| Nowadays,fiber laser is developing rapidly,and its applications are widely used in the fields of material processing,medical treatment,precision measurement and optical communication.The flexibility,reliability and compactness of this light source make it better than solid-state lasers in many aspects.The pulse operation of fiber laser is particularly important,it can significantly improve the instantaneous power,suitable for driving nonlinear optical processes,and achieve high-resolution applications.There are many methods for fiber laser to generate pulse modulation,but the preferred scheme is to use saturable absorber(SA)as the pulse modulation device of the laser cavity to realize the passive Q-switching or modelocked pulse output of the fiber laser.This is because the saturable absorber device has the advantages of excellent optical properties,simple preparation,strong versatility and small size,replacing the traditional expensive and complex active modulation.To be a proper SA,the key requirements for materials are fast response time,broad wavelength range,strong nonlinearity,low optical loss,high power handling,low power consumption,low-cost,and ease of integration into a laser system.This thesis focuses on the theoretical and experimental research of ultrashort pulse output based on SA passively mode-locked fiber laser.Antimony(Sb)and bismuth(Bi)effective SA,based on micro-nano fiber were prepared by magnetron sputtering deposition(MSD),and stable mode-locked operation was achieved in erbium-doped and thulium-doped fiber lasers.The main work is as follows:1.We introduced the development and preparation methods of saturable absorbers,and explain the characterization and integration methods of saturable absorbers.2.We introduce the transmission characteristics of optical pulses in optical fiber,including the effects of loss,dispersion and nonlinear effects on optical pulses.We use Maxwell equations to derive the basic propagation equation of optical pulse in optical fiber-nonlinear Schrodinger equation(NLS).We explain the mode-locking principle of mode-locked fiber laser,which provides a theoretical basis for experiments.3.Research on passively mode-locked fiber laser based on micro-nano fiber-Sb saturable absorber.Sb was deposited on micro-nano fiber by MSD method to prepare a kind of saturable absorber based on micro-nano fiber-Sb.The wide-band nonlinear optical properties were characterized by Z-scan system and balanced double detector method.The material properties were analyzed by Raman spectra,linear absorption spectra and XRD,and the film thickness was characterized by SEM.1.5 ?m erbium-doped fiber laser and 2 ?m thulium-doped fiber laser are built.Micro-nano fiber-Sb saturable absorbers are integrated into EDFL and TDFL respectively,and stable soliton mode-locked pulses of 544 fs and 972 fs are obtained.4.Research on passively mode-locked fiber laser based on micro-nano fiber-Bi saturable absorber.We prepared the saturable absorber based on micro-nano fiber-Bi by MSD method.We tested the Raman spectra,linear absorption spectra and XRD analysis of Bi thin films.The thickness and surface morphology of Bi thin films deposited on the surface of micro-nanofiber were characterized by scanning electron microscope(SEM).It is proved that the thin films prepared by MSD method have good uniformity.The nonlinear optical properties of Bi thin films and Bi SA were characterized by Z-scan system and balanced double detector method.The micro-nano fiber-Bi SA is integrated into 1.5 ?m EDFL and 2 ?m TDFL,and the modelocked pulses of 357 fs and 953 fs are obtained respectively.In this thesis,passively mode-locked fiber laser based on saturable absorber is studied theoretically and experimentally.The transmission characteristics of optical pulses in optical fiber and the basic principle of mode-locked fiber laser are analyzed,which provides a theoretical basis for the experiment.In the experiment,a new type of saturable absorber based on micro/nano fiber-antimony and bismuth was prepared by magnetron sputtering,and stable mode-locked pulse output was obtained in 1.5 ?m and 2 ?m wave bands.This technology provides a practical solution for the preparation of high-performance SA,is more likely to achieve large-scale production,and accelerates the development of new ultrafast fiber laser photon devices. |
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