All-fiber passively mode-locked laser based on an electron beam evaporation grown Co²⁺:ZnSe film saturable absorber

Abstract

We experimentally demonstrated an all-fiber mode-locked erbium-doped laser based on Co2+:ZnSe (Cobalt, Zinc Selenide) thin film as the saturable absorber (SA), which was grown on the fiber taper by electron beam (e-beam) evaporation technology. The modulation depth, non-saturable loss and saturation intensity were found to be ∼12%, 76% and 1.89 MW/cm2, respectively. The X ray diffraction (XRD) results showed that the Co2+:ZnSe thin film was provided with the cubic zinc blende structure. The scanning electron microscope (SEM) and atomic force microscopy (AFM) images showed the prepared thin film has a smooth and uniform surface. When the fiber-taper Co2+:ZnSe SA was inserted into an erbium-doped fiber laser cavity, a stable mode-locked pulse was obtained. The mode-locked pulses had a pulse repetition rate of 17.83 MHz and pulse duration of ∼4 ns throughout the mode-locked operation range of 200-600 mW. The recorded maximum average output power was ∼4.88 mW. The signal to noise ratio (SNR) was obtained to be 64.9 dB, which indicates the favorable stability of the mode-locked pulse. These results demonstrate the Co2+:ZnSe thin film grown on a fiber taper has high optical quality and implementation of stable pulse operation on passively mode-locked Er-doped fiber lasers.