Widely tunable pulsed erbium-doped ZBLAN fiber laser

Abstract

Pulsed fiber lasers with wideband operation in the mid-infrared (mid-IR) wavelength regime (2 ∼ 5 µm) have aroused considerable attentions for their potential applications in defense, laser microsurgery, mid-infrared spectroscopy, and nonlinear applications. Among the generation methods, high concentration Er3+-doped ZBLAN fiber lasers have become one of the most promising candidates to generate mid-IR laser around 3 µm regime for the high efficiency, broad emission spectral range, and the commercial and cost effective diode pump lasers at the 975 nm. Up to now, the ultrafast fast Er3+-doped ZBLAN fiber laser with pulse width down to 207 fs, power up to 1W have been realized. With novel two dimensional materials, the Er3+-doped ZBLAN fiber laser modulated by graphene, topological insulator and black phosphors have been demonstrated. However, the broadband operation potential needs to be further explored. In addition, the nanomaterials suffer from the oxidation and humidity for practical applications, so the preparation and transfer method should be improved. Here, we adopted the two-dimensional topological insulator as saturable absorber. To improve the stability of the saturable absorber, polymethyl methacrylate (PMMA), an insulating polymer, has been used to sandwich the topological insulator film. With the improvement, the optimized saturable absorber can act as an attractively alternative method for high power pulsed Er3+-doped fluoride fiber laser. We have also used Volume Bragg gratings (VBGs) recorded in photo-thermo-refractive glass to narrow the spectral width. Compared with other methods, VBGs have the advantages of high diffraction efficiency, narrow spectral width, a high damage threshold, and good thermal stability. These properties make them very attractive as appropriate spectral narrowing and wavelength selection components in high-power, narrow-linewidth, and tunable laser sources. With the topological insulator saturable absorber, we have demonstrated Q-switched Er3+-doped fluoride fiber laser spectrally narrowed by VBGs. Stable pulse trains with pulse duration down to about 900 ns, repetition rate of 50 kHz have been achieved. Meanwhile, the wavelength tuning range can cover 2762nm to 2824 nm. The spectral width over the whole tuning range is less than 0.3 nm. The method may provide an inroad for developing high performance mid-IR fiber lasers.