Research Based On Magnetic Fluid Saturable Absorber Erbium-doped Fiber Laser

A Pulsed laser has a wide range of applications in optical fiber communication,medical instrument and equipment,large-scale infrastructure,military defense security,laser marking,laser cutting and so on.It has the advantages of compact structure,good quality of beam and light pulse.Compared with the actively Q-switched laser,the passively Q-switched laser has the advantages of compact structure,easy realization of all-fiberized,relatively low cost,simplified operation and so on,and can obtain shorter pulse,get more repetition frequency.In the passively Q-switched fiber lasers,the most critical factor is the saturation absorption effect of materials and devices development and application.As the traditional saturable absorber?such as Semiconductor saturable absorber mirror,etc.?exists complex production process,expensive and other defects,limiting the development of pulsed lasers.And this promotes researchers to explore new materials.Later new nanomaterials?such as carbon nanotubes,graphene,topological insulators,transition metal dichalcogenides,magnetic fluids,etc.?continue to emerge,these new materials have their own unique optical and electronic properties,become the current research hot spots.Recently,the new nano-functional material,magnetic fluid has also attracted the attention of researchers,due to its limited size,surface effects with large optical nonlinearity and a large relaxation time,indicating pervasive applications in the pulse laser.In this thesis,we fabricate and characterize a new type of magnetic fluid SA.Employing this SA,we construct variety Q-switched operation in the erbium-doped fiber laser.The main work of this paper is as follows:1.We introduce pulsed fiber lasers and the advantages of pulsed lasers relative to traditional bulk solid-state lasers,the advantages of passively Q-switched fiber lasers with respect to actively Q-switched and the classification and advantages of different passive Q-switched fiber lasers,research progress of Q-switched fiber lasers with saturated absorbers.We also highlight the historical evolution of the SA applied to Q-switched fiber laser.2.We briefly describe the Q-switched principle and introduce the magnetic fluid and analyze the magnetic fluid saturable absorber principle.By using a Raman spectrometer,three characteristic peaks of magnetic fluid is located at 284 cm^-1,490 cm^-1 and 695 cm^-1.The transmittance of the magnetic fluid film was measured by using an optical spectrometer.It is measured that the absorption of the film is 32.8% at 1560 nm.In the end,we test the intensity-dependent optical absorption of the SA.The modulation depth,saturable intensity and nonsaturable loss are measured to be 11.3%,98.15MW/cm2,and 19.83%,respectively.3.Based on the magnetic fluid single-wavelength Q-erbium-doped fiber laser experiments: we use spin-coating method to coated magnetic fluid solution between the optical fiber connector,and through the flange fixed to prepare sandwich saturable absorber.We obtain Q-switched pulse in EDFL.The measured signal-to-noise ratio of Q-switched pulse is 54.4dB,the center wavelength of the spectrum is near 1558.4nm,and the bandwidth of 3dB is about 1.8nm.When the pump power is 550 mW,the maximum average output power obtained is 41.2mW and the maximum single pulse energy is 321.3nJ.4.Based on magnetic fluid multi-wavelength Q-switched erbium-doped fiber laser: We briefly introduce multi-wavelength laser features and the several methods to realize multi-wavelength laser.In this experiment,a multi-wavelength erbium-doped fiber ring laser was fabricated by adding a Mach-Zehnder interferometer in the cavity and magnetic fluid as a saturable absorber.The experimental results show that the EDFL can be achieved.The Q-switched fiber laser has 18 wavelengths at the same time.When the pump power increases from 30 mW to 340 mW,the repetition frequency of the output pulse increases from 9.83 k Hz to 53.24 kHz,the single pulse energy increases from 8.32 nJ to 117.62 nJ,and the pulse width decreases from 3.9?s to 1.01?s.5.Based on the magnetic fluid tunable Q-switched erbium-doped fiber laser experiment: By adding magnetic fluid SA and tunable filter in the cavity,we obtain a stable Q-switched pulse in EDFL.The operation wavelength can be continuously tuned from 1513.14 nm to 1564.70 nm at a fixed pump power.