The tunability of ASE laser with transverse feedback was studied theoretically and experimentally. We found theoretically that a miniature OFFIRL with transverse feedback would give FIR laser with very broad frequency characteristics as shown in Fig.l.
Yikun Lin, Yikun Lin,
"Miniature OPFIRL with broad frequency tunability", Proc. SPIE 1576, 16th International Conference on Infrared and Millimeter Waves, 15762L (1 October 1991); doi: 10.1117/12.2297806; https://doi.org/10.1117/12.2297806