| Visible pulse lasers play an important role in remote sensing,medicine,and communications.Compared to second-harmonic visible lasers,rare-earth-doped visible fiber lasers offer compact construction,are maintenance-free,and have high efficiency.Pr3+ is the only rare earth ion that emit multi-wavelength in visible range at room temperature.Furthermore,ZBLAN(ZrF4-BaF2-LaF3-AIF3-NaF)fiber possesses low phonon energy(580 cm-1)and low transmission loss(<0.1 dB/m)in visible regions.Hence,Pr3+-doped ZBLAN fiber has been considered as excellent gain medium for visible fiber lasers.Passively Q-switching is more likely to be combined with fiber lasers than actively one as it without introducing non-optical device.Recently,two-dimensional materials have attracted great attention in the area of passively Q-switching fiber laser.Like graphene,topological insulator(Bi2Se3)possesses large modulation depth,ultrabroad wavelength saturable absorlption range and low cost,and has been widely used as saturable absorber(SA)in the research of ultra-short pulse including Q-switching and mode-locking.In the past few years,several research works proposed that Bi2Se3 was suit for pulsed fiber laser operation and showed a broadband saturable absorption.Base on the investigation above,we numerically simulate the dynamic evolution process of Q-switched pulses in the laser cavity,and experimentally demonstrated a compact Bi2Se3-based orange passively Q-switched all-fiber laser at 604 nm.The main contents and innovations are as follows:1.Numerical simulation of Bi2Se3-based orange passively Q-switched fiber laser was developed.Principle of Q-switching and rate equation is the base of simulation,and Runge-Kutta method is used to unfold the equation.The density of photon number in the cavity,inverted population density of gain mediun and ground state particles of SA have a ratio relationship of 1:1:1.Q-switched pulse frequency is proportional to the pump rate,while inversely proportional to the modulation depth of SA.The pulse duration decreases with the increase of the modulation depth of SA.Theoretical analysis could support the experimental research.2.Achieving the all-fiber structure with the help of two dielectric mirrors which were prepared after fiber end face was solved using manual fiber polishing technique.The compact laser resonant cavity consists of two dielectric films.One was an input mirror with a high-transmittance of 78.22%at the pump wavelength of 444 nm and a high reflectivity of 97.35%at the laser wavelength of 604 nm.The other was an output mirror with a transmittance of 7.2%at 604 nm.3.A simple passively Q-switched praseodymium-doped all-fiber laser at visible wavelength of 604 nm was experimentally demonstrated.The repetition rate of the achieved 604 nm Q-switching pulse can be widely tuned from 86.6 to 187.4 kHz,the pulse duration can be as narrow as 494 ns,and a signal noise rate of～40 dB.To the best of our knowledge,this is the shortest operation wavelength of a Bi28e3-based pulsed all-fiber laser at 604 nm. |
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