Quantum cascade lasers with a heterogeneous cascade: Two-wavelength operation

A quantum cascade (QC) laser with a heterogeneous cascade containing two su bstacks previously optimized to emit at 5.2 mum and 8.0 mum wavelengths, re spectively, is presented. The low-temperature performance of the two-wavele ngth laser is comparable to the respective homogeneous stack lasers, indica ting no penalty from the heterogeneity of the cascade. Each substack is app ortioned the optimum fraction of the applied bias. This demonstrates the ge neral applicability of this scheme. In addition, an etch-stop layer inserte d between the two substacks allowed fabrication of a "tap" into the cascade . The latter was used to selectively manipulate the laser threshold of one substack, turning the 8.0 mum laser on and off while the adjacent 5.2 mum Q C laser was operating undisturbed. (C) 2001 American Institute of Physics.