Investigation On Pulsed Fiber Laser Based On New Two-dimensional Materials

In the past few decades,nonlinear optics has been one of the fastest-growing scientific fields,which can cause many interesting optical phenomena,such as second harmonic generation,Kerr effect,and saturated absorption.It is generally believed that the discovery of nonlinear optical materials will play a vital role in basic scientific research and industry.In a material with saturated absorption,the absorption of light will increase the light intensity.After the early use of dyes as saturable absorbers to generate high peak power and ultra-short laser pulses through passive Q-switching or mode-locking,semiconductor saturable absorber mirrors have been developed and become the mainstream materials in this field.Femtosecond laser is one of the most valuable products facilitated by saturable absorbers,which can be used for high-precision micro-nano processing,molecular spectroscopy and information processing.Renently,researchers have begun to pay attention to nano two-dimensional materials for the development of novel saturable absorbers,including carbon nanotubes,graphene,black phosphorus,transition metal dichalcogenides,topological insulators and metal carbonitrides,which have witnessed their applications in this field.The main work of this paper is to explore the saturation absorption characteristics of the new ternary two-dimensional materials and the performances of Q-switching and mode-locked lasers.1.The self-made Mo0.5W0.5S2/Polyvinyl alcohol film is prepared into a saturable absorption device.The modulation depth of Mo0.5W0.5S2/Polyvinyl alcohol film is 12% measured by a twin detector technique,and the saturated absorption intensity is 4.5 MW/cm2.Stable Q-switching is achieved in an erbium-doped all-fiber laser.The shortest pulse width is 1.29 ?s,the maximum single pulse energy is 13.97 n J,and the repetition frequency ranges from 49.9 k Hz to 85.94 k Hz.2.In order to achieve 1.5?m mode locking and suppress the envelope of the Q-switched pulse,this experiment has adopted two improvement measures.The first is the improvement of the saturable absorbers/Polyvinyl alcohol film transfer technology;the second is the use of the balance of fiber nonlinear effects and negative dispersion.For the first time,we have experimentally demonstrated a mode-locked Er-doped fiber laser based on Mo0.5W0.5S2 SA.The center wavelength is 1558.4 nm with the spectral width of 6.33 nm.The mode-locked pulse width is 575 fs.The repetition frequency is 4.873 MHz.The signal-to-noise ratio is as high as 53 d B.The peak power is 268 W,and the corresponding maximum single pulse energy of 0.154 n J.3.Research on the all-fiber passively Q-switched erbium-doped fiber laser based on MXene saturable absorbers and MXene/Mo S2 saturable absorbers.The MXene saturable absorbers and Mxene/Mo S2 saturable absorbers were transferred to the end face of the optical fiber by the liquid deposition method,and their nonlinear absorption characteristics were measured.The modulation depth of Mxene saturable absorbers is 3.54%,and the saturable absorption intensity is 0.47 MW/cm2;the modulation depth of Mxene/Mo S2 saturable absorber is 2.1%,and the saturable absorption intensity is 7.22 MW/cm2.The shortest pulse width of Q-switching pulse based on MXene saturable absorbers is 2.1 ?s,the maximum single pulse energy is 10.5 n J,and the repetition frequency range is from 48.58 k Hz to 76.57 k Hz;the shortest pulse width of Q-switching based on MXene/Mo S2 saturable absorbers is 1.2 ?s,the maximum single pulse energy is 42.6 n J,and the repetition frequency range is from 65.96 k Hz to 98.52 k Hz.