Research On Ultrafast Fiber Lasers And Their Multiplexing

Serving as an ideal ultra-short pulsed light source,ultrafast fiber laser has played a significant role in telecommunications,precision measurement,micromachining and biomedicine due to its prominent merits of high efficiency,high pulse quality and compact design.Particularly,effective mode-locking techniques have greatly facilitated the development of ultrafast fiber lasers.Recently,the rise of two-dimensional materials saturable absorbers has propelled the advancement of mode-locked fiber lasers.Meanwhile,attributing to the fertile intra-cavity physical mechanisms,different solitons can be formed by proper lasing configuration.Developing multiplexed ultrafast fiber lasers delivering multi-state solitons,and thus meet diversified demands has been attached great importance by the research community.In this dissertation,we investigate multiplexing schemes and key devices——saturable absorbers towards passively mode-locked fiber lasers.Based on different mode-locking techniques,we develop two multiplexed ultrafast fiber lasers,in which the multiplexing of soliton singlets and molecules is realized,as well as the multiplexing of conventional and dissipative solitons.The main contents of this dissertation include:(1)Two-dimensional materials based all-fiber saturable absorbers.By ultrasonic-assisted liquid-phase exfoliation,we prepared single-layer two-dimensional WS₂ nanosheets,and then fabricated two kinds of saturable absorbers based on tapered fiber and suspended-core fiber,respectively.The modulation depths of these two mode-lockers are 3.0%and 3.3%,respectively.(2)Soliton singlets and molecules multiplexed ultrafast fiber laser.To start with,we investigated the simulation principle of soliton molecules based on the primary mathematic relationships.Then,various soliton molecules with different pulse assembling forms were studied via a saturable absorber mode-locked laser.Tightly and loosely bound soliton molecules,as well as sextuple and octuple bound soliton molecules were separately observed.Up to 35^thharmonic mode locking and the pulse energy quantization were also demonstrated.Furthermore,the coexistence of soliton singlets and molecules was realized via dual-wavelength mode locking,where the multiplexing between soliton singlets and evenly/unevenly spaced molecules were analyzed respectively.The pulse intervals,number and distribution could be manipulated with appropriate adjustments.(3)Conventional and dissipative soliton multiplexed ultrafast fiber laser.Trough developing a bidirectionally mode-locked lasing cavity,different dispersion distributions were introduced into a common oscillator,and conventional and dissipative solitons were thus generated in clockwise and counter-clockwise propagations simultaneously.Here,we proposed two multiplexing schemes using 2-m dispersion compensation fiber and a chirped fiber Bragg grating,where conventional and dissipative solitons with the pulsewidth of 646 fs and 428 fs,and 3.96 ps and 8.17 ps are delivered,respectively.Meanwhile,wavelength tuning and multi-wavelength operations of solitons and noise-like pulses with ranges of 42 nm and 35 nm were also achieved via birefringence filtering effect.