Abstract

During the last couple of years, quantum cascade (QC) lasers have reached a high degree of maturity. Yet, there are still several interesting spectroscopic applications which require higher average output powers than currently available. Consequently, we present here single-mode QC lasers in different configurations and with greatly improved average powers. The active region of the first investigated device consists of three coupled quantum wells with a diagonal electronic transition at 121 meV. Without epitaxial overgrowth on the 1^st order grating and using a lateral contact scheme [1], we fabricated 1.5 mm long and 55 μm wide DFB lasers from this material; the resulting L-I-V-curves are shown in figure 1. The threshold current at room temperature was 5.5 A, corresponding to a threshold current density of 6.6 kA/cm²; at 1.5 % duty cycle and 300 K, the peak output power was on the order of 230 mW. The maximum average power output was achieved with a duty of 3 %. At −30 °C, an average power of 14 mW was seen, while at 60 °C, the power dropped to 1.5 mW. From the dependence of the threshold current we found a T₀ value of 300 K; this is possible because of an improved match between Bragg and gain peak at elevated temperatures. The inset of figure 1 shows the emission spectra of this laser at different temperatures. The wavelength changes linearly at a rate of Δk/ΔT=−0.078 cm⁻¹/K. We explain this augmented temperature tuning rate by strong heating effects of the device at high duty cycle.

© 2000 IEEE