The low-intensity luminescence of ${\mathrm{ZnSe}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Te}}_{\mathrm{x}}$ with x=1% exhibits several unusual features which are attributed to the occurrence of efficient exciton self-trapping induced by Te atoms. This type of exciton localization is strikingly different from that observed in other II-VI or III-V mixed crystals.

Evidence for biexciton formation in ZnSe quantum wells is reported. The molecular binding energy is found to increase by one order of magnitude over the bulk value in narrow wells, in agreement with a recent calculation by Kleinman.

Photoluminescence (PL) from InAs self-assembled quantum dots (QD) embedded in the AlAs matrix was strong and clean around 700 nm. PL efficiency remained quite high at room temperature compared to other QD systems embedded in GaAs cladding layers. Transmission electron microscope pictures from the structure showed a clear formation of relatively small and coherently strained InAs QD. The observed blueshift with accompanying broadening of PL spectra with the increase of excitation power is interpreted in terms of local carrier tunneling in a dense QD system. The PL peak redshift with the increase of temperature was very large, as much as 228 meV. The anomalous shift is interpreted as due to activation-energy differences between dots of different sizes.

Five stacks of InAs quantum dots (QDs) with InGaAsP barriers were grown on (100) InP and luminescence characteristics were analyzed. Cross-sectional transmission electron microscopy shows that small dots with a lateral size of ∼30 nm and a height of ∼3 nm are formed with an areal density of ${\text{∼5×10}}^{10}$ ${\mathrm{cm}}^{\text{−2}}.$ The QDs emit strong photoluminescence (PL) peaks in the range of 1.4–1.6 μm that can be controlled by nominal InAs thickness. The integrated PL intensity from QDs stays very high at room temperature as much as 20% of that at 10 K. At weak excitation, the carrier lifetimes are measured to be almost the same across the whole PL band at low temperature with a value of ∼4 ns and they remain at that value at room temperature. These characteristics strongly evidence that individual QDs are well isolated and have a strong carrier confinement at room temperature.

Low noise figures of 3.3–3.9 dB have been acheived in flat gain L-band EDFAs over 30 nm with < 1 dB gain variation. A dual-stage configuration with optimised use of backward amplified spontaneous emission is employed for low noise and high efficiency operation with only 980 nm pumping.