Research On A New Broadband Saturable Absorber All-fiber Mode-locked Laser

With the rapid development of science and technology,people's ability to understand various natural and non-natural phenomena in the material world is becoming stronger and stronger,and the requirements for the tools they need are constantly improving.Especially,the research demand for many ultrafast phenomena has greatly promoted the development of ultrashort laser pulses.The advantages of ultra-short laser,such as narrow pulse width and peak power,make it have important application value in the fields of industrial production,laser communication science,extreme detection,medical devices and microsurgery.Lasers based on different working substances have been fully developed and applied in the decades since the laser was first born.In recent years,fiber laser has further accelerated the practical process of laser industry due to its advantages such as exccllent beam quality,strong anti-interference ability,simple thermal management,high degree of intensification,high conversion efficiency and low operation costThe most common method to realize short pulse is mode-locking technique.Among them,the realization method based on saturable absorber has attracted many researchers' interest because of its simplicity and convenience.The early saturable absorbers(dyes and semiconductor saturable absorption mirror)made the development of pulsed lasers slow due to the limitations of technology and material properties.With the rapid development of nanomaterials,various new low-dimensional materials have become an important focus in the field of ultra-short pulse fiber lasers.Based on this research background,a series of studies have been carried out on a new broadband saturable absorber all-fiber laser.Among them,the preparation method and technology of saturable absorber have been improved in order to improve the performance of the fiber laser.The content of this paper is as follows:1.A carboxyl graphene oxide(GO-COOH)with similar optical properties but better water solubility as graphene oxide was proposed as a saturable absorber.The evanescent field saturable absorber device was fabricated by combining carboxyl graphene oxide aqueous solution with side polished fibers.A stable mode-locked erbium-doped fiber laser with a pulse width of 500 fs and a signal-to-noise ratio of 80 dB was obtained by inserting the S A device into the ring laser cavity.The experimental results show tliat carboxyl graphene oxide has excellent saturable absorption properties.The application of D-type fiber not only ensures the all-fiber structure of the laser,but also further improves the damage threshold of mode-locked devices by using the interaction between evanescent field and absorber material.2.A few-layer MoS2 saturable absorber based on fluoromica(FM)was fabricated by Langmuir-Blodgett(LB)technology.FM sheets with thickness of 20 ?m have high damage threshold and good heat dissipation ability.The films prepared by LB technology are more uniform and dense than those prepared by traditional spin-coating method,which makes the unsaturated loss of saturable absorber devices smaller and can effectively reduce the intracavity loss of lasers.In addition,compared with magnetron sputtering and chemical vapor deposition,the absorber prepared by LB undergoes a continuous phase transition from gas phase to liquid phase and then to solid phase at room temperature and pressure without damage.MoS2/FM SA devices are applied to fiber lasers.Soliton mode-locked and tightly bound soliton mode-locked pulses are obtained under different polarization states.The experimental results show that LB method provides a low-cost and effective method for fabricating saturable absorber devices with compact surface and uniform material distribution.3.A new-type of MoS2/SiO2 SA was prepared by sol-gel method.The precursor sol was obtained by hydrolysis and condensation reaction with tetraethoxysilane(TEOS),ethanol,water and hydrochloric acid as the reactant,and then MoS2 was added to obtain MoS2 sol-gel glass.The SA device is based on inorganic substances,which greatly improves the optical damage threshold of the absorber while protecting the material from air oxidation.It was applied to ytterbium-doped fiber(YDF)laser,and the stable mode-locked pulse was successfully obtained under normal dispersion state with a pulse width of 13.8 ps and an average output power of 34.6 mW.The fluctuation of central wavelength and spectral bandwidth in 7-days is as low as 0.9%.Our work shows that the application of sol-gel glass SA in fiber laser not only improves the performance parameters of the laser,but also provides a new approach to improve the optical damage threshold of the photonic device.