Dispersion step tuning fiber laser based on a Mach–Zehnder interferometer

This paper presents a wavelength-stepped swept laser based on a dispersion-tuned swept laser with the integration of a Mach–Zehnder interferometer, enabling a transition from continuous wavelength sweeping to wavelength-stepped sweeping. A comprehensive investigation of this laser is conducted, wherein different modulation schemes are employed to dynamically compare the switching mode, static-sweeping mode, and sweeping mode; the absence of mode hopping in the sweeping mode of the laser is verified. However, it is observed during experiments that the wavelength always remains stationary for a long time during the initiation of sweeping and change in sweeping direction, exhibiting latency compared to the modulation frequency variations. Through a simplistic modeling analysis of the composite cavity, it is revealed that the detuned state of the sub-cavity plays a critical role in the stable operation of the laser. Subsequently, simulation verification using the Ginzburg–Landau equation supports this observation. Additionally, compared to dispersion-tuned swept lasers, not only the linewidth significantly is narrowed in the proposed laser, but it also demonstrates enhanced stability during the sweeping process. This study provides, to our knowledge, a new laser source for ultra-fast optical imaging, ranging, and sensing applications, and presents novel methods and theoretical models for linewidth compression in swept lasers.