Abstract

Ultrashort pulse (USP) fiber lasers are of great interest for their wide applications in telecommunication, frequency metrology field, dual comb spectroscopy, THz pulse spectroscopy and etc [1]. Hybrid mode-locking (ML) for USP generation have attracted a great attention due to their capabilities of enhancing pulse quality and providing reliable ML startup by taking advantage of a co-action of two saturable absorbers (SA) ̶ a slow SA such as SESAM, single wall carbon nanotubes (SWCNTs-SA) or graphene, and a fast absorber based on nonlinear polarization evolution (NPE) effect [2]. It should be noted that compared to quantum well-based SESAMs, SWCNT-SAs benefit from much more easier and cost-effective fabrication techniques, possibility of being used in both linear and ring cavities, ultrafast carrier relaxation time and significantly enhanced noise characteristics. However, despite well-elaborated SWCNT-based film fabrication technologies, it is difficult to control such a crucial characteristic for laser mode-locking as an absorber response time during SWCNT-SA fabrication process. Moreover, a polarization dependence of saturable absorption can not be controlled since SWCNTs orientations are randomly distributed. All these features make SWCNT-SA characteristics as well as corresponding mode-locked laser performance absolutely unpredictable [3]. Recently it have been shown by X. Xu that well-aligned SWCNT-SA could be one of the ways to solve these drawbacks in ML of fiber lasers [4]. However, the proposed synthesis method is quite complicated for serial production of well-aligned SWCNT-SAs with the required parameters.

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