Quantum cascade laser with high efficiency operation and related systems and methods

A quantum cascade laser (QCL) comprising:

• a substrate;
• and
• a sequence of semiconductor epitaxial layers adjacent said substrate and defining an active region, an injector region adjacent said active region, and a waveguide optically coupled to said active region;
• said active region comprising a plurality of stages, each stage having an upper laser level and a lower laser level defining respective first and second wavefunctions, said waveguide and said active region defining a two-level ridge configuration, a first level ridge extending into said active region, a second level ridge extending to a depth less than that of the first level ridge.

A quantum cascade laser (QCL) comprising:

• a substrate;
• and
• a sequence of semiconductor epitaxial layers adjacent said substrate and defining an active region, an injector region adjacent said active region, and a waveguide optically coupled to said active region;
• said active region comprising a plurality of stages, each stage having an upper laser level and a lower laser level defining respective first and second wavefunctions, said waveguide and said active region defining a multi-channel configuration with greater than 2 channels.

A quantum cascade laser (QCL) system comprising:

• a QCL comprising
• a substrate, and
• a sequence of semiconductor epitaxial layers adjacent said substrate and defining an active region, an injector region adjacent said active region, and a waveguide optically coupled to said active region,
• said waveguide defining first and second opposing facets configured to respectively emit first and second laser outputs,
• said active region comprising a plurality of stages, each stage having an upper laser level and a lower laser level defining respective first and second wavefunctions,
• the upper laser level having an upper laser level average coordinate and the lower laser level having a lower laser level average coordinate, the upper laser level average coordinate and the lower laser level average coordinate having spacing therebetween of less than 10 nm,
• wherein wave functions for all active region energy levels located below the lower laser level have greater than 10% overlap with said injector region,
• wherein energy spacing between uppermost laser levels exceeds 60 meV, and
• wherein a depth of said active region is greater than 100 meV;
• and
• a plurality of mirrors, and a half-wave plate configured to combine the first and second laser outputs.

A method of making a quantum cascade laser (QCL), the method comprising:

• forming a sequence of semiconductor epitaxial layers adjacent a substrate and defining an active region, an injector region adjacent the active region, and a waveguide optically coupled to the active region;
• the active region comprising a plurality of stages, each stage having an upper laser level and a lower laser level defining respective first and second wavefunctions;
• the upper laser level having an upper laser level average coordinate and the lower laser level having a lower laser level average coordinate, the upper laser level average coordinate and the lower laser level average coordinate having spacing therebetween of less than 10 nm;
• wherein wave functions for all active region energy levels located below the lower laser level have greater than 10% overlap with the injector region;
• wherein energy spacing between uppermost laser levels exceeds 60 meV;
• and
• wherein a depth of the active region is greater than 100 meV.