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A hollow waveguide integrated optic QCL beam combiner

We describe a beam combiner based on a cascade of dichroic components implemented in a hollow waveguide integrated optic format. The approach results in a compact, rugged, optically robust solution for providing simultaneous multi-wavelength emission in the near and mid-IR atmospheric transmission windows. In the approach the individual dichroic beam combiner components are held in precision alignment slots in the hollow waveguide circuit and the different input wavelengths are guided between the components to a common output port. The hollow waveguide circuit and the alignment slots for the components are formed in the surface of a Macor (machinable glass-ceramic) substrate using precision CNC machining techniques. The hollow waveguides have fundamentally different propagation characteristics to solid core waveguides leading to transmission characteristics close to those of the atmosphere while still providing useful light guidance properties. Because of the hollow nature of the core, the transmission efficiency and power handling of the hollow waveguide circuit can be designed to be very high across a broad waveband range. The specifications for the dichroic beam combiners and the design of the hollow waveguide circuit are described in relation to a beam combiner for combining three QCLs emitting at 3.95 μm, 4.05 μm and 4.6 μm and a Ho:YAG laser emitting at 2.1 μm. Details of the design, modeling and manufacturing work, and preliminary assessments of the associated components, are described.