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23 Sep 2002

Volume 81, Issue 13, pp. 2319-2480

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Efficient polarized light-emitting diodes utilizing ultrathin photoaddressable alignment layers

X. H. Yang, D. Neher, S. Lucht, H. Nothofer, R. Güntner, U. Scherf, R. Hagen, and S. Kostromine

Appl. Phys. Lett. 81, 2319 (2002); http://dx.doi.org/10.1063/1.1509117 (3 pages) | Cited 14 times

Online Publication Date: 16 September 2002

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We demonstrate that an ultrathin photoaddressable polymer (PAP) layer with a thickness as small as 5 nm can be utilized for the monodomain alignment of thermotropic liquid crystalline polyfluorene. The optical anisotropies in absorption and emission are found to be independent of the PAP layer thickness within a range of 5 to 30 nm. On the other hand, decreasing the PAP layer thickness greatly improves the performance of polarized blue light-emitting diodes: With a PAP layer thickness of only 10 nm, the device turns on at 5 V and reaches a brightness of 100 cd/m2 at 8 V with an efficiency of 0.66 cd/A. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics

Third-order nonlinear optical properties of in-backbone substituted conjugated polymers

U. Gubler, S. Concilio, Ch. Bosshard, I. Biaggio, P. Günter, R. E. Martin, M. J. Edelmann, J. A. Wytko, and F. Diederich

Appl. Phys. Lett. 81, 2322 (2002); http://dx.doi.org/10.1063/1.1507834 (3 pages) | Cited 16 times

Online Publication Date: 16 September 2002

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We present an alternative approach to tune the third-order nonlinear optical properties of organic molecules by inserting a functional group into the path of the π-electron conjugation instead of at its ends. We show that this scheme has a beneficial influence on the second-order hyperpolarizability for short molecules, but that in two instances where such molecules were polymerized into longer molecules the overall hyperpolarizability is reduced. © 2002 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
42.70.Jk Polymers and organics

Resolution of photonic crystal superprism

Toshihiko Baba and Takashi Matsumoto

Appl. Phys. Lett. 81, 2325 (2002); http://dx.doi.org/10.1063/1.1508813 (3 pages) | Cited 40 times

Online Publication Date: 16 September 2002

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We theoretically investigated the performance of the photonic crystal superprism, that is, the propagating beam quality, the wavelength sensitivity, and the resolution as a narrow band filter at 1.5-μm-wavelength range. First, we defined the equi-incident-angle curve in the Brillouin zone. Next, we mapped three parameters that represented the abovementioned performance over the Brillouin zone. As a result, we found a narrow design window that allows a high resolution of 0.4 nm along an equi-incident-angle curve but requires an incident beam width of over 100 μm and a device length of centimeter order. It can be an essential high efficiency filter if the input end of the crystal is optimized and the propagation loss is suppressed. © 2002 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
42.70.Qs Photonic bandgap materials
42.79.Ci Filters, zone plates, and polarizers

High-repetition rate femtosecond laser-driven hard-x-ray source

A. Egbert, B. Mader, B. Tkachenko, C. Fallnich, B. N. Chichkov, H. Stiel, and P. V. Nickles

Appl. Phys. Lett. 81, 2328 (2002); http://dx.doi.org/10.1063/1.1509858 (3 pages) | Cited 6 times

Online Publication Date: 16 September 2002

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A compact, high-repetition rate, ultrashort-pulse laser-driven hard-x-ray source based on the combination of a femtosecond laser system with an x-ray diode is demonstrated. A comparison with available laser-plasma sources is presented. Numerical modeling is performed which proves that picosecond and subpicosecond hard-x-ray pulses can be produced with this source. © 2002 American Institute of Physics.
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42.55.Vc X- and γ-ray lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Enhanced blue and green emission in rare-earth-doped GaN electroluminescent devices by optical photopumping

D. S. Lee and A. J. Steckl

Appl. Phys. Lett. 81, 2331 (2002); http://dx.doi.org/10.1063/1.1509111 (3 pages) | Cited 20 times

