A Compact Four-Wavelength Quantum-Cascade Laser Source

A four-wavelength quantum-cascade (QC) laser source that operates using a single current channel is presented. The source includes two different heterogeneous cascade QC lasers, one with emission wavelengths of 7.0 $mu{hbox {m}}$ and 11.2 $mu{hbox {m}}$, and the other with 8.7 $mu{hbox {m}}$ and 12.0 $mu{hbox {m}}$ . For 3.0-mm and 3.5-mm cavity lengths, QC lasers with emission wavelengths of 8.7, 11.2, and 12.0 $mu{hbox {m}}$ have threshold current densities within less than a factor of 2, which allows them to be conveniently driven in series by a single current source.