摘要:

Diffractive gratings with period varied by an electric field are developed using a cholesteric liquid crystal confined between two transparent electrodes with unidirectionally treated alignment layers. In the initial state (zero field), the cholesteric layers are parallel to the cell planes. The electric field creates an in-plane modulated structure of variable period. Diffraction regimes of both Raman-Nath and Bragg types are demonstrated. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120325

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Single-layer light emitting diodes (LEDs) were fabricated using poly[bis(p-butylphenyl)silane] as the emissive layer. An efficient and stable electroluminescence with a maximum at 407 nm was observed at room temperature under a forward electric field greater than6×105 V/cm.The coincidence of electroluminescence with photoluminescence suggests the origin of the electroluminescence in an excited silicon chain segment. The high external quantum efficiency (0.1&percent; photons/electron), narrow emission (full width at halfmaximum=15 nm), improved operating stability, and good solubility in organic solvents provide the possibility of using polysilanes for ultraviolet LEDs. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120326

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We show that permanent optical waveguides can be formed in various bulk glasses by photoinduced refractive index change with an ultrashort pulse laser. The waveguides were fabricated by focusing the laser beam through an microscope objective and translating the sample parallel to the axis of the laser beam. From the observations of intensity distributions in the output of guided light by a CCD camera, we demonstrated that permanent optical waveguides can be successfully formed in various glasses. In addition, from the analysis of a near-field pattern, it was confirmed that single mode waveguides of the graded index type can be formed by a writing technique using the ultrashort pulse laser. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120327

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The nonlinear optical responses of laser-ablated Si nanoclusters were measured at &lgr;=532 nm.Re{&khgr;(3)}values as high as−(1.33±0.33)×10−3esu were measured for films that were only 200 nm thick. The response time for this nonlinearity was as short as 3.5±0.5 ns, limited by our laser pulse duration. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120328

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Europium activated yttrium oxide(Eu:Y2O3)phosphor films have been grownin situon (100) bare and diamond-coated silicon substrates using a pulsed laser deposition technique. Diamond-coated silicon substrates were prepared using hot filament chemical vapor deposition of diamond onto silicon. Photoluminescence brightness fromEu:Y2O3films grown at 700 °C on diamond-coated silicon substrates was about twice that of films on bare silicon, and reached 80&percent; of the brightness of powders. The higher brightness fromEu:Y2O3film on diamond-coated silicon substrates is attributed to reduced internal reflections from theEu:Y2O3film surface, which results from the roughness of the diamond layer. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120329

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

3- or 5-hydroxyflavone-metal complexes were synthesized and applied to organic light-emitting diodes (OLEDs) as an emitting material and an electron transport material. Whenbis(5-hydroxyflavonato)beryllium[Be(5Fla)2]was used as an emitting material, the OLED showed a luminance of1900 cd/m2with yellow. On the other hand, when used as an electron transport material in an organic three-layer cell, a high luminance of more than10 000 cd/m2was obtained. Furthermore, the turn-on voltage of the OLED could be lowered to 2.4 V and its lifetime was more than 1300 h.Be(5Fla)2was found to have a good electron transporting capability and good stability. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120330

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effect of transmission through a fiber Bragg grating on the relative intensity noise of semiconductor laser light is investigated. We first present a model of the grating as a linear frequency discriminator that exchanges correlated power between frequency noise and intensity noise caused by spontaneous emission. This correctly explains observed increases in intensity noise of up to 30 dB at low frequencies, obeying an inverse-square frequency dependence. Next, we show that there exist conditions under which a grating can reduce intensity noise and that these are determined by the phase relationship between correlated intensity and frequency fluctuations. Finally, we demonstrate a 2 dB reduction of intensity noise at frequencies up to 15 GHz, and present a numerical calculation based on the complex transmittance of the grating that correctly describes the effect of grating dispersion. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120331

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We show that the degradation of a nonencapsulated polymer-based light-emitting diode (LED) is accompanied by the appearance of strong fluctuations,—that is noise both in the radiance and in the film resistance. We demonstrate a correlation between the morphological changes which occur during the degradation process and the noise, suggesting that the sampling of noise during LED operation can be used as a very efficient tool to predict the approaching failure of LEDs in real-life applications. The morphological changes in LED degradation are essentially a two-stage process. First, there is formation of “bubbles” at the metal–polymer interface due to delamination of the polymer film from the metal surface. Second, carbonized areas in the form of “black spots” are formed. Accumulation of carbonized areas leads to short and/or open circuits and final LED failure. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120332

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have developed a technique to generate tunable multi-wavelength picosecond pulses using a self-seeded gain-switched laser diode. The external cavity allows simultaneous feedback of up to four wavelengths into the laser diode for mode selection. A tunable spectral spacing of about 20 nm among the wavelength channels can be obtained. The optimized output side-mode suppression is higher than 20 dB. Different channels in the output are separated temporally and can be individually accessed for modulation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120333

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The exciton states of GaAs coupled quantum wires are investigated by the measurement of photoluminescence excitation (PLE) in comparison with those of single quantum wires. In the PLE spectra of single quantum wires (wirethickness=4.5 nm), sharp exciton peaks of the first two heavy hole-like transitions are observed with large energy difference of 47 meV, while two adjacent exciton peaks with the small energy splitting of 24 meV are observed in the coupled quantum wires (wirethickness=5 nm,barrierthickness=3 nm). From the measurements of the barrier thickness dependence, these exciton states agree well with the coupled states of the quantum wires calculated by the finite element method. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120334

出版商:AIP    

年代:1997

数据来源: AIP