Study On DBR Single-frequency Pulsed Fiber Laser Technology In 2.0 ?m

Single-frequency pulsed fiber lasers near 2.0 ?m have attracted considerable attention in coherent detection,high-resolution spectroscopy,nonlinear frequency conversion,gravitational wave detection and medical treatment.Compared with continuous lasers,2.0 ?m singlefrequency pulsed lasers have higher peak power and single pulse energy.The laser with temporal flexibility,in which repetition frequency and pulse width can be flexibly regulated,can be used for practical applications.However,there are little research on 2.0 ?m singlefrequency pulse with stable output laser,high peak power and high pulse energy in the ultrashort cavity currently,which limits its further applications in lidar and so on.After introducing the related technologies and research progress of single-frequency pulsed fiber laser,combining with the technology of DBR ultra-compact cavity,theoretical and experimental researches on passively Q-switched and gain-switched technology is implemented.The contents and results of specific research on 2.0 ?m DBR single-frequency pulsed fiber lasers are as follows:(1)Based on the absorption and emission spectrum and energy level of thulium ions,its particle transition process is discussed.The theoretical models of the rate equation of the passive Q-switching technique in the cavity and the gain switch are established respectively.The formation mechanism and dynamic characteristics of the pulse are analyzed theoretically.The experimental factors which affect the characteristics of the output pulse are discussed.The difference between the intracavity Q-switched and the gain-switch technology is compared.(2)Based on passively intracavity Q-switched technology,a semiconductor saturable absorption mirror(SESAM)is used to replace the high-reflection fiber Bragg grating in the DBR laser cavity.A 1950 nm passively Q-switched single-frequency pulsed fiber laser with an output power of 22.2 m W and maximum peak power of 0.67 W is achieved.The repetition rate and pulse width of the pulsed laser can be regulated from 92 to 520 k Hz,64 to 221 ns,respectively.Besides,comparing three different SESAMs,the influence of SESAMs' parameters such as reflectivity and modulation depth on output pulse is obtained.Furthermore,a dual-wavelength single-frequency pulsed fiber laser is realized by employing a polarizationmaintaining high-reflection fiber Bragg grating in the DBR short cavity,the center wavelengths of which are 1949.33 nm and 1949.83 nm,respectively.(3)Based on gain-switched technology,a 1610 nm semiconductor laser(LD)directly modulated by the current is used as the pump pulse seed source.After two stages of amplification,the in-band pumped DBR single-frequency laser resonator is used with a 16 mm thulium doped germanate gain fiber.A 1950 nm single-frequency pulsed fiber laser with a tunable repetition rate of 1?500 k Hz and an average power of 111.8 m W is obtained.Under the condition of a repetition rate of 100 k Hz,the narrowest pulse width of 19 ns and the highest peak power of 34.2 W is achieved.Further,a hybrid pumped gain-switched fiber laser was proposed,in which a hybrid laser composed of a 793 nm continuous pump laser and a 1610 nm pulsed pump laser is used to pump the single-frequency DBR laser cavity.A single-frequency pulsed fiber laser with higher pump efficiency of 12.7% and higher pulse energy of 251.6 n J is achieved.