摘要:

Experimental data are presented to show that Ge(1) and Ge(2) centers are induced by trapping photoinduced electrons from the conduction band, in agreement with our previous proposal that both are trapped electron centers. The spacing (&Lgr;) dependence of ultraviolet (UV) light bleaching of the pre-existingGe E′centers illustrates that the electron diffusion length is greater than &Lgr; of the spatially modulated UV light used in the fabrication of fiber Bragg gratings (FBGs) with Bragg wavelengths⩽1.5 &mgr;m(short period grating) for laser powers as low as25 mJ/cm2.The Ge(1) and Ge(2) centers are uniformly induced by the spatially modulated UV light and therefore contribute to the uniform component of the index structure of FBGs.

ISSN:0003-6951    

DOI:10.1063/1.121678

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This letter discusses the design and the realization of asymmetric Fabry–Perot modulators with InP/InGaAsP distributed Bragg reflectors and 80 AlInGaAs quantum wells. We demonstrate two types of modulators utilizing two different top reflectors: an InP to air interface and aSi/SiO2/Sicoating. The first modulator showed a monotonic reduction in the reflectivity as the bias voltage increased, and achieved a 2.2 dB insertion loss and a 15 dB contrast ratio at the resonant wavelength. The second modulator showed an initial reduction and then an increase in the reflectivity as the bias changed from 0 to−10 V.The chirp calculation based on the measured data reveals that the second modulator exhibits two distinct positive and negative chirp characteristics. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121612

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Performance of optical interconnects using volume holographic gratings and substrate-guided waves is subject to source wavelength detuning which originates from laser chirping and operating temperature changes. In this letter, we characterize and measure the dispersion of commonly used surface-normal volume holographic gratings. Dispersion characteristics of a 20 &mgr;m thick photopolymer volume holographic grating are evaluated. A dispersion correction method is demonstrated to provide a dispersion-free surface-normal optical interconnect using two dispersion-compensated volume holographic gratings and substrate-guided waves which automatically compensate the dispersion that results from detuning over a 5.7 nm bandwidth. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121613

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electrothermal poling of soft glasses (soda lime and borosilicate glass) at relatively high currents led to the creation of a second-order optical nonlinearity. The second-harmonic generation efficiency decays in time, and the decay rate can be accelerated by exposure to intense infrared radiation. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121614

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An analysis of the nonlinear distributed-feedback (DFB) laser action is presented. A set of nonlinear coupled-power equations is derived. A general condition for a nonlinear DFB laser with reduced spatial hole burning (SHB) is obtained. It is shown that the elimination of SHB in DFB lasers can be achieved by introducing properly-chosen variations of the coupling strength along the longitudinal direction; a novel complex-coupling AR-coated DFB laser diode is proposed as a result. It is also shown that the optical nonlinearity must be considered for the design of high-power laser structures with reduced SHB. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121615

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on the use of an epoxy based chemically amplified resist, to produce x-ray images of living biological specimens, exposed with laser plasma generated soft x rays, in the water window (2.3–4.4 nm). The photoresist response was at least two orders of magnitude “faster” than polymethyl methacrylate, the standard resist used so far in soft x-ray contact microscopy. Atomic force and scanning electron microscopy of the biological specimen images, recorded in the resist, clearly showed the flagella of the motile green alga, chlamydomonas, suggesting a lateral resolution better than 150 nm. The resist was also capable of providing height features, as small as 20 nm, in atomic force microscope depth profiles and discriminating the flagella intersection areas. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121616

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Spectroscopic ellipsometry (SE) has been used to determine the complex pseudo dielectric functions,&egr;1(E)+i&egr;2(E),of ZnO films on (0001)Al2O3substrates over the spectral range of 1.33 and 4.96 eV at room temperature. The SE measurements are carried out withE⊥cat angles of incidence of 60° and 65° with respect to the surface normal. Below the band gap, the refractive indexnis found to follow the first order Sellmeir dispersion relationshipn2(&lgr;)=1+1.881&lgr;2/(&lgr;2−0.05382).A free excitonic structure located at the band edge of 3.32 eV is clearly observed in the pseudo absorption spectrum. Elliott expression with Lorentzian broadening is used to model the pseudo absorption coefficient above the band edge. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121617

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Thirty one layerTiO2/SiO2optical filters with graded refractive index profiles were fabricated by helicon plasma sputtering at room temperature. Multilayer films were deposited on glass (BK7) and Si (100) substrates simultaneously and sequentially. The measured transmittance spectrum exhibited a reflectance of 99.8&percent; at a central wavelength of 730 nm and high transmittance over the wavelength region outside of the reflected band as a result of the suppression of the sidelobes. The experimental transmittance spectrum corresponded almost completely with that calculated based on the optical multilayer film theory and using the measured refractive indices ofTiO2,SiO2andTiO2–SiO2composite films. Transmission electron microscopic observations confirmed the expected microstructure of the filter. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121618

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have observed progressive damage due to reabsorption of stimulated emission in optically pumped laser-quality GaInN–GaN multiple quantum wells. The degradation occurred on a time scale consistent with the lifetime of electrically pumped lasers incorporating the same active region, suggesting that the failure mechanism was in part catastrophic optical damage, and not just heating in thepcontact andpcladding as is often assumed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121619

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Room-temperature ultraviolet (UV) laser emission of ZnO microcrystallite thin films is reported. The hexagonal ZnO microcrystallites are grown by laser molecular beam epitaxy. They are self-assembled and parallelly arrayed on sapphire substrates. The facets of the hexagons form natural Fabry–Pe´rot lasing cavities. The optical gain for the room-temperature UV stimulated emission is of an excitonic nature and has a peak value an order of magnitude larger than that of bulk ZnO crystal. The observation of room-temperature UV lasing from the ordered, nano-sized ZnO crystals represents an important step towards the development of nanometer photoelectronics. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121620

出版商:AIP    

年代:1998

数据来源: AIP