Frequency combs are ideal candidates to realize miniaturized spectrometers without moving parts. ICLs are perfect for the realization of miniaturized spectrometers, due to their low power consumption and the possibility to build sensitive on-chip detectors using the same epilayer material. Here, we present an overview of our current work on ICL frequency combs. This includes the generation of self-starting frequency combs utilizing their gain nonlinearity, resulting in a dominant frequency modulation similarly to quantum cascade lasers frequency combs. Furthermore, we demonstrate the generation of 3ps pulses with a peak to average power ratio of over 40 via active mode-locking.
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.
Following the goals of single-chip integrated dual comb spectrometers, we report on recent results on mid-infrared frequency combs. We demonstrate frequency comb operation with a bi-functional quantum cascade material, which allows the integration of lasers and detectors on one chip. With this device, we hold the power and efficiency record of QCL frequency combs. In the second part, we will present first evidence of frequency comb generation using mode-locked interband cascade lasers. With the demonstration of picosecond pulse generation in the mid-infrared, we open a new path towards battery driven sensitive high-resolution spectrometers miniaturized to chip-scale dimensions.