Preparation Of MnO₂ Saturable Absorber And Wide-band Luminescent Rare Earth Ions Doped NaYF₄ Nanoparticles For Optical Communication

With the development of optical communication towards large capacity and high speed,the development and upgrading of various optical devices have attracted extensive attention of researchers.Therefore,with the rapid development of nanotechnology,a variety of new nano optical materials to improve the performance of devices are constantly emerging.The saturable absorber is the key component of the passively modulated pulsed fiber laser.Nanomaterials with two-dimensional structure are preferred as saturable absorbers because of their wide band saturation absorption characteristics,ultrafast carrier dynamics,short photobleaching recovery time and other properties,and it plays an important role in the construction of novel passive Q-switched pulse laser systems.However,some two-dimensional nanomaterials that have been used as saturable absorbers in passively modulated pulsed laser systems still have some shortcomings in performance,and it is urgent to develop new two-dimensional nanomaterials to further improve the performance of saturable absorbers.For example,graphene has a low depth of modulation;The preparation process of two-dimensional topological insulators is complicated.Most layered transition metal dihalides have large band gaps and need complex defects regulation,so they should not be used as saturable absorbers.Black phosphorus has poor chemical stability and is easily oxidized in the air.Therefore,in order to develop high quality Q-switched pulse lasers,we have been working on exploring new two-dimensional saturable absorbers with high performance.Because of its suitable band gap,high third-order nonlinear coefficient,good stability and excellent electrical and optical properties,the two-dimensional ultra-thin laminated Mn O₂ nanosheet material is suitable for the preparation of saturable absorbers.In addition,as an integrated optical amplifier,lanthanide doped polymer optical waveguide amplifier plays an important role in the miniaturization and integration of communication systems.As a gain medium,lanthanide doped materials can obtain relatively high gain in optical amplifiers,so they have been widely studied in the field of integrated optical communication.At present,because the optical amplification wavelength of erbium-doped optical amplifier is located in the C+L band,which is in the working band of optical communication,the erbium-doped optical waveguide amplifier(EDWA)has been widely studied.However,with the explosive growth of network communication demand,how to expand the working wavelength of optical amplifier has become a research hotspot.The S+C+L+U band can be covered by the doping of erbium and thulium,which meets the need of using lanthanide doped materials as gain medium to fabricate broadband optical amplifier.Therefore,the design and preparation of erbium and thulium co-doped nanoparticles have been studied.To explore the concentration and proportion of lanthanide ions with different luminescence peak locations to achieve wide-band luminescence of nanoparticles,and to expand the effective bandwidth of gain media.In this paper,we studied the nanomaterials needed for the above two kinds of photonic devices,and obtained the manganese dioxide saturable absorber material for Q-switched laser and erbium-thulium co-doped NaYF₄ nanomaterials for organic optical waveguide amplifier as gain medium.Specific research contents are as follows:(1)In order to explore the new saturable absorber to achieve the output of Q-switched pulse in multi-band,we studied the saturable absorber of manganese dioxide nanosheets.Firstly,Mn O₂ nanosheets were prepared by REDOX reaction.Then,Mn O₂ solution was reacted with sodium carboxymethyl cellulose to form a film.Finally,the reactant was coated on the quartz slide substrate and dried to obtain the saturable absorber of Mn O₂ nanosheets.The morphology and nanostructure of Mn O₂nanosheets were studied by means of electron microscopy:TEM,SEM and HRTEM.The distribution of elements in the nanosheet was determined by EDX spectrum.The absorption spectra of Mn O₂ nanomaterials were measured.It was found that the light absorption of Mn O₂ nanomaterials was wide in the near infrared region(800?2200nm).In order to verify the Mn O₂ saturated absorption characteristics of nano film,the nonlinear propagation characteristics of saturable absorption thin films in Mn O₂nanosheets have been studied by using an Erbium-doped pulsed fiber laser.A stable Q-switched laser pulse with a central wavelength of 1558 nm,a maximum pulse repetition frequency of 92.35 k Hz,a maximum output power of 17.18 m W,a minimum pulse width of 1.26?s and a signal to noise ratio of 45 d B has been obtained.The results show that Mn O₂ nanosheets are excellent saturable absorbers for Q-switched pulse laser generation.(2)In order to obtain nanomaterials with wide broadening,uniform size and good dispersion in the near infrared band,we doped the activator erbium ion covering band C,the activator thulium ion in band S and L by infrared luminescence,and the sensitizer ytterbium ion into the NaYF₄ matrix material with high luminescence efficiency in a certain proportion.Therefore,two series of Er-Tm co-doped NaYF₄nanoparticles with different concentrations,NaYF₄:20%Yb,0.1%Er,x%Tm and NaYF₄:20%Yb,1%Tm,y%Er,were prepared by high temperature thermal decomposition method.TEM was used to characterize the morphology and size of the nanoparticles,and it was found that the morphology of the prepared nanoparticles was relatively uniform,the crystal size was about 25 nm,and the dispersion was good.The prepared nanoparticles were all hexagonal phase by XRD.By adjusting the concentration and doping ratio of Tm³⁺and Er³⁺ions,the down-conversion emission spectra of the samples were measured under the excitation of 980 nm laser,and it was found that the emission intensity and half-high full width(FWHM)of NaYF₄:Yb,Tm,Er increased firstly and then decreased with the increase of Tm or Er ion concentration.When the concentration ratio of Tm and Er is 10:1,the FWHM of spectrum is 75 nm larger than that NaYF₄:Yb,Tm and NaYF₄:Yb,Er.This will be of great significance in the future research of using this nanomaterial to fabricate polymer gain medium in optical waveguide amplifiers to achieve all-optical amplification and short-range communication band broadening.