Investigation Of Short-straight Cavity Single-frequency Fiber Laser And Temperature Sensitivity Enhancement Of Fiber Bragg Grating Sensor

In recent years,single-frequency fiber lasers have developed rapidly as a research hotspot in the field of lasers.Because of its good coherence,easy integration,good heat dissipation,good beam quality and strong anti-interference ability,it is widely used in laser ranging,laser radar,fiber-optic hydrophone,laser medical,interference detection,spectral imaging,gravitational wave detection fields.With the rapid development of new technologies for highly-doped and multi-component glass fibers,the choice of single-frequency output cavity in the field of fiber lasers is increasingly biased towards short linear cavities,with simple and compact structure,all-fiber,high stability,large longitudinal mode spacing and difficult to jump mode,so that the method of realizing the single-frequency output of fiber lasers with distributed bragg reflector?DBR?short-straight cavity structure has been actively concerned and researched by researchers.In this paper,two HR-FBG and 1.4cm-length high-doped Yb³⁺gain medium are used to construct the DBR short-cavity fiber laser,and the single-frequency laser output with output wavelength of 1030nm is successfully realized.And an experimental study on the amplification of its output power.At the same time,the fiber Bragg grating?FBG?local point heating bandpass filtering characteristics and temperature sensitivity enhancement characteristics were also studied experimentally.The main research contents and results of this paper are as follows:Firstly,the transfer matrix theory is briefly introduced,and the influence of different phase mutations introduced into different positions of the FBG gate region on its reflection spectrum is theoretically calculated and analyzed.On this basis,based on the transfer matrix theory,the parameters such as heating temperature,heating position and heating width were changed,and the output spectral characteristics of FBG local point heating were theoretically analyzed.In addition,the energy level structure and spectral characteristics of the doped Yb³⁺ion fiber were introduced and analyzed.Next,a single-frequency fiber laser based on two wide-band,high-inverse-fiber grating?HR-FBG?short-cavity DBR structures is proposed.The short straight cavity DBR fiber laser uses a 1.4 cm long quartz glass substrate and a high doping concentration Yb³⁺gain fiber as the working medium.By precisely temperature control the two HR-FBGs of the fiber laser,the edges of the reflection peaks are overlapped,thereby effectively narrowing the gain bandwidth in the cavity,and the single longitudinal mode laser output with an output wavelength of 1030nm is successfully realized.And a comprehensive experimental study of its operating characteristics.The fixed output HR-FBG temperature is 12°C,and the input HR-FBG temperature is in the range of 59.2°C⁶0.6°C.The DBR short straight cavity fiber laser always exhibits single longitudinal mode operation.At the same time,when the fiber laser is in single longitudinal mode operation,the two HR-FBGs are simultaneously temperature-tuned according to the same temperature step,realizing a continuously tunable single-frequency laser output.In order to realize the high power output of the single-frequency fiber laser,an experimental study of the backward pump light amplification method was separately performed on the single-frequency laser output.Under the condition of this power amplification mode,when the gain length is 8.5 cm,the obtained amplified output power is 349.7 mW,and the oblique efficiency is 69.8%.Based on this work,the output spectral characteristics of broadband FBG under localized point heating are experimentally studied,and single-wavelength,dual-wavelength and four-wavelength filtering windows are realized.The fiber laser single frequency composed of double-bandwidth HR-FBG is realized.The output provides a possible method.Finally,The enhanced temperature sensitivities of Fiber Bragg Gratings?FBGs?slice-packaged with copper,aluminum,perspex and PTFE are studied experimentally.The results show that when the coated fiber tails on both sides of FBG are bonded on substrate materials,the temperature sensitivity coefficients are about 2.3 times,2.9 times,5.2 times,and 11.7 times that of a bare FBG,respectively.For experimental optimization,the experiments under the uncoated tail of FBG are carried out based on the aforementioned four substrate materials.The reflection wavelengths have a good linear relationship with the temperature change within the measurement temperature range.The temperature sensitivity coefficients of FBGs are enhanced to 3 times,3.4 times,9.2 times,12.6 times,respectively,and the results show a good measurement reproducibility.