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In this work, we propose to employ strong optical feedback to narrow the spectral linewidth of quantum cascade lasers without using any phase control. Rate equation analysis demonstrates that optical feedback beyond a certain level always reduces the laser linewidth for any feedback phase. It is also found that the linewidth becomes less sensitive to the feedback phase for higher feedback strength. Simulations show that optical feedback with a feedback ratio of −10 dB can suppress the laser linewidth by about two orders of magnitude. This is in contrast to near-infrared laser diodes, which can be easily destabilized by strong feedback. [ABSTRACT FROM AUTHOR]

Narrow-linewidth mid-infrared laser sources are highly demanding for high-resolution gas spectroscopy applications. Interband cascade lasers (ICLs) are power-efficient laser sources emitting in the mid-infrared range. This work unveils the low phase noise characteristics of distributed feedback ICLs driven by a battery source. We show that the measured spectral linewidth of ICLs is as narrow as 284 kHz (at a 1 ms observation time), which is smaller than those of common quantum cascade lasers. On the other hand, raising the pump current reduces the intrinsic linewidth down to 12 kHz. The linewidth broadening factor is in the range of 2.0–3.0, leading to a Schawlow–Townes linewidth as narrow as 1.6 kHz. This work suggests the high potential of developing battery-driven, high-resolution gas spectroscopy instruments using ICLs. [ABSTRACT FROM AUTHOR]