Research On 1.6 μm Erbium/Ytterbium Co-doped Fiber Laser

In recent years,as the air pollution is becoming more and more serious,the atmospheric monitoring is becoming crucial.Light detection and ranging(LIDAR)has been paid more attention as an efficient method of the atmospheric monitoring.With the widespread application of the LIDAR,the requirement of the laser is becoming stricter.The laser is expected to have high output power,excellent beam quality,durable and the working in the eye-safe band.The 1.6 μm erbium/ytterbium co-doped fiber laser(EYDFL)exactly meets these requirements.Firstly,the erbium/ytterbium co-doped fiber(EYDF)is working from 1535 nm to 1620 nm,and 1.6 μm belongs to this range.Secondly,1.6 μm is within the eye-safe band,and has good penetration ability to smoke,suitable for working in the haze weather.Finally,all-fiber lasers are high-efficient,compact,cost-effective and easy to maintain.There are two structures of all-fiber laser,one is to use fiber bragg gratings(FBGs)and doped fiber as the laser cavity,the other is to amplify the seed light.In this paper,two structures of 1.6 μm EYDFL are studied by simulation and experiment.The specific work is listed as follows:1.The background and development history of the EYDFL have been investgated.The reasons for limiting the power increase of the EYDFL have been analyzed and the solutions have been proposed.The energy level structure of the EYDF has been analyzed,and the rate transmission equations have been derived,with calculation formulas in detail.2.Numerical simulation: Firstly,the power transmission equations of the FBG structure based on the forward-pumping structure have been deduced.The reflectivity of the FBGs and the length of EYDF have been optimized by numerical simulation.Then,according to the hybrid-pumping structure,the distribution of the pump power and the doped fiber length are optimized.Secondly,the power transmission equations of the forward-pumping structure of master oscillation power amplification(MOPA)are derived.The distribution of the signal power and the pump power in an EYDF is numerically calculated.The best EYDF length and the input signal power are obtained.Thirdly,based on the three basic pumping structures and the two-stage amplification,the relationship between the output power,the gain,the amplified spontaneous emission power and the pump power have been compared by simulation.The best MOPA structure is the two-stage amplifier structure.3.Experiments: Firstly,for the laser with the FBG structure,the length of EYDF is2.6 m and 2.4 m,respectively.The obtained laser wavelength is 1599.6 nm,with the 3-d B bandwidth of 0.06 nm,the output power of 800 m W,and the side mode suppression ratio of 21 d B.Secondly,for the two-stage MOPA structure.,the length of EYDF is 5 m and 5.4m,respectively.The center wavelength of the amplified signal light remains unchanged at1588.8 nm.The bandwidth is slightly expanded to be 0.0765 nm.The laser has a output power of 5 m W,the overall gain of 21 d B,the repetition frequency of 100 μs and the pulse width of 2 μs.