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23 Oct 2000

Volume 77, Issue 17, pp. 2629-2769

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Enhanced wavelength tuning of an InGaAsP-InP laser with a thermal-strain-magnifying trench

D. A. Cohen, B. Mason, J. Dolan, C. Burns, and L. A. Coldren

Appl. Phys. Lett. 77, 2629 (2000); http://dx.doi.org/10.1063/1.1319527 (3 pages) | Cited 4 times

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We have used temperature-dependent strain from differential thermal expansion to increase the temperature tuning rate, dλ/dT, of the modal wavelength of an InP-based laser. The effectiveness of the strain may be further enhanced with a deep trench etch beneath the laser waveguide. We have obtained a 50% increase in the tuning rate, without degradation of the threshold current, and a maximum increase of 86%. © 2000 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
65.40.De Thermal expansion; thermomechanical effects
81.65.Cf Surface cleaning, etching, patterning
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Optically resolving dynamic processes in commercial liquid crystal cells

N. J. Smith and J. R. Sambles

Appl. Phys. Lett. 77, 2632 (2000); http://dx.doi.org/10.1063/1.1319533 (3 pages) | Cited 11 times

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The recently developed fully leaky guided mode technique is a powerful tool for accurately resolving the director profile in standard, commercially fabricated liquid crystal cells. By employing a convergent beam to simultaneously excite many fully leaky guided modes, angular dependent reflectivity and transmissivity data can be captured in a fraction of a millisecond with a charge coupled device array, thus enabling the switching dynamics of the liquid crystal cell to be resolved. A preliminary study of the director profile (optical tensor distribution) during the relaxation of a homogeneously aligned cell (antiparallel rubbed) filled with the nematic material ZLI-2293 is presented here. By resolving the director distribution as a function of time, the time constant for the relaxation process is obtained from which the effective rotational viscosity coefficient γ∗ is then evaluated. © 2000 American Institute of Physics.
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42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
78.20.Jq Electro-optical effects
66.20.-d Viscosity of liquids; diffusive momentum transport

Efficient photovoltaic cells from semiconducting polymer heterojunctions

Samson A. Jenekhe and Shujian Yi

Appl. Phys. Lett. 77, 2635 (2000); http://dx.doi.org/10.1063/1.1320022 (3 pages) | Cited 91 times

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Solar cells made from spin-coated bilayer thin-film heterojunctions of poly(p-phenylene vinylene) and poly(benzimidazobenzophenanthroline ladder) were found to have photovoltaic charge collection efficiency as high as 49%. The power conversion efficiency varied from 1.4% under sunlight illumination to 2.0% at the peak wavelength. A space-charge region around the polymer/polymer interface, Ohmic contacts at the electrodes, and complementary absorption bands of the semiconducting polymers, play important roles in the efficient charge collection in the photocells. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ph Polymers; organic compounds

Near-field fiber tip to handle high input power more than 150 mW

S. T. Jung, D. J. Shin, and Y. H. Lee

Appl. Phys. Lett. 77, 2638 (2000); http://dx.doi.org/10.1063/1.1320035 (3 pages) | Cited 4 times

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A high-power near-field fiber tip is proposed and demonstrated. This high-power tip can handle an optical power of greater than 150 mW injected into the fiber core, higher than any previous tip. The tip has a unique, thick, heat-conducting metal layer deposited by an electroplating process. The subwavelength aperture of the tip is fabricated by the controlled lapping of the end face with in situ optical monitoring. We also demonstrate using this tip to record on phase change and photoresist media. © 2000 American Institute of Physics.
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07.60.Vg Fiber-optic instruments
42.81.Wg Other fiber-optical devices
07.79.Fc Near-field scanning optical microscopes

Organic solid-state distributed feedback dye laser with a nonmorphological modification grating

Michifumi Nagawa, Musubu Ichikawa, Toshiki Koyama, Hirofusa Shirai, Yoshio Taniguchi, Akihito Hongo, Shinji Tsuji, and Yoshiaki Nakano

Appl. Phys. Lett. 77, 2641 (2000); http://dx.doi.org/10.1063/1.1320034 (3 pages) | Cited 21 times

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We report an organic solid-state distributed feedback laser consisting of an organic active layer and a Bragg grating without morphological change. The active layer consists of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostryl)-4H-pyran as a laser dye, tris(8hydroxyquinoline) aluminum as a host, and poly(methyl methacrylate) as a binder. The threshold and linewidth of the laser are 400 μJ/cm2 and 1.5 nm, respectively. With this laser, the Bragg grating exists out of the active layer and the grating surface is flat, which are very important for device fabrication and electric driving of the laser. © 2000 American Institute of Physics.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.70.Hj Laser materials
42.55.Rz Doped-insulator lasers and other solid state lasers
42.79.Dj Gratings

Optical alignment and fixation of liquid crystals using azopolymer networks

Yue Zhao, Yanick Chénard, and Tigran V. Galstian

Appl. Phys. Lett. 77, 2644 (2000); http://dx.doi.org/10.1063/1.1320461 (3 pages) | Cited 2 times

