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2 Oct 2006

Volume 89, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 142101 (2006); http://dx.doi.org/10.1063/1.2358202 (3 pages)

H. C. Lin, P. D. Ye, Y. Xuan, G. Lu, A. Facchetti, and T. J. Marks
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Twin defect modes in one-dimensional photonic crystals with a single-negative material defect

Y. H. Chen, J. W. Dong, and H. Z. Wang

Appl. Phys. Lett. 89, 141101 (2006); http://dx.doi.org/10.1063/1.2357600 (3 pages) | Cited 23 times

Online Publication Date: 2 October 2006

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Twin defect modes are found in one-dimensional photonic crystals stacking with single- negative-permittivity and single-negative-permeability media layers and a single-negative defect. The frequency interval of the two defect modes can be changed by varying the thickness of the defect layer or the thickness ratio of the two stacking layers. Conditions for the emergence of such twin defect modes only relate to the phase thicknesses of the defect layer and the two stacking layers. In addition, the electric fields at the frequencies of the defect modes are strongly localized at the interfaces between the defect layer and its adjacent layers.
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42.70.Qs Photonic bandgap materials
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Focused-ion-beam fabricated vertical fiber couplers on silicon-on-insulator waveguides

Jonathan Schrauwen, Dries Van Thourhout, and Roel Baets

Appl. Phys. Lett. 89, 141102 (2006); http://dx.doi.org/10.1063/1.2356311 (3 pages) | Cited 10 times

Online Publication Date: 2 October 2006

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Focused-ion-beam technology is a versatile micro- and nanostructuring tool, in which material is sputtered locally by a finely focused ion beam. But for photonic applications this process has the inherent inconvenience of generating optical losses due to ion induced damage. Process optimization is needed to reduce these losses. In this letter the authors present the focused-ion-beam fabrication of shallow gratings in silicon-on-insulator waveguides for the coupling of light to a vertically positioned fiber. Using Al2O3 as mask and I2 as selective etchant this resulted in a 24% fiber-to-chip coupling efficiency, which is comparable to similar devices fabricated with conventional etching techniques.
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42.82.Et Waveguides, couplers, and arrays
42.81.Qb Fiber waveguides, couplers, and arrays
42.81.Bm Fabrication, cladding, and splicing
42.79.Dj Gratings
81.16.-c Methods of micro- and nanofabrication and processing
85.60.-q Optoelectronic devices

“Needle beam:” Beyond-diffraction-limit concentration of field and transmitted power in dielectric waveguide

Victor Bondarenko and Yang Zhao

Appl. Phys. Lett. 89, 141103 (2006); http://dx.doi.org/10.1063/1.2358310 (3 pages) | Cited 5 times

Online Publication Date: 2 October 2006

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The authors report the “needle beam,” which is an eigenmode of J0-Y0-K0 profile propagating in a purely dielectric three-medium coaxial cylindrical waveguide, whose field and transmitted power are concentrated within the central medium of diameter beyond the diffraction limit. The huge concentration can be achieved for the TE0m and TM0m eigenmodes within a cylindrical hole of nanometer-scale diameter along the waveguide axis. A difference between refractive indices in the hole and neighbor media can considerably enhance the field and the power transmission along the hole.
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42.79.Gn Optical waveguides and couplers
02.10.Ud Linear algebra

Electro-optic coefficients of Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice measured by polarization-maintaining fiber-optic Mach-Zehnder interferometer

L. Zhao, X. G. Tu, Y. H. Zuo, S. W. Chen, and Q. M. Wang

Appl. Phys. Lett. 89, 141104 (2006); http://dx.doi.org/10.1063/1.2358319 (3 pages) | Cited 3 times

Online Publication Date: 2 October 2006

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Ten-period 5.5 nm Si0.75Ge0.25/10.3 nm Si/2.5 nm Si0.5Ge0.5 trilayer asymmetric superlattice was prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 °C. The stability of Mach-Zehnder interferometer was improved by utilizing polarization-maintaining fibers. According to the electro-optic responses of the superlattice with the light polarization along [110] and [−110], respectively, both electro-optic coefficients γ13 and γ63 of such asymmetric superlattice were measured. γ13 and γ63 are 2.4×10−11 and 1.3×10−11 cm/V, respectively, with the incident light wavelength at 1.55 μm.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Jq Electro-optical effects
07.60.Ly Interferometers
07.60.Vg Fiber-optic instruments
42.81.Pa Sensors, gyros
42.81.Gs Birefringence, polarization

