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8 Mar 2004

Volume 84, Issue 10, pp. 1623-1807

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1798 (2004); http://dx.doi.org/10.1063/1.1664019 (3 pages)

Bartosz A. Grzybowski, Michal Radkowski, Christopher J. Campbell, Jessamine Ng Lee, and George M. Whitesides
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Fabrication of planar optical waveguides by electrical microcontact printing

Daniel B. Wolfe, J. Christopher Love, Byron D. Gates, George M. Whitesides, Richard S. Conroy, and Mara Prentiss

Appl. Phys. Lett. 84, 1623 (2004); http://dx.doi.org/10.1063/1.1651329 (3 pages) | Cited 20 times

Online Publication Date: 2 March 2004

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This letter describes the fabrication by electrical microcontact printing (E-μCP) of planar, optical waveguides, and splitters made of poly(4-vinylphenol) doped with phloxine B. This soft-lithographic technique uses a poly(dimethylsiloxane) (PDMS) stamp coated with a thin gold film to pattern the flow of current through the film of doped polymer. The current bleaches the phloxine B, and thus creates regions of high (unbleached; waveguide core) and low (bleached; waveguide cladding) refractive index. The maximum exposure time to obtain Δn = 0.025 was 90 s. This system is useful for guiding light having λ = 600–1310 nm. These polymer waveguides preserve polarization, and are able to guide light around 90° corners with a minimum radius of curvature of 1.6 mm. E-μCP patterned a 1×4 optical power splitter in 10 s. This technique is potentially useful for rapid prototyping of planar and multilevel optical devices. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Recording of polarization holograms in photodarkened amorphous chalcogenide films

K. E. Asatryan, S. Frédérick, T. Galstian, and R. Vallée

Appl. Phys. Lett. 84, 1626 (2004); http://dx.doi.org/10.1063/1.1666999 (3 pages) | Cited 8 times

Online Publication Date: 2 March 2004

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Polarization gratings were recorded in amorphous As2S3 chalcogenide thin films in three orthogonal recording configurations. The analysis of polarization discrimination properties of such vector gratings revealed a poor performance. It was shown that the main reason for this is the presence of nondesired scalar modulation of the same period. An exception is (s+p) recording configuration, where a pure polarization grating may be obtained even for relatively high photoexposures. © 2004 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.40.Ht Hologram recording and readout methods
42.70.Gi Light-sensitive materials
61.43.Fs Glasses
78.66.Jg Amorphous semiconductors; glasses

Multiple channeled phenomena in heterostructures with defects mode

Zhanshan Wang, Li Wang, Yonggang Wu, Lingyan Chen, Xiaoshuang Chen, and Wei Lu

Appl. Phys. Lett. 84, 1629 (2004); http://dx.doi.org/10.1063/1.1651650 (3 pages) | Cited 47 times

Online Publication Date: 2 March 2004

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Transmission studies for multiple heterostructures inserted with defects are presented. The results show that the enlargement of the forbidden band and the realization of multiple channeled filtering can be reached simultaneously with these configurations. The frequency, frequency interval, and number of channels can be tuned by adjusting geometric and physical parameters of the defects. Sidebands of the forbidden band can be substantially restricted as compared with that of periodic structures. Experimental fabrication of the designed configurations is carried out with the heterostructures containing TiO2/SiO2 multilayer defects, and the results agree with the calculation very well. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials

Two-photon lasing of dye-doped photonic crystal lasers

Koichiro Shirota, Hong-Bo Sun, and Satoshi Kawata

Appl. Phys. Lett. 84, 1632 (2004); http://dx.doi.org/10.1063/1.1666996 (3 pages) | Cited 10 times

Online Publication Date: 2 March 2004

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We report two-photon pump lasing action of a photonic crystal laser, which comprises fluorescent dye-doped chiral nematic liquid crystals. The dye absorbs light peaking at 466 nm, while the pumping was conducted at 1000 nm wavelength. Due to redistribution of density of states by a stopping band, a strong single-mode stimulated emission was observed at the band edge wavelength of 608 nm with 1 nm detection-limited linewidth. A comparative study shows that under an identical pumping geometry, the two-photon lasing threshold is only 120 times larger than that for the single-photon excitation, a ratio lower than those generally reported for up-conversion lasing. © 2004 American Institute of Physics.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Mv Dye lasers
42.70.Qs Photonic bandgap materials
78.45.+h Stimulated emission
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
78.55.Bq Liquids

