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Stability of phase-modulated quantum key distribution systems

Zheng-Fu Han, Xiao-Fan Mo, You-Zhen Gui, and Guang-Can Guo

Appl. Phys. Lett. 86, 221103 (2005); http://dx.doi.org/10.1063/1.1931824 (3 pages) | Cited 11 times

Online Publication Date: 24 May 2005

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The stability of double Mach–Zehnder implementation has been investigated in experiment, which is important for practical quantum key distribution systems. The results of experiment show that the random fluctuation of interference visibility comes from polarization disturbance, especially from that of transmission fiber. A theoretical model is built and a necessary condition is given for intrinsic-stabilization unidirectional quantum key distribution system.
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03.67.Dd Quantum cryptography and communication security
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Integrated chirp compensation in a monolithic passively mode-locked semiconductor diode laser

Michael B. Flynn, Liam O’Faolain, and Thomas F. Krauss

Appl. Phys. Lett. 86, 221104 (2005); http://dx.doi.org/10.1063/1.1940728 (2 pages) | Cited 3 times

Online Publication Date: 25 May 2005

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We present traveling wave numerical simulations of passively mode-locked diode lasers that incorporate chirp compensation monolithically using a Fabry–Pérot interferometer, which provides a negative group delay. Numerical results show pulse compression of up to 65%. Time-frequency domain study of the pulses reveal a significant reduction in chirp across the pulse. Limitations of this simple linear chirp compensation scheme are examined.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
85.60.Bt Optoelectronic device characterization, design, and modeling
07.60.Ly Interferometers

Mask-free photolithographic exposure using a matrix-addressable micropixellated AlInGaN ultraviolet light-emitting diode

C. W. Jeon, E. Gu, and M. D. Dawson

Appl. Phys. Lett. 86, 221105 (2005); http://dx.doi.org/10.1063/1.1942636 (3 pages) | Cited 20 times

Online Publication Date: 25 May 2005

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We report the integration of a UV-curable polymer microlens array onto a matrix-addressable, 368-nm-wavelength, light-emitting diode device containing 64×64 micropixel elements. The geometrical and optical parameters of the microlenses were carefully chosen to allow the highly divergent emission from each micropixel to be collimated into a narrow beam of about 8-μm diam, over a distance of more than 500 μm. This device is demonstrated as a photolithographic exposure tool, where the pattern-programmable array plays the role both of light source and photomask. A simple pattern comprised of two disks having 16-μm diam and 30-μm spacing was transferred into an i-line photoresist.
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85.60.Jb Light-emitting devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.65.Cf Surface cleaning, etching, patterning
42.79.Bh Lenses, prisms and mirrors
42.70.Jk Polymers and organics
42.72.Bj Visible and ultraviolet sources

Microfabricated SrTiO3 ridge waveguides

M. Gaidi, L. Stafford, J. Margot, M. Chaker, R. Morandotti, and M. Kulishov

Appl. Phys. Lett. 86, 221106 (2005); http://dx.doi.org/10.1063/1.1942634 (3 pages) | Cited 5 times

Online Publication Date: 26 May 2005

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We report the microfabrication and characterization of SrTiO3/SiO2/Si ridge waveguides. SrTiO3 films are very attractive for optical integrated systems as they present a high transparency in the visible and infrared wavelength range as well as a relatively high refractive index. In this work, SrTiO3 films were grown by means of a reactive pulsed-laser-deposition technique and patterned using UV photolithography and high-density plasma etching. Propagation and loss characteristics at the telecommunication wavelength of 1.55 μm were investigated using top-view scattering and Fabry-Perot resonance methods. For specific ridge widths, we obtained single-mode propagation with relatively low losses ( ∼ 1.5 dB/cm), thereby demonstrating the strong potential of SrTiO3 films for guided-wave components for advanced optical integrated systems.
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42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Wc Optical coatings
81.15.Fg Pulsed laser ablation deposition
85.40.Hp Lithography, masks and pattern transfer

Transmission terahertz waveguide-based imaging below the diffraction limit

M. M. Awad and R. A. Cheville

Appl. Phys. Lett. 86, 221107 (2005); http://dx.doi.org/10.1063/1.1942637 (3 pages) | Cited 24 times

Online Publication Date: 26 May 2005

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Using a terahertz line source from a near dispersion-free parallel plate waveguide, we demonstrate broad bandwidth imaging at terahertz frequencies with subwavelength image resolution. Terahertz radiation is coupled into a parallel plate waveguide with a 100 μm plate spacing, which serves as the imaging aperture. The image data are collected as projections and the final image is reconstructed using the filtered back-projection algorithm, similar to that in x-ray computed tomography. Images taken using a waveguide-based line source demonstrate higher resolution than can be achieved using a confocal cylindrical lens setup.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.79.Gn Optical waveguides and couplers
42.30.Wb Image reconstruction; tomography

