We study the effect of an external biaxial stress on the light emission of single $\mathrm{InGaAs}/\mathrm{GaAs}(001)$ quantum dots placed onto piezoelectric actuators. With increasing compression, the emission blueshifts and the binding energies of the positive trion ($X^{+}$) and biexciton ($XX$) relative to the neutral exciton ($X$) show a monotonic increase. This phenomenon is mainly ascribed to changes in electron and hole localization and it provides a robust method to achieve color coincidence in the emission of $X$ and $XX$, which is a prerequisite for the possible generation of entangled photon pairs via the recently proposed “time reordering” scheme.

We demonstrate pronounced single-photon emission from InAs/AlGaInAs/InP quantum dots (QDs) at wavelengths above 1.5 μm that are compatible with standard long-distance fiber communication. The QDs are grown by molecular beam epitaxy on distributed Bragg reflectors. A low QD density of about 5 × 10⁸ cm⁻² was obtained using optimized growth conditions. Low-temperature micro-photoluminescence spectroscopy exhibits sharp excitonic emission lines from single QDs without the necessity of further processing steps. The combination of excitation power-dependent and polarization-resolved photoluminescence measurements reveal a characteristic exciton-biexciton behavior with biexciton binding energies that range from 3.5 to 4 meV and fine-structure splitting values down to 20 μeV.

The authors fabricate rolled up microtubes consisting of $\text{Si}/{\text{SiO}}_x$ on Si substrate and analyze the possibility to use them as a refractometric sensor. An aqueous sugar solution is inserted into the microtube, which leads to a change in refractive index and, as a result, to a detectable spectral shift of the whispering gallery modes. Experimental results can fit well with finite-difference time-domain simulations, which are used to determine the sensitivity of this tube refractometer. The ratio of spectral sensitivity to channel cross-sectional area of the refractometer is particularly striking and allows analysis of fluid volumes in the range of femtoliters. A comparative discussion with other existing refractometer schemes concludes this work.