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A comparative study of the gain spectra of quantum-dot lasers at high carrier densities is reported. The gain spectra of quantum dot lasers under a constant junction temperature (obtained by the use of Fabry-Perot modes as a temperature gauge) and under constant heat-sink temperatures are measured. Negative differential gain, observed for the ensemble of quantum dot ground-states is shown to be mainly due to free carrier effects, where increasing dephasing effects, combined with saturated gain, result in spectral broadening and a reduction in the peak gain.

This paper reports on the direct comparison of Hakki-Paoli and segmented contact method gain spectra measurement techniques for InAs/GaAs 1.3m quantum dot laser material. This was made possible by realizing a single-mode segmented contact device structure. The differences in required apparatus, ease of measurements, signal to noise ratio, and relative advantages and disadvantages of these two complementary techniques are discussed under continuous wave operation. As expected, at current densities (prior to possible self heating effects) the techniques are shown to give essentially identical results. However, the segmented contact method is demonstrated to be more accurate for internal loss measurements. A method to remove self heating effects in the Hakki-Paoli measurements is described and allows the gain and spontaneous emission measurements to be performed at carrier densities as high as 5.5kA/cm2with a constant cavity temperature.

In this work the use of two identical QD SOAs to enhance the performance of swept laser system for OCT applications is discussed, resulting in an increase in bandwidth up to 94nm. The combination of GaAs based QD SOAs and InP based QW SOAs for realizing broad bandwidth sources for OCT system is described. For the swept laser source a 154nm spectral bandwidth from 1193nm to 1347nm and an average power of 8mW is obtained and for the filtered ASE source a 225 nm bandwidth is demonstrated.