Online Publication Date: 16 September 2002

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Electroluminescence (EL) from rare-earth-doped GaN (GaN:RE) EL devices (ELD) emission has been observed to be greatly enhanced by ultraviolet (UV) photopumping. With radiation from a HeCd laser (325 nm) both blue (from GaN:Tm) and green (from GaN:Er) EL brightness have been enhanced up to 2 orders of magnitude, depending on bias conditions. We explain the luminescence increase by the following mechanism: photoelectrons generated by above GaN band-gap excitation are accelerated by the electric field along with electrically injected electrons and both types of carriers contribute to EL emission through RE impact excitation. The EL intensity increases monotonically with increasing applied bias and with photopumping power. The photopumped-induced EL gain is most efficient at relatively low bias, reaching values of 50–100×. This increase in EL emission can be applied to flat panel displays with enhanced brightness, especially blue, and with improved color balance. Other applications include UV indicators and detectors, and infrared emitters. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Properties of highly strained InGaAs/GaAs quantum wells for 1.2-μm laser diodes

S. Mogg, N. Chitica, R. Schatz, and M. Hammar

Appl. Phys. Lett. 81, 2334 (2002); http://dx.doi.org/10.1063/1.1509478 (3 pages) | Cited 11 times

Online Publication Date: 16 September 2002

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The properties of 1.2-μm highly strained InGaAs quantum wells (QWs) grown on GaAs substrates have been analyzed. Optical gain spectra versus injection current and temperature, transparency current density, as well as other figures of merit were assessed from measurements on broad-area and ridge-waveguide lasers based on these QWs. Such active regions are of interest for a range of applications, including GaAs-based high-power lasers and vertical-cavity lasers for wavelengths beyond 1.2 μm. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Field-controlled optical profile of a waveguide having a liquid-crystalline core

M. Marangoni, R. Osellame, R. Ramponi, M. Buscaglia, T. Bellini, and F. Mantegazza

Appl. Phys. Lett. 81, 2337 (2002); http://dx.doi.org/10.1063/1.1508167 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2002

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The optical properties of a nematic liquid-crystal waveguide in a hybrid configuration have been dynamically reshaped in a straightforward and controlled way by applying an external electric field. The anisotropic refractive index profile of the waveguide has been determined for different electric-field strengths by means of m-lines spectroscopy. The experimental results are in very good agreement with the values predicted by a simple model that takes into account the dielectric, optical, and elastic properties of the liquid-crystal guiding layer. © 2002 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.20.Jq Electro-optical effects

Transmission spectroscopy of photonic crystals in a silicon-on-insulator waveguide structure

M. Zelsmann, E. Picard, T. Charvolin, E. Hadji, B. Dal’zotto, M. E. Nier, C. Seassal, P. Rojo-Romeo, and X. Letartre

Appl. Phys. Lett. 81, 2340 (2002); http://dx.doi.org/10.1063/1.1507614 (3 pages) | Cited 10 times

Online Publication Date: 16 September 2002

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Optical properties of two-dimensional photonic crystals (PCs) integrated in a silicon-on-insulator stripe waveguide are reported. Transmission measurements are done on a wide wavelength range (1.1–1.7 μm) by coupling a white-light source in the cleaved edge of the sample and collecting light at the other cleaved side of the waveguide. PC mirrors and one-dimensional (1D) Fabry–Pérot cavities formed between two PC reflectors have been fabricated and characterized. The photonic band gap of the mirror is observed in the Γ–M direction for the transverse electric like guided modes. For the waveguide with the 1D Fabry–Pérot cavity, resonant modes appear within the gap. It is found that the experimental spectra are in very good agreement with both the theoretical photonic band structure and the theoretical transmission calculated by finite difference time domain. © 2002 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.50.-p Quantum optics
42.70.Qs Photonic bandgap materials
78.20.-e Optical properties of bulk materials and thin films
02.70.Bf Finite-difference methods
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