A monochromatic and high-power terahertz source tunable in the ranges of 2.7–38.4 and 58.2–3540 μm for variety of potential applications

Wei Shi and Yujie J. Ding

Appl. Phys. Lett. 84, 1635 (2004); http://dx.doi.org/10.1063/1.1649802 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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Based on phase-matched collinear difference-frequency generation in a single GaSe crystal, continuously tunable and coherent radiation in the extremely wide ranges of 2.7–38.4 and 58.2–3540 μm has been achieved. This unique source has the additional advantages of high coherence (narrow linewidth) and simple alignment. The peak output power for the terahertz radiation reaches 209 W at the wavelength of 196 μm (1.53 THz), which corresponds to a power conversion efficiency of 0.055%. Moreover, the terahertz transmission spectra on DNA macromolecules and protein were directly measured, demonstrating some potential and important applications of this terahertz source. © 2004 American Institute of Physics.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
42.72.Ai Infrared sources
87.14.E- Proteins
87.14.G- Nucleic acids
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
87.80.-y Biophysical techniques (research methods)

Temperature-insensitive Ge–B–SiO2 planar lightwave circuits by inductively coupled plasma-enhanced chemical vapor deposition

Q. Y. Zhang, K. Pita, L. P. Zuo, and S. Takahashi

Appl. Phys. Lett. 84, 1638 (2004); http://dx.doi.org/10.1063/1.1664011 (3 pages) | Cited 3 times

Online Publication Date: 2 March 2004

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Low-propagation-loss Ge–B–SiO2 planar waveguides have been achieved by inductively coupled plasma-enhanced chemical vapor deposition. The significant effects due to annealing temperature, hydrogen loading, and KrF excimer ultraviolet laser irradiation on the optical properties of Ge–B–SiO2 films have been investigated. A temperature-insensitive Mach–Zehnder interferometer-like optical filter has been demonstrated by means of a double-core fabrication method using 10GeO2–90SiO2 (10G90S) and 8GeO2–5B2O3–87SiO2 (8G5B87S) as two different waveguide cores. We have achieved less than 0.5 pm/°C temperature dependence of the central wavelength of the filter at 1550 nm while varying the temperature from −20 to 80 °C. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments

Thermal decomposition of a thin AgOx layer generating optical near-field

A. V. Kolobov, A. Rogalev, F. Wilhelm, N. Jaouen, T. Shima, and J. Tominaga

Appl. Phys. Lett. 84, 1641 (2004); http://dx.doi.org/10.1063/1.1667003 (3 pages) | Cited 16 times

Online Publication Date: 2 March 2004

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Thermal decomposition of AgOx thin layers generating optical near field have been studied by Ag LIII edge x-ray absorption near-edge structure. We found that, different from previous assumptions, the starting layer is a mixture of AgO (∼40%) and Ag2O (∼60%). We further observed that thermal decomposition starts at a temperature as low as 50 °C. The decomposition process exhibits three stages and the oxide layer at intermediate stages consists of a mixture of AgO, Ag2O, and metallic Ag with different fractions of each phase. Activation energies of the decomposition of the thin oxide layer have been determined for different decomposition stages, the obtained values being different from that for powder oxides. © 2004 American Institute of Physics.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.70.Dm X-ray absorption spectra

Extended phase matching of second-harmonic generation in periodically poled KTiOPO4 with zero group-velocity mismatch

Friedrich König and Franco N. C. Wong

Appl. Phys. Lett. 84, 1644 (2004); http://dx.doi.org/10.1063/1.1668320 (3 pages) | Cited 16 times

