Abstract

Here, we propose a self Q-switched single-frequency (SF) all-fiber laser. The intra-cavity Er:Yb co-doped fiber serves not only as an active fiber for lasing but also as a fiber-type saturable absorber (SA). The self-Q-switching behavior is induced by the ground-state reabsorption of the unpumped portion of the active fiber. To achieve SF operation, double fiber loops constructed by two 3 dB optical couplers (OCs) form a cascade sub-cavity, which serves as a mode selector with a narrow bandwidth. Taking the advantage of a high damage threshold of the fiber-type SA, microjoule-level self-Q-switched SF pulses are obtained with a narrow linewidth of ${\sim}{252}\;{\rm kHz}$. Combed with the measured pulse width of ${\sim}{1.766}\;{\unicode{x00B5} \rm s}$, the corresponding time-bandwidth product is ${\sim}{0.445}$, which is very close to the Gaussian transform limit. The maximum output power of the pulsed SF laser can reach ${\sim}{100}\;{\rm mW}$. By stretching the fiber Bragg grating (FBG), the wavelength of the pulsed SF laser can be tuned.

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