30-nm-wide aluminum nanowire grid for ultrahigh contrast and transmittance polarizers made by UV-nanoimprint lithography

Jian Jim Wang, Lei Chen, Xiaoming Liu, Paul Sciortino, Feng Liu, Frank Walters, and Xuegong Deng

Appl. Phys. Lett. 89, 141105 (2006); http://dx.doi.org/10.1063/1.2358813 (3 pages) | Cited 34 times

Online Publication Date: 2 October 2006

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Both high contrast and high transmittance are preferred for optical polarizers. To achieve high transmittance for aluminum nanowire-grid polarizers, a narrow linewidth is required. In this letter, aluminum nanowire-grid polarizers with 30-nm-wide linewidth and 200 nm depth were fabricated by UV-nanoimprint lithography, which leads to ultrahigh transmittance. To achieve a high contrast, the authors fabricated the 30-nm-wide aluminum nanowire structures on both sides of the glass wafers. An extremely high contrast up to 10 000:1 was achieved, in the visible range, along with good transmittance of 83%–87% for the double-side aluminum nanowire-grid polarizers.
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42.79.Ci Filters, zone plates, and polarizers
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
42.86.+b Optical workshop techniques

Single-mode submonolayer quantum-dot vertical-cavity surface-emitting lasers with high modulation bandwidth

F. Hopfer, A. Mutig, M. Kuntz, G. Fiol, D. Bimberg, N. N. Ledentsov, V. A. Shchukin, S. S. Mikhrin, D. L. Livshits, I. L. Krestnikov, A. R. Kovsh, N. D. Zakharov, and P. Werner

Appl. Phys. Lett. 89, 141106 (2006); http://dx.doi.org/10.1063/1.2358114 (3 pages) | Cited 28 times

Online Publication Date: 2 October 2006

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Single-mode vertical-cavity surface-emitting lasers based on dense arrays of stacked submonolayer grown InGaAs quantum dots, emitting near 980 nm, demonstrate a modulation bandwidth of 10.5 GHz. A low threshold current of 170 μA, high differential efficiency of 0.53 W/A, and high modulation current efficiency factor of 14 GHz/math are realized from a 1 μm oxide aperture single-mode device with a side mode suppression ratio of >40 dB and peak output power of >1 mW. The lasers are also suitable for high temperature operation.
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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
42.60.Fc Modulation, tuning, and mode locking

Exciton resonance tuning for the generation of subpicosecond pulses from a mode-locked semiconductor disk laser

Florian Saas, Günter Steinmeyer, Uwe Griebner, Martin Zorn, and Markus Weyers

Appl. Phys. Lett. 89, 141107 (2006); http://dx.doi.org/10.1063/1.2358117 (3 pages) | Cited 5 times

Online Publication Date: 2 October 2006

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The authors investigate the spectral tuning of the exciton resonance of a surface quantum well saturable absorber mirror for the generation of subpicosecond pulses, employing an optically pumped semiconductor disk laser in the 1 μm spectral range. The all-semiconductor laser generates transform-limited pulses as short as 590 fs at a 3 GHz repetition rate and an output power of 30 mW. The pulse duration of the mode-locked laser was supported by the fast relaxation time of the saturable absorber of 1.0 ps.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
71.35.-y Excitons and related phenomena
42.79.Bh Lenses, prisms and mirrors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Composite-microlens-array-enabled microfluidic sorting

Y. Y. Sun, L. S. Ong, and X.-C. Yuan

Appl. Phys. Lett. 89, 141108 (2006); http://dx.doi.org/10.1063/1.2358306 (3 pages) | Cited 12 times

Online Publication Date: 2 October 2006

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We propose a simple, reliable and cost-effective method for microfluidic sorting of microparticles using an optical potential landscape projected by a composite microlens array (MLA). The MLA enables a high power efficient approach to forming composite shape and size of the projected pattern. Sorting particles by size is demonstrated both theoretically and experimentally.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.79.Bh Lenses, prisms and mirrors
47.85.Np Fluidics

Compound figure of merit for photonic applications of metal nanocomposites

Hernando Garcia, Hare Krishna, and Ramki Kalyanaraman

Appl. Phys. Lett. 89, 141109 (2006); http://dx.doi.org/10.1063/1.2358209 (3 pages) | Cited 2 times

