High brightness tree-array quantum cascade lasers (QCLs)

We demonstrate phase-locked, high power, tree-array quantum cascade lasers based on ridge waveguides with near diffraction-limited beam quality from the single-emitter side at a wavelength of 8.6μm. Tree-arrays based on ridge waveguides are promising for power scaling of QCLs, and are simpler to fabricate than buried heterostructure waveguides. Understanding the fabrication sensitivity of ridge waveguide tree-array QCLs is important for assessing their viability for mass fabrication. An analysis of fabrication tolerance and guidelines for the design of efficient MMI couplers is presented.