Repulsive intermode beat synchronization in interband cascade laser frequency combs (Conference Presentation)

Optical frequency combs are coherent sources that emit a series of evenly spaced lines. In the mid-infrared, comb based spectroscopy is of particular interest and, without the need of any movable parts, will potentially lead to a breakthrough in miniaturization. Interband cascade lasers, with their low power consumption and inherent detection functionality, are an ideal candidate for practical implementations. Here, we present the generation of low-dissipation optical frequency comb utilizing interband cascade lasers. Other than one might have expected, the long lifetime of the interband transition does not automatically lead to slow gain dynamics that would favor in-phase mode-locking. We discuss why ICLs should be considered as fast gain media and why passive mode-locking is difficult or even impossible to be achieved. We applying shifted-wave interference Fourier transform spectroscopy to show that ICL frequency combs naturally favor repulsive intermode beat synchronization with the same chirped FM character recently found in QCL combs. Furthermore, we show first evidence of multiple normal modes of the intermodal beats in frequency combs and picosecond pulse generation from ICLs.