Ga(As)Sb quantum dots (QDs) are epitaxially grown in AlGaAs/GaAs in the Stranski-Krastanov mode. In the recent past
we achieved Ga(As)Sb QDs in GaAs with an extremely high dot density of 9.8∙1010 cm-2 by optimization of growth temperature, Sb/Ga flux pressure ratio, and coverage. Additionally, the QD emission wavelength could be chosen precisely with these growth parameters in the range between 876 and 1035 nm. Here we report a photoluminescence (PL) intensity improvement for the case with AlGaAs barriers. Again growth parameters and layer composition are varied. The aluminium content is varied between 0 and 90%. Reflectance anisotropy spectroscopy (RAS) is used as insitu growth control to determine growth rate, layer thickness, and AlGaAs composition. Ga(As)Sb QDs, directly grown in AlxGa1-xAs emit no PL signal, even with a very low x ≈ 0.1. With additional around 10 nm thin GaAs intermediate layers between the Ga(As)Sb QDs and the AlGaAs barriers PL signals are detected. Samples with 4 QD layers and AlxGa1-xAs/GaAs barriers in between are grown. The thickness and composition of the barriers are changed. Depending on these values PL intensity is more than 4 times as high as in the case with simple GaAs barriers. With these results efficient Ga(As)Sb QD lasers are realized, so far only with pure GaAs barriers. Our index-guided broad area lasers operate continuous-wave (cw) @ 90 K, emit optical powers of more than 2∙50 mW and show a differential quantum efficiency of 54% with a threshold current density of 528 A/cm2.
A dynamic microfluidic iris is realized. Light attenuation is achieved by absorption of an opaque liquid (e.g. black ink).
The adjustment of the iris diameter is achieved by fluid displacement via a transparent elastomer (silicone) half-sphere.
This silicone calotte is hydraulically pressed against a polymethylmethacrylate (PMMA) substrate as the bottom
window, such that the opaque liquid is squeezed away, this way opening the iris. With this approach a dynamic range of
more than 60 dB can be achieved with response times in the ms to s regime.
The design allows the realization of a single iris as well as an iris array. So far the master for the molded silicone
structure was fabricated by precision mechanics. The aperture diameter was changed continuously from 0 to 8 mm for a
single iris and 0 to 4 mm in case of a 3 x 3 iris array.
Moreover, an iris array was combined with a PMMA lens array into a compact module, the distance of both arrays
equaling the focal length of the lenses. This way e.g. spatial frequency filter arrays can be realized.
The possibility to extend the iris array concept to an array with many elements is demonstrated. Such arrays could be
applied e.g. in light-field cameras.