The Application Of Saturable Absorption Device Prepared By Sol-gel Method In Fiber Laser

The passively mode-locked fiber lasers in the near infrared region have a wide range of practical applications in optical communication,medicine,metrology and material processing because of their simple,compact design and good beam.Currently,semiconductor saturable absorber mirrors(SESAMs)are the most widely employed devices in industrial mode-locking lasers.However,SESAMs have some disadvantages,such as expensive semiconductors and special substrates coupled with mediocre flexibility.Fortunately,novel broadband SAs have recently been discovered,including carbon nanotubes,graphene,graphene oxide,transition metal sulfides,and others.Therefore,this paper focuses on the preparation of novel broadband saturable absorbers and their applications in fiber lasers.The damage threshold of saturable absorber is increased and the unsaturated loss is reduced by improving the preparation methods.the work is summarized as follows:First,we explore the experimental parameters of silica prepared by sol-gel method.The optimal ratio method of preparing SiO2 film is obtained by the control variable method after many experiments.Then,the GO-SiO2 SA is fabricated for the first time using low-temperature sol-gel technique.Scanning electron microscopy(SEM),annex-energy spectrometry(EDS),infrared spectroscopy(IR),and X-ray diffractometry identify the main component of prepared sol-gel glass as compact amorphous silicon dioxide.The application of GO-doped sol-gel glass to EDF laser yields stable mode-locked fiber laser operation.The pulse duration,maximum output power and peak power are recorded as 582 fs,17.58 mW and 1.30 kW,respectively.Generally,broadband absorbers has much non-saturable loss and low laser damage threshold,which limits the average output power of the fiber lasers mode locked by broadband absorbers.Therefore,it is important to increase the damage threshold of the broadband absorbers.In this study,a carbon nanotube(CNT)-doped sol-gel glass composite absorber is fabricated using a sol-gel method.The main component of the sol-gel glass is compact amorphous inorganic silicon-dioxide,which has high laser-damage threshold.The CNT-doped sol-gel glass is integrated into the erbium-doped fiber(EDF)laser and mode-locking occurs at 1559 nm.The shortest pulse duration is 456 fs,and the maximum average output power is 110.65 mW.Compared to most EDF lasers based on broadband absorbers,the average output power is one of the highest values.We demonstrate a nanosecond mode-locked erbium-doped fiber laser(EDFL)based on reduced graphene oxide(RGO)saturable absorber(SA).The RGO SA is prepared by depositing the graphene oxide(GO)on fluorine mica through thermal reduction of GO.Scanning electron microscope(SEM),Raman spectrometer and X-ray photoelectron spectroscopy(XPS)are adopted to analyze the RGO characteristics.The results show that the reduction degree of graphene oxide is very high.By embedding the RGO SA into the EDFL cavity,a stable mode-locked fiber laser is achieved with central wavelength of 1567.29 nm and repetition rate of 12.66 MHz.The maximum output power and the minimum pulse duration are measured to be 18.22 mW and 1.38 ns respectively.As far as we know,the maximum output power of 18.22 mW is higher than other nanosecond mode-locked oscillator reported.Such nanosecond pulse duration and megahertz repetition rate make this mode-locked erbium-doped fiber laser a suitable seed oscillator for high-power applications and chirped pulse amplifications.