Online Publication Date: 2 March 2004

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Under extended phase-matching conditions, the first frequency derivative of the wave-vector mismatch is zero and the phase-matching bandwidth is greatly increased. We present extensive three-wave mixing measurements of the wave-vector mismatch and obtain improved Sellmeier equations for KTiOPO4. We observed a type-II extended phase-matching bandwidth of 100 nm for second-harmonic generation in periodically poled KTiOPO4, centered at the fundamental wavelength of 1584 nm. Applications in quantum entanglement and frequency metrology are discussed. © 2004 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
06.30.Ft Time and frequency
42.50.-p Quantum optics

Application of strontium silicate yellow phosphor for white light-emitting diodes

Joung Kyu Park, Chang Hae Kim, Seung Hyok Park, Hee Dong Park, and Se Young Choi

Appl. Phys. Lett. 84, 1647 (2004); http://dx.doi.org/10.1063/1.1667620 (3 pages) | Cited 145 times

Online Publication Date: 2 March 2004

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In order to develop a yellow phosphor that emits efficiently under the 450–470 nm excitation range, we have synthesized a Eu2+-activated Sr3SiO5 yellow phosphor and attempted to develop white light-emitting diodes (LEDs) by combining them with a InGaN blue LED chip (460 nm). Two distinct emission bands from the InGaN-based LED and the Sr3SiO5:Eu phosphor are clearly observed at 460 nm and at 570 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that InGaN (460 nm chip)-based Sr3SiO5:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460 nm chip)-based YAG:Ce. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.55.Hx Other solid inorganic materials

Dynamic filamentation and beam quality of quantum-dot lasers

E. Gehrig, O. Hess, C. Ribbat, R. L. Sellin, and D. Bimberg

Appl. Phys. Lett. 84, 1650 (2004); http://dx.doi.org/10.1063/1.1668330 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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We present a comparative study of numerical simulations and experiments on the spatiotemporal dynamics and emission characteristics of quantum-well and quantum-dot lasers of identical structure. They show that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude–phase coupling enable a significant improvement of beam quality compared to quantum-well lasers of identical geometry. Near-field profiles and beam quality (M2) parameters calculated on the basis of time-dependent effective Maxwell–Bloch equations into which the physical properties of the active media are included via space-dependent material parameters, effective time constants, and matrix elements are fully confirmed by experimental measurements. Together they indicate that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude–phase coupling enable a significant improvement of beam quality compared with quantum-well lasers of identical geometry. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics
85.30.De Semiconductor-device characterization, design, and modeling

Fluorene-based low band-gap copolymers for high performance photovoltaic devices

Qingmei Zhou, Qiong Hou, Liping Zheng, Xianyu Deng, Gang Yu, and Yong Cao

Appl. Phys. Lett. 84, 1653 (2004); http://dx.doi.org/10.1063/1.1667614 (3 pages) | Cited 87 times

Online Publication Date: 2 March 2004

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Low band-gap, soluble conjugated copolymers were synthesized from 9,9-dioctylfluorene and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (PFO-DBT) and different composition ratios were used for the donor material in bulk heterojunction polymer photovoltaic cells (PVCs). In PVCs made with PFO-DBT:PCBM (methano-fullerene [6,6]-phenyl C61-butyric acid methyl ester) blends, the spectral response is extended up to 650 nm and the open-circuit voltage (Voc) is improved to 0.95 V. The energy conversion efficiency (ηe) in devices with optimized composition reaches 2.24% under an AM1.5 solar simulator (78.2 mW/cm2). In contrast to organic PVCs previously published, these PVCs retain high energy conversion efficiency at illumination up to 5 suns of AM1.5 spectral illumination. This feature allows high efficiency polymer PVC modules made in combination with a light concentrator. © 2004 American Institute of Physics.
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82.35.Jk Copolymers, phase transitions, structure
61.41.+e Polymers, elastomers, and plastics
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
68.55.-a Thin film structure and morphology
78.40.Pg Disordered solids
78.30.Jw Organic compounds, polymers
42.70.Jk Polymers and organics

Tunable and white light-emitting diodes of monolayer fluorinated benzoxazole graft copolymers

