Spectra Characterization of Ring Quantum Cascade lasers

The quantum cascade laser (QCL) based ring structures are becoming hot research areas for laser beam control [1] and mode-locking applications [2] . Recently, with the strong nonlinearity of active region, mid-infrared frequency comb based on ring QCLs have been demonstrated [3] , [4] , showing great potential of pulse generation without using active mode-locking scheme. In this work, we report the development of mid-infrared frequency comb based on the ring QCL with optimized structure. Besides the unique lasing mode dynamics of the ring QCLs, the device shows a spectrum regime which can be reasonably fitted by a sech 2 function.