Study Of Pulsed Fiber Laser Based On Gold Nanorods And Copper Sulfide Nanoparticles Saturable Absorbers

Pulsed fiber lasers have the advantages of compact structure,good environmental stability and low cost.At present,the pulsed fiber lasers have a wide range of applications in fields of optical fiber communications,medical surgery,industrial welding,industrial cutting,and defense space confrontation.Saturable absorbers are key components of passively pulsed fiber lasers.At present,commonly used saturable absorbers are semiconductor saturable absorber mirrors(SESAMs),carbon nanotube saturable absorbers(CNTs),and two-dimensional material saturable absorbers.For the first time,our experimental group utilized the optical properties of surface plasmon resonance absorption of gold nanomaterials to achieve pulsed fiber lasers.At the same time,gold nanomaterials also have the advantages of higher third-order nonlinear coefficient,ultra-fast response time,low fabrication cost,etc.It is considered as an ideal saturable absorber material.However,gold nanomaterials have a strong photothermal effect.When operating for a long time or when operating in high power lasers,the photothermal effect can cause the material to be damaged,which shortens the life-time of the saturable absorber.Therefore,it is meaningful to improve the structure of gold nanorod saturable absorbers and explore new types of saturable absorbers.During master's degree,the authors conducted a systematic study around pulsed fiber lasers based on gold nanorods and copper sulfide nanocrystal saturable absorbers.The research results are as follows:(1)A large number of studies have found that there is an evanescent field effect in the tapered fibers,and the interaction between the evanescent field effect and the material also has the same properties as the saturable absorber.This structure can reduce the heat accumulation caused by the photothermal effect.Based on the above theoretical basis,the authors proposed a saturable absorber device in which a tapered optical fiber and a gold nanorod are composited.The composite saturable absorber was fabricated experimentally,and the output of mode-locked pulsed laser was successfully realized in erbium-doped fiber lasers.The pulse width was 404 fs;the repetition rate was 25.66 MHz;and the maximum output power was 45.53 mW.This result has a performance improvement of about 8 times as compared with the maximum output power of the mode-locked pulse laser realized by the gold nanorod saturable absorber using the sandwich structure.(2)The study found that the copper sulfide nanocrystal material also has localized surface plasmon resonance properties,which is similar to the properties of gold nanorods.Compared with gold nanorods,the size of copper sulfide nanocrystal material is smaller,about 10 nm.The small size can effectively reduce the photothermal effect,which is conducive to the long-term stable operation of saturable absorbers.It is also conducive to achieving higher power pulsed fiber laser.Based on the above studies,the authors proposed an experimental scheme for the use of copper sulfide nanocrystals as saturable absorbers to achieve pulsed laser output.In the experiment,copper sulfide saturable absorber films were fabricated using sodium carboxymethyl cellulose as a film former,and a Q-switched erbium doped fiber laser with a wavelength of 1.56 ?m was developed.Compared to the gold nanorod saturable absorber,in order to verify that the damage threshold of the copper sulfide nanocrystal saturable absorber is greatly improved,we tested the samples with the same concentration and the same thickness.The test results show that,under the same conditions,the maximum output power of a Q-switched laser based on a copper sulfide nanocrystal saturable absorber is 3 to 4 times the maximum output power of a Q-switched laser based on a gold nanorod saturable absorber.