Online Publication Date: 3 October 2006

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Selecting nanocomposites for photonic switching applications requires optimizing their thermal, nonlinear, and two-photon absorption characteristics. The authors simplify this step by defining a compound figure of merit (FOMC) for nanocomposites of noble metals in dielectric based on criteria that limit these structures in photonic applications, i.e., thermal heating and two-photon absorption. The device independent results predict extremely large values of FOMC for a specific combination of the metal and insulator dielectric constants given by ϵh = (ϵ1−ϵ2)/2, where ϵh is the dielectric constant of the host and ϵ1 and ϵ2 are the real and imaginary parts for the metal.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects

Transmission of light by a single subwavelength cylindrical hole in metallic films

Ming Bai and N. García

Appl. Phys. Lett. 89, 141110 (2006); http://dx.doi.org/10.1063/1.2358210 (3 pages) | Cited 3 times

Online Publication Date: 3 October 2006

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This letter presents theory and finite-difference time-domain calculations in excellent agreement with experiments for the transmission of a single subwavelength cylindrical hole in Ag metallic films. The authors discuss the very large enhancement in transmission by single holes in terms of surface plasmons at the interface of the hole. These are similar to the surface plasmons in metallic cylinders reported by Economou and co-workers [ Phys. Rev. B 10, 3038 (1974); 24, 6908 (1981) ]. The peak structures observed in experiments with arrays of holes are a consequence of interference of the beams transmitted by each hole and are determined by the hole periodicities. The role of the arrays in enhancement of the transmission due to surface plasmon polaritons appears to be marginal.
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78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
02.70.Bf Finite-difference methods

Stimulated emission depletion of triplet excitons in a phosphorescent organic laser

M. Reufer, J. M. Lupton, and U. Scherf

Appl. Phys. Lett. 89, 141111 (2006); http://dx.doi.org/10.1063/1.2357023 (3 pages) | Cited 7 times

Online Publication Date: 3 October 2006

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Triplet formation is investigated in an optically pumped polymer laser by detecting the phosphorescence emission after excitation. A clear correlation is observed between the onset of lasing and a saturation of phosphorescence intensity due to stimulated emission depletion of the singlet state and the resulting reduction in intersystem crossing. The results are consistent with intersystem crossing constituting the dominant triplet formation pathway in conjugated polymers. Excitation at different wavelengths has no effect on the triplet saturation behavior, which allows the authors to exclude singlet fission or breaking as the origin of triplet formation. The method constitutes an implementation of a highly nondegenerate excitonic switch.
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42.60.By Design of specific laser systems
42.70.Jk Polymers and organics
42.70.Hj Laser materials
42.55.Px Semiconductor lasers; laser diodes
71.35.-y Excitons and related phenomena

Liquid crystal lens prepared utilizing patterned molecular orientations on cell walls

Mao Ye, Yoshitaka Yokoyama, and Susumu Sato

Appl. Phys. Lett. 89, 141112 (2006); http://dx.doi.org/10.1063/1.2358211 (3 pages) | Cited 12 times

Online Publication Date: 3 October 2006

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A liquid crystal (LC) lens prepared using patterned molecular orientations on cell walls is proposed. On each wall, the LC directors in a circular area are aligned to be parallel, while those outside the area are perpendicular, to the wall. A spatially varying director orientation and a lenslike distribution of refractive index may appear in the LC layer. The LC cell then becomes an optical lens even in the absence of any applied voltages. The focal length of the lens is electrically tunable. The size of the lens prepared in this way can become very small.
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42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
42.79.Bh Lenses, prisms and mirrors
61.30.-v Liquid crystals

Hybrid Fabry-Pérot étalon using an electro-optic polymer for optical modulation

Haiyong Gan, Hongxi Zhang, Christopher T. DeRose, Robert A. Norwood, Mahmoud Fallahi, Jingdong Luo, Alex K.-Y. Jen, Boyang Liu, Seng-Tiong Ho, and Nasser Peyghambarian

Appl. Phys. Lett. 89, 141113 (2006); http://dx.doi.org/10.1063/1.2358298 (3 pages) | Cited 9 times

Online Publication Date: 3 October 2006

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The authors present a Fabry-Pérot étalon using an electro-optic (EO) polymer material as the nonlinear medium. The two electrodes used to apply voltage across the EO polymer include an indium tin oxide electrode outside the étalon cavity and a low-absorption indium oxide electrode inside the étalon cavity. High finesse ( ∼ 234) and a low insertion loss ( ∼ 4 dB) have been obtained. An isolation ratio of 10 dB and ∼ 10% modulation depth at 200 kHz with 5 V applied voltage have been achieved. These results indicate that EO polymer étalons are promising as spatial light modulators for information technology.
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42.79.Hp Optical processors, correlators, and modulators
07.60.Ly Interferometers
42.70.Jk Polymers and organics

