Optical resolution beyond the diffraction limit can be achieved by use of a metallic nanoaperture in a near-field optical system. Conventional nanoapertures have very low power throughput. Using a numerical finite-difference time domain method, we discovered a unique C-shaped aperture that provides approximately 3 orders of magnitude more power throughput than a conventional square aperture with a similar near-field spot size of approximately 0.1 lambda. Microwave experiments at 6 GHz quantitatively confirmed the simulated transmission enhancement. The high transmission of the C-aperture--or one of the related shapes--is linked to both a propagation mode in the aperture and local surface plasmons.
Impurity-free selective layer disordering, utilizing Si3N4 masking stripes and SiO2 defect (vacancy) sources, is used to realize room-temperature continuous AlxGa1−xAs-GaAs quantum well heterostructure lasers.
The temperature dependence of threshold current and quantum efficiFncy for Ga,In, -,P (x = 0.4, 0.6; 1 = 680, 633 nm) single 80 A quantum-well lasers is compared and analyzed using a model for the electron leakage current. This model fits the experimental data well, correctly describing the rapid increase in threshold and drop in quantum efficiency as temperature increases. Also it indicates that the drift (rather than diffusion) component of the electron leakage current is dominant, because of the poor p-type conductivity in AIGaInP.
We report a comparison between measured and calculated far field data for an optically pumped In 0.15 Ga 0.85 N/In 0.05 Ga 0.95 N multiquantum well laser structure with AlGaN cladding layers. Optical pumping of the semiconductor device was performed with a pulsed 337 nm N 2 laser, whose beam was focused to a narrow stripe. A thin upper cladding layer allowed efficient pumping of the In 0.15 Ga 0.85 N/In 0.05 Ga 0.95 N laser structure. Despite high distributed cavity losses of at least 30 cm Ϫ1 , and although gain occurred in the small active region only, the seventh order transverse mode was supported in a waveguide formed by the entire 5-m-thick epitaxial layer structure. Excellent agreement is demonstrated between measured and calculated far field patterns of the lasing mode.There is considerable interest in applications of blue semiconductor lasers fabricated in the III-V nitrides. The use of compact short wavelength light sources will improve the resolution of scanners and printers as well as increase the storage density of optical disks. High quality GaN films and AlGaInN heterostructures can be grown epitaxially in organometallic vapor phase epitaxy ͑OMVPE͒ reactors as was described earlier. [1][2][3][4] Prior to the fabrication of injection lasers it is possible to achieve stimulated light emission of the grown material by optical pumping. [5][6][7][8] We report in this letter the optical excitation of a higher order lasing mode which propagates in a multimode waveguide formed by the entire 5-m-thick epitaxial layer stack with the sapphire substrate providing the lower cladding layer. Since observations of a threshold in the output versus pump intensity characteristic, TE polarization of the emission, and linewidth narrowing above threshold are necessary but not sufficient conditions to conclude lasing, we include here for the first time, to the best of our knowledge, a comprehensive investigation of the transverse far field pattern to demonstrate lasing under photopumping conditions. Similar measurements on GaAs/AlGaAs injection lasers have been made earlier, but their main goal was to give a proof of existence of Hermite-Gaussian mode patterns in semiconductor light sources. 9,10 A near field calculation using the effective index method reveals that the seventh order mode of this thick multimode waveguide has maximum overlap with the multiple quantum well ͑MQW͒ structure in the center of the active region. Further calculations show an excellent agreement of the measured and the calculated far field pattern for this mode.For these experiments, we used C-face sapphire (Al 2 O 3 ) wafers as the substrate material. Growth was performed in an OMVPE system. On the sapphire, we grew 4 m of GaN, followed by a 500-nm-thick Al 0.1 Ga 0.9 N lower cladding layer, a 240-nm-thick GaN/InGaN waveguide, and a 50-nm-thick Al 0.1 Ga 0.9 N upper cladding layer. Because of the relatively low carrier diffusion length in nitride films, the thin upper cladding layer was required for optical pumping of the MQWs. The active regi...
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