S. J. Bai, C. C. Wu, T. D. Dang, F. E. Arnold, and B. Sakaran

Appl. Phys. Lett. 84, 1656 (2004); http://dx.doi.org/10.1063/1.1667262 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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Coil-like graft copolymers of poly(Am-co-B(1−m)) containing identical heterocyclic aromatic benzoxazole with trifluoromethyl-ethyl as the backbone and pendants of monohydroxl (Am) and/or bidecyloxyl (B(1−m)) on their phenylene ring were studied for luminescence properties. The copolymers were synthesized with molar fraction m ranging from 0, 0.25, 0.5, 0.75, to 1, and then dissolved and spun onto a Spectrosil® quartz slide or an indium-tin-oxide (ITO) substrate. The fluorescence properties of copolymers were investigated by ultraviolet–visible absorption covering 185 nm to 800 nm and photoluminescence (PL) emission excited at 363 nm. The PL results exhibited an excellent chromatic tuning, ranging from green to white emission as m decreased. Aluminum electron injectors were evaporated onto the copolymer/ITO unit making it into monolayer light-emitting diodes for current–voltage and electroluminescence (EL) responses. An emission threshold voltage of 6 V was achieved for all the monolayer copolymer devices. The Commission Internationale de l’Eclairage coordinates of the EL emission were from (0.25, 0.53) to (0.24,0.31) covering a wide visible range including white light emission. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
42.70.Jk Polymers and organics
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.41.+e Polymers, elastomers, and plastics
78.66.Qn Polymers; organic compounds
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Broadband tuning of external cavity bound-to-continuum quantum-cascade lasers

Richard Maulini, Mattias Beck, Jérôme Faist, and Emilio Gini

Appl. Phys. Lett. 84, 1659 (2004); http://dx.doi.org/10.1063/1.1667609 (3 pages) | Cited 51 times

Online Publication Date: 2 March 2004

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A quantum-cascade structure based on a bound-to-continuum design exhibiting a broad gain curve is presented. The full width at half maximum of the measured luminescence spectrum is 297 cm−1 at room temperature. Grating-coupled external cavity lasers using this active region could be tuned over 150 cm−1 (1.45 μm), which is equal to 15% of the free running wavelength (λ ≅ 10 μm), in pulsed mode at room temperature. Time resolved spectra showed a single-mode operation with a 30 dB side mode suppression ratio after the first 12 ns of the pulse. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.60.Fi Electroluminescence
78.47.-p Spectroscopy of solid state dynamics
78.67.De Quantum wells

Periodically poled near-stoichiometric lithium tantalate for optical parametric oscillation

Nan Ei Yu, Sunao Kurimura, Yoshiyuki Nomura, Masaru Nakamura, Kenji Kitamura, Jun Sakuma, Yoshio Otani, and Akira Shiratori

Appl. Phys. Lett. 84, 1662 (2004); http://dx.doi.org/10.1063/1.1667616 (3 pages) | Cited 18 times

Online Publication Date: 2 March 2004

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A 35-mm-long periodically poled device was fabricated from a near-stoichiometric lithium tantalate, and optical parametric oscillation was demonstrated with a low oscillation threshold (106 mW). The emitted signal and idler wavelengths were 1.53–1.63 and 3.06–3.49 μm, respectively, and the highest slope conversion efficiency was 65% with a maximum output power of 628 mW at 1.1 W pumping. The influence of Curie temperature inhomogeneity on fabrication of the device was investigated to improve poling quality in long devices. © 2004 American Institute of Physics.
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42.65.Yj Optical parametric oscillators and amplifiers
77.22.Ej Polarization and depolarization
61.66.Bi Elemental solids
61.66.Dk Alloys

Single dye molecules in an oxygen-depleted environment as photostable organic triggered single-photon sources

Y. Lill and B. Hecht

Appl. Phys. Lett. 84, 1665 (2004); http://dx.doi.org/10.1063/1.1667591 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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We demonstrate, that under nitrogen atmosphere, 20% of single DiIC18(3) (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) molecules in poly(methylmethacrylate) show an extremely low photobleaching quantum yield of (4.66±0.07)×10−8 together with a reasonably short triplet lifetime. We exploit these properties to demonstrate that the system can be used to produce a triggered single-photon source based exclusively on organic materials. © 2004 American Institute of Physics.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
78.55.Kz Solid organic materials
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