Stimulated resonance Raman scattering from polyphenylenevinylene thin film waveguides

Hisao Yanagi, Takatoshi Murai, and Shuhei Fujimoto

Appl. Phys. Lett. 89, 141114 (2006); http://dx.doi.org/10.1063/1.2358850 (3 pages) | Cited 5 times

Online Publication Date: 3 October 2006

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Stimulated resonance Raman scattering (SRRS) from a polymer waveguide has been studied using spin-coated thin films of poly(5-(2-ethylhexyloxy)-2-methoxy-cyanoterephthalydiene). The single SRRS peak with a Raman shift of ∼ 1580 cm−1 was observed above the excitation threshold of ∼ 100 μJ/cm2, overlapping with the amplified spontaneous emission (ASE) band. When the excitation wavelength was varied, the SRRS intensity was maximized at the ASE peak position. It suggests that the light confinement in the polymer waveguide resulting in the stimulated amplification of Raman scattering plays a significant role in the observed SRRS phenomenon. In addition, the thickness dependence of the SRRS gain coefficients suggests some contribution of cooperative interaction to SRRS.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.55.Ye Raman lasers

Excitation wavelength dependence of terahertz emission from InN and InAs

Grace D. Chern, Eric D. Readinger, Hongen Shen, Michael Wraback, Chad S. Gallinat, Gregor Koblmüller, and James S. Speck

Appl. Phys. Lett. 89, 141115 (2006); http://dx.doi.org/10.1063/1.2358938 (3 pages) | Cited 35 times

Online Publication Date: 3 October 2006

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The authors report on the excitation wavelength dependence of terahertz emission from n-InN and bulk p-InAs pumped with femtosecond pulses tunable from 800 to 1500 nm. The terahertz amplitude, normalized to pump and probe power, from both narrow band gap semiconductors remains relatively constant over the excitation wavelength range. In addition, terahertz radiation from In- and N-face InN samples with bulk carrier concentrations ranging from 1017 to 1019 cm−3 is also investigated, showing a strong dependence of terahertz emission on bulk carrier concentration. The experimental results agree well with calculations based on drift-diffusion equations incorporating momentum conservation and relaxation.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.20.-i Conductivity phenomena in semiconductors and insulators

Room temperature, continuous wave operation of distributed feedback quantum cascade lasers with widely spaced operation frequencies

Andreas Wittmann, Marcella Giovannini, Jérôme Faist, Lubos Hvozdara, Stéphane Blaser, Daniel Hofstetter, and Emilio Gini

Appl. Phys. Lett. 89, 141116 (2006); http://dx.doi.org/10.1063/1.2358939 (3 pages) | Cited 25 times

Online Publication Date: 3 October 2006

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Lasing properties of room temperature, continuous wave operated distributed feedback (DFB) quantum cascade lasers are reported. A bound-to-continuum active region was used to generate a broad gain spectrum. As a result, first-order DFB lasers employing different periods allowed us to achieve single mode continuous wave emission at several wavelengths ranging from 7.7 to 8.3 μm at a temperature of +30 °C. The frequency span corresponds to 8% of the center frequency.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Detection of short lived radioisotopes as a fast diagnostic for intense laser-solid interactions

R. J. Clarke, K. W. D. Ledingham, P. McKenna, L. Robson, T. McCanny, D. Neely, O. Lundh, F. Lindau, C.-G. Wahlström, P. T. Simpson, and M. Zepf

Appl. Phys. Lett. 89, 141117 (2006); http://dx.doi.org/10.1063/1.2358940 (3 pages) | Cited 2 times

Online Publication Date: 3 October 2006

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As a diagnostic of high-intensity laser interactions (>1019 W cm−2), the detection of radioactive isotopes is regularly used for the characterization of proton, neutron, ion, and photon beams. This involves sample removal from the interaction chamber and time consuming post shot analysis using NaI coincidence counting or Ge detectors. This letter describes the use of in situ detectors to measure laser-driven (p,n) reactions in math as an almost real-time diagnostic for proton acceleration. The produced math isotope decays with a 4.16 s half-life by the predominantly β+ emission, producing a strong 511 keV annihilation peak.
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29.40.-n Radiation detectors
42.62.-b Laser applications

