Research On The Characteristics Of Ultrashort Laser Pulses Based On Lead Sulfide Nanoparticles

Ultra-short pulse lasers have good optical properties and can be used in industrial,medical,military and other fields.Lasers are a direct and effective method of generating laser pulses.Because fiber lasers have the advantages of simple and flexible structure,low cost,and fast heat dissipation,so they have stood out in the field of laser research and have been receiving much attention.With the development of modern optical fiber communication,in order to further improve optical communication capabilities,wavelength division multiplexing(WDM)communication systems are developing to more and more channels,it has become the most economical and effective way to achieve the upgrade and expansion of fiber optic communication systems.The most direct way to provide multi-channel optical signals is to use multiple single-wavelength lasers.However,simply increasing the number of light sources will inevitably increase costs,so the excellent performance of dual-wavelength or even multi-wavelength fiber lasers is more optimistic.Multi-wavelength lasers can simultaneously provide optical signals for multiple channels,which greatly reduces the cost of optical transmitters and has important application value in WDM systems.Saturation absorption technology is one of the most important technologies for fiber laser mode-locking to achieve ultra-short optical pulses.Therefore,finding excellent saturable absorber materials has been a research focus in recent years.Lead sulfide nanoparticles(PbS NPs)exhibit excellent ultrafast photonics performance in communication systems due to their narrow band gap,high thermal damage threshold,and stability.In this paper,we use PbS NPs as a new type of saturable absorber in erbium-doped fiber lasers,and finally successfully achieve pulse output with different characteristics.At the same time,this experimental study also opens a new path for the research of fiber laser passive mode-locking in saturable absorber.The main work of this thesis:(1)The first chapter introduces the development history of lasers and the mechanism of laser pulse formation in passive mode-locked fiber lasers.On the other hand,the research progress of new nanomaterial saturable absorber devices is also given.(2)The main content of Chapter 2 is around the preparation and characterization of saturable absorber of PbS NPs.Firstly,several preparation methods of PbS NPs are introduced,including liquid-phase synthesis method(wet chemistry method),precipitation method,precursor pyrolysis method,and sol-gel method.Preparation method(light pulse deposition method).Finally,we performed a series of measurements and characterizations on the optical properties of PbS NPs.(3)The third and fourth chapters mainly study the application of saturable absorber based on Pbs in passive mode-locked fiber lasers.We inserted the Pbs NPs saturable absorber device into an erbium-doped fiber laser cavity to achieve the traditional soliton mode-locked laser pulse.In the previous experiments,typical spectra of traditional solitons with a center wavelength of 1533 nm were obtained.After that,we continued to try to change the cavity length and optimize the material preparation process.Based on the previous work,we achieved better results,and produced dual-wavelength picosecond-level short pulses that can occur simultaneously or separately,with the center wavelengths of 1545 nm and 1585 nm.It is worth mentioning that the two wavelengths are separated by 40 nm,covering the C-band and L-band of the communication area,which significantly increases the optical communication capacity.Our new work not only achieved the effect of dual-wavelength mode-locking,but also obtained ultra-short pulses of 1.31 ps.(4)The fifth chapter summarizes the main research contents and results of this thesis and elicits the problems that need to be solved at present,and finally looks forward to the follow-up work.