摘要:

The change in the second-order nonlinear susceptibility of an asymmetric quantum well (AQW) superlattice induced by ion beam-enhanced intermixing has been measured. The surface-emitted second-harmonic intensities radiated from implanted and masked areas of an AQW waveguide were measured and compared for incident wavelengths between&lgr;=1480and 1600 nm. Intermixing resulted in a 60 meV blueshift of the AQW band edge and a uniform suppression of the AQW second-order susceptibility, while the masked AQWs were unchanged. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121558

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We discuss the performance of a micromachined, photoconductive terahertz emitter that is fabricated on low-temperature-grown GaAs. The device is mounted on a pair of single-mode optical fibers that allows the source to be freely positionable. A strong radiation burst is emitted due to the large magnetic moment created by the electrode. The emitter’s small feature size of 300 &mgr;m by 300 &mgr;m with a photoconductive switch area of 30 &mgr;m by 30 &mgr;m suggests its application for terahertz, time-domain, near-field spectroscopy and imaging. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121559

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The piezoelectric effects on the optical gain of wurtzite GaN/AlGaN QW lasers taking into account the many-body effects are presented. The self-consistent model with piezoelectric field effect shows that band structures and optical gain are significantly affected by the piezoelectric field at relatively low carrier densities. The peak gain is redshifted and smaller when compared to the flat-band model without piezoelectric field effect. Only gain peaks corresponding to C1-HH1 and C1-LH1 transitions are observed in the investigated range and transitions for C1-HH2 and C1-LH2 are negligible due to the large subband energy spacing at low carrier densities and small matrix elements at high carrier densities. At high carrier densities, the self-consistent model shows band structures and optical properties similar to the flat-band model due to the screening effects. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121560

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report the growth of a four-period multiple quantum well (MQW) structure with 115-Å-thick,+1.65&percent;strained wells by metalorganic molecular beam epitaxy and its application to 2 &mgr;m wavelength lasers. Transmission electron microscopy and photoluminescence measurements reveal that the structural and optical properties of MQW are sensitive to the barrier strain: the values of barrier strain required for MQW with both flat barrier-well interfaces and strong photoluminescence fall within a small range from−0.17&percent;to+0.14&percent;.The double-crystal x-ray diffraction pattern of the MQW remains unchanged before and after annealing at 620 °C for 2.5 h. Buried heterostructure lasers fabricated using metalorganic vapor phase epitaxy regrowth have an emission wavelength of 2.07 &mgr;m under a continuous operation current of 120 mA at 55 °C. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121561

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The growth dynamics of UV induced IR absorption and related refractive index change in hydrogen loadedGeO2-doped fibers have been studied. We report a higher initial rate and strong saturation for Ge–OH generation compared with Si–OH formation under UV exposure. A close correlation was found between the Ge/Si–OH groups concentration and the induced index change as a function of the UV exposure time. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121562

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Emission characteristics of proton implanted vertical cavity surface emitting lasers have been studied by spectrally-resolved near-field scanning optical microscopy (NSOM). Measured spatial intensity distributions of individual transverse modes show a fundamental mode at threshold, and two double-lobed first-order modes excited around aperture edge above1.3×threshold injection current. The use of high spectral and spatial resolution NSOM enabled the detection of a local resonance wavelength dependence on position across the laser aperture; from these data, a lateral refractive index variation is calculated. As the injection current is increased, these index distributions are found to be consistent with the observed reduction of the spatial width of the intensity distribution and the increase in the spectral mode spacing. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121563

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have improved the optical characteristics of aluminum-coated fiber probes used in near-field scanning optical microscopy by milling with a focused ion beam. This treatment produces a flat-end face free of aluminum grains, containing a well-defined circularly-symmetric aperture with controllable diameter down to 20 nm. The polarization behavior of the tips is circularly symmetric with a polarization ratio exceeding 1:100. The improved imaging characteristics are demonstrated by measuring single molecule fluorescence. Count rates increase more than one order of magnitude over unmodified probes, and the molecule images map a spatial electric field distribution of the aperture in agreement with calculations. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121564

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

One of the factors limiting the sensitivity of wavelength modulation experiments is the fringing that is created by inadvertent multiple reflections between parallel optical surfaces in the apparatus. It is shown that the effects of this “e´taloning” can be countered by using detection harmonic orders greater than the second. A theoretical basis for the effect is presented and compared with experimental results obtained. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121565

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Optically induced refractive index patterns, which can be used for waveguides, were formed inSrxBa1−xNb2O6crystals using an erasable fixing mechanism, based on domains formation by the screening effect. The sign and strength of the refractive index change of the fixed waveguides was controllable by an applied electric field. Fixed patterns are shown to allow the storage of many spatially multiplexed holograms. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121566

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An inhomogeneously biased distributed feedback (DFB) laser diode (LD) with two electrodes switched its polarization mode by 3 mA change of the bias current, maintaining single longitudinal mode oscillation. In the active layer of the LD, 13 nm thick and 0.6&percent; tensile-strained InGaAs multiple quantum well (MQW) equalized the transverse electric and the transverse magnetic modal optical gain at 1.55 &mgr;m. With various grating pitches on the same MQW active layer, polarization switching DFB LDs were realized in the wavelength range as wide as 18 nm. The linewidth characteristics during the polarization switching were confirmed to be narrow due to the small switching current. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121567

出版商:AIP    

年代:1998

数据来源: AIP