Feedback Mach-Zehnder resonator with “reflector:” Analysis and applications in single frequency fiber lasers

Shailesh Srivastava, Ram Gopal, Sivasankara Sai, and Krishnamurthy Srinivasan

Appl. Phys. Lett. 89, 141118 (2006); http://dx.doi.org/10.1063/1.2358212 (3 pages) | Cited 1 time

Online Publication Date: 4 October 2006

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The authors propose a resonant loop mirror configuration using two couplers and a weak reflecting element in the feedback arm. The analysis is carried out using the signal flow graph method. Narrow band reflection peaks can be produced using a wide choice of parameters. A Vernier effect in the two loops can lead to a tenfold increase in the free spectral range. These properties make the device more versatile than the earlier studied single coupler resonator with “reflector” and enhance its use in single frequency lasing.
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42.55.Wd Fiber lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
07.60.Ly Interferometers

Terahertz-wave generation in quasi-phase-matched GaAs

K. L. Vodopyanov, M. M. Fejer, X. Yu, J. S. Harris, Y.-S. Lee, W. C. Hurlbut, V. G. Kozlov, D. Bliss, and C. Lynch

Appl. Phys. Lett. 89, 141119 (2006); http://dx.doi.org/10.1063/1.2357551 (3 pages) | Cited 13 times

Online Publication Date: 4 October 2006

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The authors demonstrate an efficient room temperature source of terahertz radiation using femtosecond laser pulses as a pump and GaAs structures with periodically inverted crystalline orientation, such as diffusion-bonded stacked GaAs and epitaxially grown orientation-patterned GaAs, as a nonlinear optical medium. By changing the GaAs orientation-reversal period (504–1277 μm), or the pump wavelength (2–4.4 μm), we were able to generate narrow-bandwidth ( ∼ 100 GHz) terahertz wave packets, tunable between 0.9 and 3 THz, with the optical-to-terahertz photon conversion efficiency of 3.3%.
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78.66.Fd III-V semiconductors
42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Large-aperture switchable thin diffractive lens with interleaved electrode patterns

Guoqiang Li, Pouria Valley, M. S. Giridhar, David L. Mathine, Gerald Meredith, Joshua N. Haddock, Bernard Kippelen, and N. Peyghambarian

Appl. Phys. Lett. 89, 141120 (2006); http://dx.doi.org/10.1063/1.2338646 (3 pages) | Cited 9 times

Online Publication Date: 5 October 2006

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The authors report on a high-performance large-aperture switchable diffractive lens using nematic liquid crystal that can be used as an adaptive eyewear. The odd- and even-numbered ring electrodes are separated in two layers, avoiding the gaps between the neighboring electrodes and allowing high diffraction efficiency. It is easier to avoid shorts between neighboring conductive electrodes and fabricate lenses with larger aperture and smaller feature size. With a four-level phase modulation, a 15 mm aperture, 2 dpt lens with small aberrations and diffraction efficiency of above 75% could be demonstrated with low operating voltages. The thickness of the liquid crystal is only 5 μm. The lens switching time is about 180 ms. The on and off states of the electrically controlled lens allows near and distance vision, respectively. The focusing power of the lens can be adjusted to be either positive or negative. This structure can be extended to higher-level phase modulation with even higher efficiencies.
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42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.66.-p Physiological optics
42.15.Fr Aberrations

Nanocomposites with very large electro-optic effect and widely tunable refractive index

Q. Chen, M. R. Lin, J. E. Lee, Q. M. Zhang, and S. Yin

Appl. Phys. Lett. 89, 141121 (2006); http://dx.doi.org/10.1063/1.2360183 (3 pages) | Cited 12 times

Online Publication Date: 5 October 2006

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A very large electro-optic effect has been observed in relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer. By adding a small amount of zinc sulfide nanoparticles, the refractive index of the nanocomposite can be tuned between 1.4 and 1.5 while retaining a large electro-optic effect and high transparency. Tunable long-period fiber gratings have been fabricated with the polymer nanocomposite as the second cladding, and a resonance wavelength shift of over 50 nm has been achieved when electric field changed by 30 V/μm. This magnitude of shift corresponds to pure refractive index change of Δn/n ≈ 0.4% in the nanocomposite.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.80.-e Ferroelectricity and antiferroelectricity
42.79.Dj Gratings
42.81.Wg Other fiber-optical devices