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Anisotropic gels of a nematic liquid crystal (NLC) were prepared using optical alignment and fixation in the absence of surface orientation layers. The method consists of first making a homogeneous mixture that contains a reactive diacrylate monomer bearing azobenzene group, a nonreactive NLC and a photoinitiator, then irradiating the mixture by a laser at λ = 532 nm for the liquid crystal (LC) orientation induction. Subsequently, the mixture is exposed by a second laser at λ = 350 nm for photopolymerization giving rise to anisotropic azobenzene network. Infrared dichroism measurements show that a remnant long-range LC orientation is retained by the network. © 2000 American Institute of Physics.
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42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
78.20.Fm Birefringence
78.30.C- Liquids
82.70.Gg Gels and sols
82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
42.62.-b Laser applications

Distributed-feedback sol-gel dye laser tunable in the near ultraviolet

Xiao-lei Zhu and Dennis Lo

Appl. Phys. Lett. 77, 2647 (2000); http://dx.doi.org/10.1063/1.1320454 (3 pages) | Cited 12 times

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Laser emission in the near ultraviolet region was observed from a distributed-feedback solid-state dye laser based on Exalite 377E dye-doped sol-gel silica slabs. The output performance of the laser was studied in detail. Pumped at 308 nm, wavelength tuning from 367 to 383 nm with the emission linewidth of 80 pm has been achieved. Exalite 377E-doped sol-gel silica distributed feedback laser showed a slope efficiency of 4.4% and a pump energy threshold of approximately 100 μJ (15 mJ/cm2 in energy density). The variation of output energy as a function of the number of pump pulse at 0.5 Hz repetition rate was also investigated. © 2000 American Institute of Physics.
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42.55.Mv Dye lasers
42.60.Fc Modulation, tuning, and mode locking
42.70.Hj Laser materials
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)
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Investigation of the sites of dark spots in organic light-emitting devices

Yoon-Fei Liew, Hany Aziz, Nan-Xing Hu, Hardy Sze-On Chan, Gu Xu, and Zoran Popovic

Appl. Phys. Lett. 77, 2650 (2000); http://dx.doi.org/10.1063/1.1320459 (3 pages) | Cited 60 times

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Poor environmental stability has been a major concern for organic light-emitting devices. Exposure to ambient conditions leads to the formation of nonemissive areas (dark spots) that result in a decrease in device luminescence. Although a number of mechanisms for the formation of dark spots have been proposed, the causes underlying their initiation, and their nucleation sites are still far from being clear. In this study, optical microscopy is used to investigate the sites of dark spots of devices in which the original cathodes are peeled off and replaced by newer cathodes. Results confirm that the growth of dark spots occurs primarily due to cathode delamination. The growth of dark spots is also associated with changes in the organic layers, especially at the organic/cathode interface. Results also suggest that the nucleation of dark spots takes place at the organic/cathode interface and originates during the deposition of the cathode. On the other hand, both the anode and the hole transport layer do not appear to play a role in the formation of dark spots. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Ht Other nonmetals

Chemical bonding state analysis of silicon carbide layers in Mo/SiC/Si multilayer mirrors by soft x-ray emission and absorption spectroscopy

Yasuji Muramatsu, Hisataka Takenaka, Yuko Ueno, Eric M. Gullikson, and Rupert C. C. Perera

Appl. Phys. Lett. 77, 2653 (2000); http://dx.doi.org/10.1063/1.1318231 (3 pages) | Cited 7 times

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Soft x-ray emission and absorption spectra in the C K region of Mo/SiC/Si multilayer mirrors were measured using highly brilliant synchrotron radiation to identify the chemical bonding states of the buried silicon carbide layers. Comparison with the C 2p density of state (DOS) spectra, calculated by discrete variational-Xα molecular orbital calculations, of several SiC-based cluster models showed that the measured x-ray spectra approximately agreed with the calculated C 2p–DOS spectra of the c- and h-SiC-based SiCx models in which some silicon atoms were replaced by carbon atoms. The chemical bonding states of the silicon carbide layers in the Mo/SiC/Si multilayer mirrors were therefore estimated to be carbon-excessive silicon carbide. © 2000 American Institute of Physics.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Wc Optical coatings
42.79.Bh Lenses, prisms and mirrors
78.66.-w Optical properties of specific thin films
78.70.En X-ray emission spectra and fluorescence
61.50.Lt Crystal binding; cohesive energy
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Analysis of spatial light modulation characteristics of C60

Sukhdev Roy, C. P. Singh, and K. P. J. Reddy

Appl. Phys. Lett. 77, 2656 (2000); http://dx.doi.org/10.1063/1.1320033 (3 pages) | Cited 6 times

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Spatial light modulation based on nonlinear absorption of light by excited-state molecules in C60–toluene solution is demonstrated. Amplitude modulation of probe laser beam transmissions at 747 and 885 nm, corresponding to the peak absorption of T1 and S1 states, by the modulation laser beam intensity induced population changes at 532 nm has been analyzed using the rate equation approach, for various values of the small-signal absorption coefficient. It is shown that for T1 and S1 states, modulation up to 100% and 94.5% can be achieved for a laser beam intensity of 800 W/cm2 and 1 kW/cm2 at 532 nm, respectively. © 2000 American Institute of Physics.
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78.66.Tr Fullerenes and related materials
42.79.Hp Optical processors, correlators, and modulators
42.30.Lr Modulation and optical transfer functions
78.20.Bh Theory, models, and numerical simulation
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