摘要:

The fundamental limitations for all‐optical switching in a nonlinear directional coupler due to the saturation of the nonlinearity have been obtained by solving analytically the nonlinear coupled‐mode equations. We found that there is a minimum value required for the saturation index change to obtain efficient switching, and that the number of powers at which switching occurs at one beat length can double.

ISSN:0003-6951    

DOI:10.1063/1.98476

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Optical channel waveguides have been fabricated into integrated circuit lithography mask plates by silver‐sodium ion exchange. The process combines the advantages of Ag thin‐film ion sources and the accurate and reliable patterning of chromium films on mask plates. The process is potentially suitable for cheap mass production, since no lithography is needed during the actual waveguide fabrication. The tailoring of waveguide cross sections by modifying the electric field distribution inside the glass is also presented.

ISSN:0003-6951    

DOI:10.1063/1.98448

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We report observation of a rotation in the polarization of the two photorefractive recording beams in GaAs for a configuration with the internally generated space‐charge field along the ⟨110⟩ crystallographic orientation. This rotation is a result of simultaneous constructive and destructive beam coupling in each beam for the optical electric field components along the two electro‐optically induced principal dielectric axes of the crystal. By turning one of the beams on and off, the intensity of the other beam after the crystal and a polarization analyzer can be modulated by as much as 500%. This result is of particular importance for optical information processing applications.

ISSN:0003-6951    

DOI:10.1063/1.98449

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Spectral hole burning in semiconductor lasers manifests as a nonlinear suppression of the mode gain by a few percent. In the presence of a probe wave, the same mechanism can lead to highly nondegenerate four‐wave mixing (NDFWM) by creating the dynamic gain and index gratings at the beat frequency of the pump and probe waves. Since the grating efficiency is governed by the intraband relaxation time (typically <1 ps), significant NDFWM can occur even for a pump‐probe detuning ∼100 GHz. We present the results for the conjugate reflectivity and the probe transmittivity when an InGaAsP laser is used as a traveling‐wave amplifier.

ISSN:0003-6951    

DOI:10.1063/1.98450

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We report a new tip for scanning tunneling microscopy and a tip repair procedure that allows one to reproducibly obtain atomic images of highly oriented pyrolytic graphite with previously inoperable tips. The tips are shown to be relatively oxide‐free and highly resistant to oxidation. The tips are fabricated with graphite by two distinct methods.

ISSN:0003-6951    

DOI:10.1063/1.98451

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Tantalum silicide deposited directly on monocrystalline silicon substrates and annealed at 950 °C causes enhanced diffusion of both boron and antimony in buried layers. The effect is taken as evidence of vacancy supersaturation, since it is known that antimony diffuses in silicon by an almost entirely vacancy mechanism. It also indicates a substantial vacancy component in boron diffusion, at least at 950 °C, or lower. The simultaneous occurrence of boron and antimony enhanced diffusion contrasts with the nitridation effect on diffusion previously reported. That the enhanced diffusion occurred in buried layers excludes the snow‐plow mechanism. The Si:Ta ratio of the sputter‐deposited tantalum silicide is slightly less than 2. The interpretation is that further silicidation generates vacancies by removing silicon atoms from the silicon substrate. Enhanced diffusion was not detectable when there was a 150‐nm intervening layer of polycrystalline silicon film between the silicide and the monocrystalline silicon substrate, indicating that polycrystalline silicon is an effective sink for excess vacancies, perhaps more than it is for excess interstitials.

ISSN:0003-6951    

DOI:10.1063/1.98452

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Epitaxial YSi2−xfilms have been fabricated. The smooth 430‐A˚‐thick silicide films on Si (111) substrates were characterized by a Rutherford backscattering minimum channeling yield &khgr;min=8%, establishing YSi2−xas one of the best known epitaxial silicides. Results of electrical measurements are also presented.

ISSN:0003-6951    

DOI:10.1063/1.98453

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The segregation and diffusion of Au are examined during ion‐beam‐induced solid phase epitaxial crystallization of Au‐implanted amorphous silicon layers. Epitaxy was induced at temperatures as low as 220 °C by irradiation with 1.5 MeV Ar ions. At these temperatures Au is segregated to form a narrow layer at the moving crystal/amorphous interface. The size of the segregated layer depends on the velocity of the interface compared to the Au diffusivity in amorphous Si. The growth rate for ion‐beam‐induced epitaxy is found to be independent of Au concentration and near‐complete epitaxial crystallization of the amorphous layers can be achieved, even for Au concentrations ∼2 at. %.

ISSN:0003-6951    

DOI:10.1063/1.98454

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The formation of a polycrystalline solid compact, by fusing an initially porous aggregate of diamond crystals under dynamic shock pressure (7.5–18 GPa), is shown to depend critically on the size of the initial crystals. Porous aggregates of 100–150 &mgr;m diameter crystals upon shock compaction produced compacts. These exhibited pronounced fracturing of the individual crystals and showed no evidence of fusion. Aggregates consisting of ultrafine crystals (<5 &mgr;m) also exhibited minimal consolidation. However, samples composed of crystals in the range 4–8 &mgr;m produced strong fused compacts of polycrystalline diamond. A model calculation indicates that at 10 GPa less than 0.07 mass fraction of the diamond powder can be melted and this molten material is quenched in 0.8 ns for 8‐&mgr;m‐diam crystals.

ISSN:0003-6951    

DOI:10.1063/1.98427

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A graded gap quantum well structure, where the band gap is linearly changing along the growth direction, is proposed for the enhancement of quantum confined Stark effect. Theoretical calculations show that the ground‐state exciton peak energy shifts by a larger amount than in a usual square‐shaped quantum well under an applied electric field. The wave function modifications in this quantum well result in a smaller decrease of the exciton oscillator strength, according to the electric field applied. These effects reveal the possibility of achieving high‐performance optical modulators or other devices which utilize the quantum confined Stark effect.

ISSN:0003-6951    

DOI:10.1063/1.98428

出版商:AIP    

年代:1987

数据来源: AIP