Research On Erbium-doped Fiber Laser Based On Cuprous Sulfide Saturable Absorber

As an important scientific invention in human history,laser has changed all walks of life of human society,which is one of the greatest scientific inventions in the 20th century.Since Einstein put forward the concept of stimulated radiation in theory in 1917,in 1960,American scientist Theodore Harold Merman made the world's first laser,a ruby laser,based on the inspiration of microwave maser.It has been 60 years since the birth of the first laser in the world.In these 60 years,the development of laser is changing rapidly.At present,in many fields such as scientific research,industrial production,medical and health care,ranging communication and military application,there are all kinds of lasers playing their own role,promoting the development of human society.Fiber laser is a kind of laser with rare earth element doped glass fiber as gain medium.Shortly after the invention of the first laser in 1960,the first neodymium doped fiber laser came into being in 1961.However,due to the loss of glass fiber at that time,the development of fiber laser has been relatively slow.It was not until Gao Kun,a Chinese scientist,demonstrated the possibility of optical fiber communication in theory in 1960 and Corning company first developed low loss optical fiber in 1970 that fiber lasers ushered in a rapid development period.With the characteristics of high conversion efficiency,good heat dissipation,good beam quality and simple structure,fiber laser has become the mainstream direction of laser technology development and the main force of laser industry application.Using Q-switched pulse laser technology and mode-locked pulse laser technology can effectively shorten the pulse width and improve the peak power,so as to meet the pursuit of narrower pulse width and higher peak power in all walks of life.In the field of fiber laser,passive Q-switching and passive mode-locked technology based on saturable absorber are more popular.With the rapid development of fiber laser,the development of various saturable absorbers is also changing with each passing day.In recent years,with the continuous development of low dimensional materials,more and more low dimensional materials become the candidate materials of saturable absorbers because of their excellent photoelectric properties,and are widely used in fiber lasers.In this thesis,we focus on the novel two-dimensional material,cuprous sulfide nanosheets,and study the saturable absorption characteristics of cuprous sulfide nanosheets and the application of cuprous sulfide saturable absorber in erbium-doped fiber laser.As a copper-based Chalcogenide Semiconductor compound,the atomic structure of cuprous sulfide is different from the MX2 type structure of transition metal disulfide,but the nonlinear optical properties of two-dimensional layered cuprous sulfide deserve further attention.Cuprous sulfide has been widely used in many fields such as photoelectric conversion due to its excellent photoelectric properties.It is reasonable to believe that cuprous sulfide can also be used as saturable absorber in fiber laser due to its excellent nonlinear optical properties.In this paper,cuprous sulfide powder was prepared by alcohol thermal method,and cuprous sulfide nano sheet was prepared by liquid phase stripping method.The morphology of the prepared cuprous sulfide nanocomposites was characterized by a variety of characterization methods.Then,the copper sulfide saturable absorbers based on the end of optical jumper and the cuprous sulfide saturable absorbers based on the tapered fiber are prepared by using the cuprous sulfide nano chips.The saturable absorption characteristics of two kinds of cuprous sulfide saturable absorbers,such as modulation depth and saturation strength,were measured by a self-made double balance measurement system.The modulation depth of copper sulfide saturable absorber based on the end face of optical jumper is about 0.54%,and the saturation strength is 100.7 MW/cm2.The modulation depth of cuprous sulfide saturable absorber based on tapered fiber is about 0.48%,and the saturation strength is 263.3 MW/cm2.Finally,the Q-switched and mode-locked pulses with a central wavelength of 1530 nm are obtained by using the different copper sulfide saturable absorbers.When the pump power of erbium-doped fiber laser increases to more than 260 mW,the Qswitched pulse output can be realized due to the role of cuprous sulfide saturable absorber based on the end of optical jumper in erbium-doped fiber laser.The highest repetition frequency is 71.43 kHz and the narrowest pulse width is 2.58 ?s.When the pump power is more than 352.5 mW,a mode-locked pulse with a central wavelength of 1530 nm is obtained.The pulse width is 896 FS,the maximum peak power is 848 W.and the pulse energy is 0.76 nJ.In this paper,the application of cuprous sulfide in nonlinear optics and ultrafast photonics is explored.The Q-switched pulse output and femtosecond mode-locked pulse output based on cuprous sulfide saturable absorber are obtained for the first time.The good nonlinear optical properties and ultrafast optical properties of cuprous sulfide are demonstrated.It is proved that cuprous sulfide is still worthy of further exploration as a non-linear optical device and ultrafast optical device.At the same time,it also objectively promotes the development and application of two-dimensional metal sulfide materials in nonlinear optics and ultrafast photonics.