GaN/AlGaN heterojunction infrared detector responding in 8–14 and 20–70 μm ranges

G. Ariyawansa, M. B. M. Rinzan, M. Strassburg, N. Dietz, A. G. U. Perera, S. G. Matsik, A. Asghar, I. T. Ferguson, H. Luo, and H. C. Liu

Appl. Phys. Lett. 89, 141122 (2006); http://dx.doi.org/10.1063/1.2360205 (3 pages) | Cited 9 times

Online Publication Date: 5 October 2006

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A GaN/AlGaN heterojunction interfacial work function internal photoemission infrared detector responding in 8–14 and 20–70 μm ranges has been demonstrated. Free carrier absorption based photoresponse shows a wavelength threshold of 14 μm with a peak responsivity of 0.6 mA/W at 80 K under −0.5 V bias. A sharp peak in the 11–13.6 μm range is observed superimposed on the free carrier response. In addition, the work demonstrates 54 μm (5.5 THz) operation of the detector based on 1s–2p± transition of Si donors in GaN. Possible approaches on improving the performance of the detector are also addressed.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.30.+y Surface double layers, Schottky barriers, and work functions

Enhanced light-extraction in GaInN near-ultraviolet light-emitting diode with Al-based omnidirectional reflector having NiZn/Ag microcontacts

Jong Kyu Kim, J.-Q. Xi, Hong Luo, E. Fred Schubert, Jaehee Cho, Cheolsoo Sone, and Yongjo Park

Appl. Phys. Lett. 89, 141123 (2006); http://dx.doi.org/10.1063/1.2360217 (3 pages) | Cited 10 times

Online Publication Date: 5 October 2006

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Enhancement of light extraction in a GaInN near-ultraviolet light-emitting diode (LED) employing an Al-based omnidirectional reflector (ODR) consisting of GaN, a SiO2 low-refractive-index layer perforated by an array of NiZn/Ag microcontacts, and an Al layer is presented. A theoretical calculation reveals that a SiO2/Al ODR has much higher reflectivity than both a SiO2/Ag ODR and a Ag reflector at a wavelength of 400 nm. It is experimentally shown that GaInN near-ultraviolet LEDs with GaN/SiO2/Al ODR have 16% and 38% higher light output than LEDs with SiO2/Ag ODR and Ag reflector, respectively. The higher light output is attributed to enhanced reflectivity of the Al-based ODR in the near-ultraviolet wavelength range.
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85.60.Jb Light-emitting devices

Demonstration of net gain at 1550 nm in an erbium-doped polymersingle mode rib waveguide

Anh Quoc Le Quang, Rolland Hierle, Joseph Zyss, Isabelle Ledoux, Giuseppe Cusmai, Raffaella Costa, Angelo Barberis, and Silvia Maria Pietralunga

Appl. Phys. Lett. 89, 141124 (2006); http://dx.doi.org/10.1063/1.2360179 (3 pages) | Cited 17 times

Online Publication Date: 6 October 2006

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A polymer-based waveguide optical amplifier doped with Er3+ ions has been modeled, fabricated, and characterized. Propagation losses have been measured using both cutback and Fabry-Pérot methods, resulting in similar, reasonable loss values that do not exceed 1.31 dB cm−1 at 1540 nm. By accounting for overall propagation loss, a net gain of 1.34 dB at 1540 nm is demonstrated for a 1.6 cm long single mode waveguide amplifier.
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42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics

Real-time terahertz imaging over a standoff distance (>25 meters)

Alan W. M. Lee, Qi Qin, Sushil Kumar, Benjamin S. Williams, Qing Hu, and John L. Reno

Appl. Phys. Lett. 89, 141125 (2006); http://dx.doi.org/10.1063/1.2360210 (3 pages) | Cited 58 times

Online Publication Date: 6 October 2006

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Show Abstract
The authors demonstrate the use of a terahertz quantum cascade laser (QCL) for real-time imaging in transmission mode at a standoff distance of 25 meters. Lasing frequency was selected for optimum transmission within an atmospheric window at ∼ 4.9 THz. Coarse frequency selection was made by design of the QCL gain medium. Finer selection (to within 0.1 THz) was made by judicious choice of laser cavity length to adjust facet losses and therefore lasing threshold bias, in order to overlap the peak frequency of the Stark-shifted gain spectrum with the atmospheric window. Images are shown using an uncooled 320×240 microbolometer camera.
Show PACS
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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