Reverse-bias electroluminescence imaging to diagnose failures of vertical-cavity surface-emitting lasers

D. K. McElfresh and D. Vacar

Appl. Phys. Lett. 86, 221108 (2005); http://dx.doi.org/10.1063/1.1943496 (3 pages) | Cited 2 times

Online Publication Date: 27 May 2005

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The charge flowing through the junction of vertical-cavity surface-emitting lasers (VCSELs) under reverse-bias gives rise to electroluminescence (EL) when breakdown conditions are satisfied. We collected the reverse-bias EL of VCSEL devices that had been subjected to accelerated stress. We observed distinctly different spatial distributions of the reverse-bias EL: for survivor (nondegraded) devices the breakdown current appears to be confined to one well-defined filament while for dark (degraded) VCSELs the reverse-bias EL pattern is a disordered network of filaments. We show that the line dislocation network that renders the VCSELs dark is directly imaged as the spatial distribution of the reverse-bias EL.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Phospho-tellurite glasses containing heavy metal oxides for ultrabroad band fiber Raman amplifiers

G. Senthil Murugan, Takenobu Suzuki, and Yasutake Ohishi

Appl. Phys. Lett. 86, 221109 (2005); http://dx.doi.org/10.1063/1.1944225 (3 pages) | Cited 11 times

Online Publication Date: 27 May 2005

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Multicomponent phospho-tellurite glasses containing heavy metal oxides and alkaline earth oxides have been fabricated. These glasses have thermal stabilities as high as 224 °C, which make them suitable for various fiber devices applications. The Raman intensities and cross sections of these glasses are compared relative to silica. These glasses show superior relative Raman cross sections than silica and conventional tellurite glasses. The presence of heavy metal oxides and alkaline earth oxides makes the Raman bands due to TeO2 and P2O5 continuous and one such glass has continuous Raman bandwidths exceeding 700 cm−1. Thus, these glasses could be potential candidates for ultrawide band fiber Raman amplifiers.
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42.70.Ce Glasses, quartz
81.05.Kf Glasses (including metallic glasses)
78.30.Hv Other nonmetallic inorganics
42.55.Wd Fiber lasers
42.55.Ye Raman lasers
42.60.By Design of specific laser systems
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Tunable electrochromic photonic crystals

Su-Lan Kuai, Georges Bader, and P. V. Ashrit

Appl. Phys. Lett. 86, 221110 (2005); http://dx.doi.org/10.1063/1.1929079 (3 pages) | Cited 34 times

Online Publication Date: 27 May 2005

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Photonic crystals based on the electrochromic phenomenon have been fabricated and proposed for band gap tuning. Electrochromic tungsten trioxide (WO3) inverse opals have been fabricated by polystyrene colloidal crystal templating. The WO3 matrix was obtained through a dip-infiltrating sol-gel process, with subsequent removal of the polymer microspheres by calcination. Scanning electron micrographs confirm the ordering of the hexagonal macroporous structure. The reflection spectra show two pronounced Bragg diffraction peaks. By inserting lithium into the crystals, the first reflection peak shifts gradually toward shorter wavelength for 36 nm, while the second reflection peak shifts toward longer wavelength for about 28 nm. This should be of great interest for photonic device applications.
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42.70.Qs Photonic bandgap materials
81.40.Gh Other heat and thermomechanical treatments
42.86.+b Optical workshop techniques
61.43.Gt Powders, porous materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Thermo-optic photonic crystal light modulator

Mark T. Tinker and Jeong-Bong Lee

Appl. Phys. Lett. 86, 221111 (2005); http://dx.doi.org/10.1063/1.1944212 (3 pages) | Cited 11 times

Online Publication Date: 27 May 2005

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A device concept is proposed for modulating light in silicon-based photonic crystal devices by using highly localized high-temperature modulation of a compact device to vary the position of the cutoff frequency in a photonic crystal waveguide and modulate light. The position of the cutoff frequency can be varied by up to 60 nm at the telecommunication wavelength of 1550 nm by locally increasing the temperature of the device. Modulators of a few to several micrometers in width can be designed that can modulate light with extinction ratios up to 50 dB and low insertion loss.
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42.79.Hp Optical processors, correlators, and modulators
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
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