摘要:

This letter shows theoretically and experimentally that Fresnel end reflection of the waveguide under test degrades the sensitivity of low coherence optical time domain reflectometry (OTDR). Optical mixing of end reflection and reference light in the OTDR produces the phase noise in proportion to end reflectivity. With the balanced detection technique, the excess photon noise is subdued and the phase noise becomes the dominant source of sensitivity degradation. At 3.2% end reflection and 300 &mgr;A mean photocurrent, the noise floor due to the phase noise is −138 dB/Hz. By reducing the fiber end reflection with matching oil, a shot‐noise limited sensitivity of −140 dB at a 3 Hz bandwidth has been demonstrated at submillimeter resolution.

ISSN:0003-6951    

DOI:10.1063/1.105981

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Very low threshold current densities of 200 and 400 A/cm2were obtained in 1.5 &mgr;m GaInAs/AlGaInAs tensile and compressive strained‐layer quantum well laser diodes (SL‐QW LDs), grown by organometallic chemical vapor deposition, with continuously graded‐index separate‐confinement‐heterostructure. The differential quantum efficiency of SL‐QW LDs showed less sensitive to temperature in contrast to that of a lattice matched QW LD. This is attributed to the decrease of intervalence band absorption due to the strain‐induced reduction in the valence band density of state. The polarization of output power for a tensile SL‐QW LD showed transverse magnetic (TM) mode, while that for a lattice matched and a compressive SL‐QW LDs showed transverse electric (TE) mode.

ISSN:0003-6951    

DOI:10.1063/1.105982

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We show that modulation‐type instability can occur in the normal dispersion regime of a dielectric medium for the case of a relaxing self‐focusing nonlinearity. This instability leads to the generation of pulse trains with almost no pedestal when periodic boundary conditions are applied.

ISSN:0003-6951    

DOI:10.1063/1.105983

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report measurements of intensity as a function of both time and frequency for frequency modulation and switching of a tunable semiconductor laser. Because of the uncertainty principle limitations, the measured time‐frequency signal can have a complex structure and does not show the simple‐minded picture of a laser spectrum whose center frequency varies in time. The observations are explained by a theory of the time‐dependent spectral measurements, well known in the field of speech analysis. We discuss implications for channel switching speed and channel interference in switched, frequency‐multiplexed optical networks.

ISSN:0003-6951    

DOI:10.1063/1.105984

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Permanent modifications of the second‐order nonlinear susceptibility &khgr;(2)(−2&ohgr;;&ohgr;,&ohgr;) of certain Langmuir–Blodgett (LB) films can be induced photochemically by local irradiation with UV laser light, with the spatial resolution limited only by the laser spot size. In a LB film consisting of alternating monolayers of poly[N‐(p‐perfluorodecylsulfonylphenyl)‐L‐prolinol acrylate] and a ‘‘buffer’’ polymer, the kinetics of the laser bleaching process, as studied by optical second‐harmonic generation, is found to be first order. The generation of a ‘‘&khgr;(2)‐grating’’ in the LB film is also demonstrated.

ISSN:0003-6951    

DOI:10.1063/1.105985

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Intense emission of the TE12mode has been detected in an experiment based on the cyclotron resonance maser mechanism with nonadiabatic electrostatic pumping of an electron beam. The pitch‐ratio &agr; of beam electrons has been found experimentally and estimated from a computer simulation. Both results are in good agreement with each other.  

ISSN:0003-6951    

DOI:10.1063/1.105954

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The angular dependence of the second‐harmonic (SH) generation efficiency at the copper and aluminum surfaces has been measured. In aluminum the bulk and the parallel surface nonlinear polarization gives the main contribution to the SH generation. In copper the normal surface nonlinear polarization contributes significantly to the SH generation.

ISSN:0003-6951    

DOI:10.1063/1.105959

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Latching optical switches and cascadable optical logic gatesandandorare demonstrated by the monolithic integration of a vertical‐cavity surface‐emitting laser with heterojunction photothyristors. Excellent optical switching characteristics, including low switching power (tens of nW), high optical gain (≳104), and a large on/off ratio, have been achieved.

ISSN:0003-6951    

DOI:10.1063/1.105934

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The realignment by rapid thermal annealing of polycrystalline silicon layers deposited onto ⟨100⟩ Si substrates can occur either through the planar movement of the interface towards the surface or through the lateral growth of columnar epitaxial islands. An anneal at 1075 °C for 15 s, followed by As implantation, is shown to cause planar growth even at subsequent anneal temperatures as low as 900 °C. In contrast, the direct annealing of As implanted samples induces columnar realignment. Further, the As redistribution throughout the polycrystalline layers and its diffusion in the crystalline substrate is considerably reduced in the case of the double step annealing. The different regrowth modes are related to the morphology of the interfacial oxide layer and to the microcrystalline structure of the polycrystalline layers during the initial stages of the realignment process.

ISSN:0003-6951    

DOI:10.1063/1.105935

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A new kind of ultrafine amorphous particles Fe82P11B7have been successfully prepared by the reaction of Fe(III) chloride, sodium hypophosphite and potassium borohydride in aqueous solution. X‐ray diffraction and Mo¨ssbauer spectroscopy confirmed the amorphous structure of the particles and scanning electron microscopy showed that the particles are nearly spherical with the diameters from 150 to 350 nm. The structure relaxation and crystallization of the amorphous particles were also studied by Mo¨ssbauer spectroscopy. It is found that the particles began to crystallize when annealed at 573 K, below which, no crystalline phases were formed, but the amorphous structure significantly varied. The particles crystallized to form &agr;‐Fe and Fe3(P0.6B0.4) completely when annealed at 673 and 773 K.

ISSN:0003-6951    

DOI:10.1063/1.105936

出版商:AIP    

年代:1991

数据来源: AIP