Study Of Pulsed Fiber Lasers Based On Black Phosphorus Saturable Absorbers

Pulsed fiber lasers have attracted widespread interests for their advantages of compactness,stability,high efficiency and low cost.The study of saturable absorber(SA)is of great significance,for the SA plays a key role in the generation of laser pulses.Traditional SA materials are unable to meet the ever-growing demand due to their inherent shortcomings.Black phosphorus(BP),as a new type of two-dimentional(2D)material,was recently found to have unique physical properties which include the optical saturable absorbtion.And BP was found to especially applicable to infrared wavelength.Therefore,Systematic research and implementation of pulsed fiber lasers based on BP-SA is an important subject.The main achievements of this paper are the following research results:1.Working principles of SA and optically driven method are studied.The mathematical model of a SA is analyzed.The optically driven process for fiber based BP-SA fabrication is studied.2.Ytterbium-doped mode-locked fiber laser based on SAs made of few-layer BP is studied.The few-layer BP was prepared with the liquid phase exfoliation method and was deposited onto fiber facets by an optically driven process.By incorporating the BP-SA into an ytterbium-doped fiber laser cavity,stable mode-locking laser operation was achieved with a repetition rate of 46.3 MHz.The laser spectrum was centered at 1030.6 nm.Maximum output power of 32.5 m W was achieved.Our work presented a complete experimental method of Yb-doped mode-locked fiber laser using BP as SA including fabrication of SA and construction of laser.The application of BP in 1 ?m band fiber laser is preliminarily confirmed.Compared with the traditional SAs,the experimental method here greatly reduces the complexity of laser fabrication.3.Passively Q-switched wavelength-tunable 1-?m fiber lasers utilizing tapered fiber based BP-SA were demonstrated.The few-layer BP was deposited onto the tapered fibers by an optically driven process.The wavelength tunability was achieved with a fiber Sagnac loop comprised of a piece of polarization maintaining fiber and a polarization controller.Stable Q-switching laser operations were observed at wavelengths ranging from 1040.5 to1044.6 nm at a threshold pump power of 220 mW.Maximal pulse energy of 141.27 nJ at a repetition rate of 63 kHz was recorded.4.Systematic experimental demonstrations of Q-switched all-fiber lasers generating cylindrical vector beam(CVB)outputs with 2D-material-based SAs,including graphene and BP were presented.Both radially and azimuthally polarized CVB laser pulses are realized by adjusting a pair of polarization controllers combined with an offset splice spot and a fewmode fiber Bragg grating.Our experimental effort provides a concise,reliable,and complete all-fiber laser route towards pulsed CVB emissions based on 2D-material saturable absorbers.Besides,wavelength-tunable cylindrical vector beams of very narrow spectral linewidth at?1 ?m with an authentic all-fiber structure was demonstrated.Two fiber Mach-Zehnder interferometers were cascaded to achieve a 20-dB linewidth of 14.7 kHz.The central wavelength was at 1053.4 nm with a tuning range of 1.1 nm under thermal control.