Passively mode locked all-fiber ytterbium oscillator with integrated hollowcore photonic bandgap fiber

Abstract

Passively modelocked Yb based fiber oscillators were intensively investigated in the last decade, as they offer compact design and environmental stability. One of the main directions of research was to utilize fiber-integrated dispersion compensating elements in the cavity to ensure self-consistent solutions of the mode-locking mechanism, since conventional single-mode fibers (SMF) have normal dispersion below 1.3 µm. The application of hollow-core photonic bandgap fibers (HCF) for dispersion control is advantageous because in addition to their possibly anomalous group velocity dispersion (GVD) in the Yb wavelength range they have reduced nonlinearity compared to solid-core fibers. There have been experimental demonstrations of such lasers in the weakly stretched soliton [1] and in the similariton regimes [2]. These setups included free-space optics for coupling light into and out of the HCF and also for the alignment of the appropriate polarization states. However, for alignment-free operation and high stability an all-fiber setup is desired. Here we report a self-starting passively mode-locked fiber laser containing a HCF spliced into the cavity to provide anomalous GVD. The laser operates in the stretched-pulse regime, close to the zero cavity dispersion. To the best of our knowledge this is the first implementation of integrated HCF based intracavity dispersion control.