We demonstrated a novel two-dimensional photonic crystal (PC) based Symmetric Mach Zehnder type all-optical switch (PC-SMZ) with InAs quantum dots (QDs) acting as a nonlinear phase-shift source. The 600- ?m-long PC-SMZ having integrated wavelength-selective PC-based directional couplers and other PC components exhibited a 15-ps-wide switching-window with 2-ps rise/fall time at a wavelength of 1.3 ?m. Nonlinear optical phase shift in the 500-?m-long straight PC waveguide was also achieved at sufficiently low optical-energy (e.g., ??phase shift at ~100-fJ control-pulse energy) due to the small saturation energy density of the QDs, which is enhanced in the PC waveguide, without using conventional measures such as SOAs with current-injected gain. The results pave the way to novel PC- and QD-based photonic integrated circuits including multiple PC-SMZs and other novel functional devices.
The resonant tunneling of electrons through a 20 nm scale InAs quantum dot bound by a pair of very thin AlAs barriers is studied. A well-resolved composite peak resulting from the ground 1s states was observed at 4.2 K in current–voltage characteristics. By investigating the effects of inplane magnetic fields, the shape of the wave function and the spatial extent of the first two electronic states are clarified.
Mechanisms of molecular beam epitaxy have been investigated for GaAs and AlAs by growing and analyzing the shapes of facet structures consisting of an (001) top surface and two (111)B side surfaces. It is found that all of the Ga flux on the three facet planes is incorporated into the film, but the growth rates on (111)B and (001) depend strongly on the As flux and are mainly determined by the diffusion of Ga ad-atoms between the two planes. In contrast, the diffusion of Al is found to be almost negligible, irrespective of the As flux. By analyzing the shape of the facet, the diffusion length, λ, of Ga on a (001) surface is estimated to be about 1 μm at 580 °C, while that of Al is about 0.02 μm. On (111)B, λ of Ga is found to be several μms. The reflectivity of diffusing Ga atoms is found to be far less than 1 for the (001)-(111)B boundary, and almost unity at facet boundaries where the (111)B side surfaces are bound by the (11̄0) side walls.
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