摘要:

We report the results of a study of spatially resolved surface-emitted stimulated emission in GaN epilayer samples under conditions of strong optical pumping. We observe that even at excitation powers near the damage threshold, no surface-emitted stimulated emission occurs from samples with a high quality GaN epilayer. In parts of the samples with inferior surface quality, we show that stimulated emission comes from cracks, burned spots, and other imperfections, and is due to the scattering of a photon flux propagating parallel to the surface. Our results suggest that these defects are effective scattering centers and can severely affect the accuracy of optical gain measurements. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119627

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Unprecedentedly high reflectivity distributed Bragg reflectors consisting of fluorocarbon polymer(CFx)and high refractive index inorganic oxide multilayers have been fabricated by means of assisted ion-beam sputtering at room temperature. Multilayer stacks consisting of aCFx/TiOxandCFx/HfOxpairs exhibit reflectivities larger than 98&percent; in the infrared and ultraviolet spectral region, respectively. The superior wide tunability and the high efficiency, with respect to inorganic–inorganic multilayers is due to the exceptionally low refractive index of the fluorcarbon polymer(n≃1.35)on a very large spectral region (300–2000 nm). ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119628

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Multiple quantum well InAs/GaSb laser heterostructures with type III (type II broken gap) band alignment in the active region have been grown by molecular beam epitaxy. Intense electroluminescence was observed at room temperature (RT) with peak emission wavelengths in the range 1.95–3.4 &mgr;m. RT lasing has been achieved at 1.98 and 2.32 &mgr;m for the structures with 6 and 12 Å thick InAs quantum wells, respectively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119629

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We describe an experimental setup, which allows assessing the optical properties of two-dimensional photonic crystals combined with a waveguide geometry, and etched into a light-emitting (GaAs/InGaAs) semiconductor. By means of a guiding layer, the spontaneous emission of the material is used as a built-in source to probe the properties of the etched microstructure, conveniently compared to the usual measurement schemes. We show polarized transmission and coefficients largely depending on the photonic crystal orientation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119630

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report that the 780 nm quantum well vertical-cavity surface-emitting lasers (VCSELs) grown on a 2° off misoriented (001) substrate toward (111)A exhibit a high polarization suppression ratio over a few hundred. The main polarization is always along the[−110]direction for all the lasers over the entire operating currents. To understand the physical origin of this polarization selectivity, the gain/loss difference between two competing polarization modes in VCSELs is investigated by measuring the subthreshold spectral linewidth. The obtained modal gain/loss difference is about3.0 cm−1,which is sufficiently large for polarization stabilization and amounts to 4&percent; of the threshold modal gain. Comparison with the subthreshold measurement and previous theoretical work shows significant discrepancy, which implies the possibility of other polarization selection mechanisms inducing such large gain/loss differences in 780 nm quantum wells grown on a misoriented substrate. In addition, it is found that the 780 nm VCSEL made of a bulk active medium grown on a misoriented substrate also shows a high polarization selectivity as quantum well lasers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119631

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The distribution of a confined optical field within a microcavity was determined using a thin layer of the fluorescent polymer PPV as a probe of the local-field amplitude. It is shown that the photoluminescence emission intensity from the cavity is a function of the axial position of the polymer, and confirms that a microcavity can be used to control spontaneous emission. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119632

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An integrated all-optical switch based on a high-Qnonlinear cylindrical microcavity resonator is proposed. The switch consists of single mode planar waveguides that allow coupling light in and out to a microresonator, exhibiting whispering gallery modes. Due to the highQfactor and the small dimensions, fast switching at low power is feasible for devices based on presently available nonlinear polymers as the active material. In this approach, the transmission of an integrated optical waveguide close to a microcavity has been measured and related to the resonances of the cylindrical microcavity. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119633

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A transverse electric (TE) mode selective polymer waveguide was fabricated by a photobleaching process using a urethane–urea copolymer. The output power of the TE modes through the waveguide was higher than that of the transverse magnetic (TM) modes, when the TE and TM modes were excited equally, the TE mode to TM mode extinction ratio being 27 dB. Mode selectivity was explained by the following relation of the refractive index: the refractive index for the TE modes in the core region was higher than that in the cladding region, while the refractive index for the TM modes in the core was lower than that in the cladding. This relation was attained by the photoinduced change in birefringence of the polymer layer. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.119634

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A widely tunable THz wave has been parametrically generated and reported recently by us utilizing aLiNbO3crystal with a monolithic grating coupler under a noncollinear phase matching condition. However, the output direction of the THz wave is strongly dependent on the generated frequency due to the nature of noncollinear phase matching, as well as the grating coupler. In this letter, a novel method for THz coupling is proposed using a low dispersion prism to eliminate almost completely the THz beam deflection for the entire tuning range. The unidirectional THz wave radiation was confirmed theoretically and experimentally for the range of 1–2 THz. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119635

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ion-exchange processes in potassium titanyl phosphate(KTiOPO4or KTP) single crystal immersed in Rb, Rb–Ba, Rb–Sr nitrate molten solutions have been investigated by using Rutherford backscattering depth-profile analysis. The depth to which Rb-ion exchange occurred in KTP was found to be sensitive to the presence of as little as 0.1&percent; of a Ba impurity in a molten solution of rubidium nitrate. The addition of impurities such as Ba significantly increased the ion-exchange depth of Rb in KTP, and the Rb distribution after ion exchange. Using pureRbNO3,however, the depth of the Rb ion exchange was relatively shallow, and the Rb surface concentration was measurably greater at the minus than at the plus polar-axis faces of the crystal. These findings are relevant to the application of ion-exchange techniques to the fabrication of optical waveguides on KTP substrates. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119636

出版商:AIP    

年代:1997

数据来源: AIP