Research On The Preparation Of High-performance Saturable Absorber Devices And Their Application In All-fiber Pulsed Laser

As an important branch of modern optics,nonlinear optics mainly studies the optical nonlinear phenomenon and its application.Nonlinear optics is one of great significance in the development of laser technology,spectroscopy and material structure analysis.Since the emergence of laser characterized by a high degree monochromaticity,high brightness and high directionality,which has also made nonlinear optics been one of the fastest growing scientific fields in recent decades.Nonlinear optical processing is closely related to the development of ultrashort pulse laser technology.Among them,the saturable absorption plays a key role as a nonlinear optical phenomenon to obtaining ultrashort pulses.One of the effective technologies to realize ultrashort pulse is mode-locked based on saturable absorber（SA）.The SA rely on the nonlinear optical response of a saturable absorbing material.The optical absorption of the SA decrease with the increase of the incident light intensity.The ultrashort laser pulses with high peak power can be generated by mode-locked or Q-switched,depending on the nonlinear optical response of the SA.SAs-based fiber lasers has the advantages of compact structure,good mechanical stability,high reliability,good beam quality,high scalability,easy implementation,and low cost.In recent years,fiber lasers have been widely used in industrial laser micromachining,ultrafast information processing,and molecular spectroscopy.However,the commercial semiconductor saturable absorption mirror（SESAM）still has some defects,such as limited working bandwidth,expensive fabrication cost and complex process.Therefore,people have been concerned about the saturated absorption characteristics of low dimensional nanomaterials,in order to develop a broadband SA with high performance for ultrashort pulse.At present,it has proves that these materials have good saturated absorption properties and application prospects.However,broadband SA have not been successfully used in industrial ultrafast lasers.Hence,the development of excellent nonlinear optical properties of new materials still has far-reaching significance.Furthermore,different preparation methods of SA film lead to different performance,which have a significant impact on the laser output characteristics.Hence,the suitable preparation methods of SA device is prerequisite for practical research.To sum up,it is highly desirable to develop a new type of practical SA device with a high power tolerance,long-term reliability,and low cost,which are suitable for practical applications.In order to study high-performance SA devices and improve the performance of the laser,the content of this thesis is arranged as follows:1.The optical properties and application of WS₂/Si O₂SA fabricated by the sol-gel method.Compared with optical fibers,silica prepared by sol-gel method has similar mechanical strength,refractive index,optical absorption and transmission properties.The SA device fabricated by sol-gel technology combined with WS₂material can effectively improve the optical damage threshold of SA devices.What is more noteworthy is that the SA material is wrapped inside Si O₂,which isolates the influence of the external environment and has a high promotion effect on the long-term stability of the laser.The SA device was obtained by wrapping WS₂material with Si O₂for the first time.Stable soliton pulse operation with pulse width of 58 ps,average output power of 56.8 m W and repetition rate of 19.03 MHz was realized in ytterbium-doped fiber laser.In addition,when it is applied to erbium-doped fiber laser,a stable mode-locked pulse laser is also realized.The pulse width is 325 fs and the output power is 39.6 m W.2.A novel boron nitride（BN）SA thin films with uniform distribution and controllable thickness were prepared by magnetron sputtering deposition（MSD）.This film is deposited on fluoromica（FM）substrate with good optical properties.FM has good heat dissipation capacity and low insertion loss,and can withstand high laser power without damage.BN material is a wide gap semiconductor similar to Si C.It has ideal mechanical strength,good chemical stability,thermal stability,high thermal conductivity and excellent insulation.In addition,BN also has excellent saturation absorption capacity.Here,both the base material and the boron nitride saturable absorber material have good physical and chemical properties.The combination of the two was successfully fabricated into a BN-FM SA device.When applied in erbium-doped fiber laser,the passive mode-locked pulse operation with pulse duration of 237 fs and average output power of 35.39 m W is realized.3.ZrC film was deposited by MSD technology onto the D-shaped fiber（DF）as well as demonstrated the nonlinear optical properties of Zr C film.The saturation intensity and the modulation depth of Zr C film were measured to be 197.6 MW/cm²and11.9%,respectively.After inserting the Zr C SA into the erbium-doped fiber laser cavity,a passive mode-locked pulses were formed.In mode-locked operation,conventional solitons with an ultrashort pulse duration of 395 fs,and the output power with 49.86m W are achieved in the communication band.4.A novel type of DF buried Mo₂C saturable absorber was successfully prepared by combining MSD technology with sol-gel method.First,MSD technology was used to deposit Mo₂C material with uniform thickness on the surface of DF,and then the Mo₂C material was buried between DF and Si O₂prepared by sol-gel technology.The SA device is applied to erbium-doped fiber laser to realize high-energy stable Q-switched pulse operation with maximum pulse energy of 430.47 n J.After that,a high-power mode-locked pulse with pulse width of 199 fs and output power of 54.13m W was successfully obtained by adjusting the pump power and polarization state in the cavity.Further,the bound state soliton pulse output based on MXene SA is obtained for the first time,which has a pulse width of 312 fs and a soliton interval of 1.26 ps.Moreover,by inserting buried Mo₂C SA into ytterbium-doped fiber laser,the stable dissipative soliton mode-locked pulse are obtained with pulse width of 23 ps.5.A novel Mo₂C/FM SA device was fabricated and used to realize mode-locked pulse output.The uniform and compact Mo₂C films were deposited on the FM by MSD method.In order to increase the laser damage threshold,an additional protective layer of silicon oxide was deposited on the Mo₂C.In this work,Mo₂C/FM SA inserted into erbium-doped fiber laser to achieve mode-locked operation.This pulse duration and average output power of the laser pulses are 313 fs and 64.74 m W.In addition,a12^th-order sub-picosecond harmonic mode-locked is generated.The maximum repetition rate is 321.6 MHz and the shortest pulse duration is 338 fs.6.By encapsulating the self-made SESAM as a device,a linear laser cavity with all fiber structure is built to realize mode-locked operation.And then,a picosecond fiber laser is assembled.Self-starting mode-locked is observed at the pump power of 80 m W.The center wavelength of the obtained pulsed laser is 1028.61 nm,the corresponding3d B bandwidth is 1.25 nm.The pulse width of the generated mode-locked pulse is 14.6ps.Experiments show that the self-made SESAM device can realize stable picosecond mode-locked pulse,and the structure is relatively simple and compact,which is easy to realize self-starting mode-locked operation.