Study On Thulium-doped Fiber Laser And Its Application In All-fiber MIR Supercontinuum Generation

Fiber laser is regarded as one of the most promising laser sources because of its essential characteristics such as compact configuration,high beam quality,high conversion efficiency,excellent thermal performance,and it is easy to achieve high power output.Fiber laser has significant applications in scientific research,industrial production,medical treatment and military.Researches on 2 ?m thulium-doped fiber(TDF)lasers have attracted worldwide attention,especially high power pulsed TDF lasers,TDF-based Ramam fiber lasers,and mid-infrared supercontinuum sources at 2-5 ?m wavelength.With rapid development of 2 ?m fiber optic devices,the output indicators of the 2 ?m TDF lasers are also improving rapidly.The maximum average output power of the TDF laser is 1050 W,nanosecond and picosecond pulsed average output power have also reached the hundred-watt level.It is worth noting that femtosecond chirped pulse amplification has also achieved ultra-high peak power > 5 GW.This dissertation mainly focuses on the nanosecond and picosecond pulsed TDF oscillator,high power TDF amplifier,and all-fiber mid-infrared supercontinuum sources at 2-5 ?m wavelength.First,the nanosecond pulsed TDF is achieved via nonlinear amplifying loop mirror(NALM)technique and the amplification characteristics are studied.Then,passively mode-locked picosecond pulses are generated by a SESAM-based TDF laser.Amplification characteristics and supercontinuum generation are also discussed.Last,in order to achieve the real all-fiber format mid-infrared supercontinuum source,the effective thermal splicing method to join fluoride and silica fibers is studied.The main contents with novelties are as follows:1?Dissipative soliton resonance(DSR)is demonstrated by utilizing a compact,all-fiber figure-of-9 double-clad TDF laser.The mode-locked rectangular-shape pulses are achieved by using NALM technique.The obtained maximum average output power and pulse energy are 41.5 mW and 130.5 nJ,respectively.Characteristics of the amplified DSR pulses are also studied by using a three-stage MOPA system.The output power and pulse energy are scaled to 104.3 W and 0.33 mJ,respectively.To the best of our knowledge,this is the highest single pulse energy of the DSR pulse.2?A mode-locked TDF laser with dual operation regimes is presented.The mode-locking is initiated by using a commercial SESAM in a typical linear cavity and could operate at both fundamental mode-locking and noise-like twin-pulse regimes.Then,the mode-locked TDF laser is amplified by a two-stage MOPA system,and used to pump a segment of highly Ge-doped nonlinear fiber.Cascaded Raman light and supercontinuum generation are obtained respectively.At the fundamental mode-locking regime,two orders of stokes light can be generated,centered at 2.13 and 2.35 ?m,with a maximum total power of 3.75 W;At the noise-like pulse regime,a near-infrared supercontinuum from 1.93-2.46 ?m is generated with a maximum average output power of 2.5 W.By optimizing the structure of the amplifier and the length of nonlinear fiber,the output spectrum can be further extended to 3 ?m and the output power up to 11.62 W.To the best of our knowledge,this is the highest average output power ever reported for a supercontinuum source based on a highly Ge-doped fiber.3?Low loss splice between fluoride and silica fiber are achieved by utilizing glue splicing method and thermal splicing,respectively.It has been found experimentally that the thermal splicing method is more suitable for high power regime.The power capacity of the splicing joints is also tested with a high power fiber laser.The measuring results show that the splicing joints can withstand optical power up to 15 W.An integrated all-fiber mid-infrared supercontinuum source is generated by a high power 2 ?m picosecond fiber MOPA system and a segment of single-mode ZBLAN fiber.The maximum average output power is 10.67 W with spectral bandwidth covering from 1.9-4.1 ?m.It is,to the best of our knowledge,the first 10 W-level integrated compacted all-fiber mid-infrared supercontinuum source based on thermal-spliced silica fiber and ZBLAN fiber.