摘要:

A new numerical method for analyzing birefringence and dispersion characteristics of birefringent optical fibers is presented. A major advantage of the method, based on the solution of full‐vectorial Maxwell equations, is its high accuracy no matter how great the geometrical anisotropy of the optical fiber. To verify the reliability of our numerical procedure, the modal birefringence and the form‐induced polarization mode dispersion in elliptical core fibers with different eccentricities are investigated and their values compared with some theoretical and experimental results. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359369

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Charge carrier competition between the gratings produced in degenerate four‐wave mixing in bismuth silicon oxide reduces steady‐state diffraction efficiency, suppresses several processes of transient diffraction efficiency, and changes the concavity of reflection grating development. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359357

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A 1.3 &mgr;m modulator using light‐hole–to‐electron interband Stark shift in the lattice‐matched AlInAs/GaInAs coupled quantum wells (CQWs) is investigated theoretically. The operation of this device is based on the lowest‐energy absorption resonance corresponding to the first light‐hole–to–electron transition (ELh1→Ee1). The resonant nature of this process results in a sharp absorption peak when the incident photon energy is equal to the energy‐level separation. This device utilizes the significant enhancement of the Stark effect on the electronic states and the strong field‐dependence transition dipole moments. Under an applied electric field, the energy spacing betweenELh1andEe1changes due to the Stark shift. The contrast ratio can be improved from 8:1 for the symmetric CQW to as high as 20:1 for the proposed asymmetric CQW structure. These contrast ratios are achieved by varying the applied electric field in the 0–70 kV/cm range. This large variation of optical absorption at 1.3 &mgr;m is obtained both by the enhanced Stark shift and by varying the overlap between the hole and electron envelope wave functions with an applied electric field and Stark effect for the proposed AlInAs/GaInAs CQW system. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359377

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The concept of characteristic thermal dimension was recently introduced to predict the behavior at high frequencies of the bulk modulus of fluids saturating a porous frame. This thermal dimension is closely related to the specific surface of the solid porous frame. It is shown that the standard Brunauer, Emmett, and Teller method (BET) of measuring the specific surface and acoustical measurement of the bulk modulus are in good agreement, and that the viscous dimension can be evaluated unambiguously from the BET method plus an acoustical measurement. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359366

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The requirements for heteroepitaxial growth of Sb on both GaSb and GaAs, and the subsequent growth of GaSb on Sb, using molecular‐beam epitaxy are described. These systems serve as examples of the heteroepitaxy of group‐V elements with III‐V compounds, i.e., between materials utilizing different bonding and possessing different electronic properties. The quality of the films was determined using high‐resolution four‐circle x‐ray diffraction, and comparisons were made between different structures. GaSb was found to grow (111) oriented on Sb (111) with an inverted stacking sequence. A simple epitaxial model is proposed to explain this. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359373

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We developed a new scanning tunneling microscopy technique to measure the surface potential. The new method exploits the tunneling voltage dependence of the tip‐sample separation. The indirect measurement of the potential together with a differential measurement technique makes the new potentiometry insensitive to errors of the electronic setup and provides submicrovolt sensitivity limited by approximately thermal noise of the tunneling resistance. We illustrate the new technique by basic measurements performed under ultrahigh‐vacuum conditions. In addition we present the coherence of tunneling current fluctuations and potential fluctuations which underlines the quality of the new technique: the coherence differs significantly from unity. We conclude that the tunneling resistance does not have thermal voltage fluctuations predicted by Nyquist’s formula. Possible sources of residual voltage fluctuations such as single electron tunneling effects are discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359390

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Anomalous x‐ray diffuse scattering is used to study the short‐range order (SRO) and lattice distortions in the electron‐type superconductor, Nd1.85Ce0.15CuO4−y. The intensity measurements were made at two energies below the Ce LIIIabsorption edge; the difference data greatly simplified the analysis to involve only atom pairs including Ce. The data sets were analyzed using a kinematic diffraction equation expanded up to the second order in atomic displacements. The fitted SRO parameters indicate the formation of Ce‐Ce atom pairs along the ⟨001⟩ directions. For superconductivity to occur in this and other doped cuprate compounds, the size of the dopant free regions in the basal plane may have to exceed the superconducting coherence length. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359328

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A low‐temperature infrared‐absorption study has been performed to investigate the annealing behavior of the carbon‐oxygen complexes causing the peaks at 1104 cm−1(C‐OAcomplex) and 1108 cm−1(C‐ODcomplex). Upon annealing, the concentrations of the C‐OAand C‐ODcomplexes quickly reach the quasithermal‐equilibrium values described by the mass‐action law. The obtained formulas of this mass‐action law indicate that both of these two complexes involve a carbon atom and an oxygen atom. For the annealing temperatures higher than 800 °C, the quasithermal‐equilibrium concentration of the C‐OAcomplex increases with increasing temperature. A hypothetical explanation is proposed for this unusual temperature dependence. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359344

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Detailed investigations of the microstructure and polycrystalline epitaxy of CoNiCr/Cr bilayer films have been carried out using various techniques of transmission electron microscopy. The average grain size for both the Cr and CoNiCr layers was about 510 A˚ although there is a great difference in their morphology. Analysis of the discontinuous ring (arced) diffraction patterns of the layers showed that the Cr underlayer is strongly [001] textured and the CoNiCr layer is weakly [112¯0] textured. The angular distribution of the Cr underlayer [001] texture axis was determined to be 6.7° and the ratio of the number of [001] textured grains to that of the randomly oriented grains was estimated to be 3:7 using dark‐field imaging techniques. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359353

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report here the Raman scattering studies of modifications in the structural disorder due to fluorine incorporation in the hydrogenated amorphous silicon‐carbon (a‐Si1−xCx:H) alloys. The structural disorder in the unfluorinateda‐Si1−xCx:H alloys has been observed to increase continuously with the increasing carbon content, whereas the incorporation of fluorine appears to substantially suppress disordering effects of carbon, irrespective of its concentration in the alloy. Additional support for this suppression of disorder is sought from the enhancement of optical band gap after fluorine incorporation in these alloys. The fluorine‐induced suppression of disorder is attributed to the increase in the fraction ofsp3bonded carbon in the fluorinated alloys compared to that of the unfluorinated alloys. The fluorine as well as hydrogen appear to have a preferential attachment with the carbon atoms that tend to form higher hydride and fluoride species which in turn constrain the carbon atoms to formsp3hybridized C‐C or Si‐C bonding in the alloys. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359354

出版商:AIP    

年代:1995

数据来源: AIP