Research On The Mode-locking Mechanism And Experimental Technique Of All Fiber Lasers

Along with the rapid development of science and technology,people's ability to observe and understand the material world is more and more super,so the requirements for the used tools are increasingly high.And the development of ultra-short pulse source has a major impact on the progress of the scientific technology,which makes it possible to direct observe some of the fastest process in nature.At present,the researchers are trying to approve the time resolution in ultra-fast regime to attosecend?10-18s?scale and developing the regime of X-ray detection.At the same time,people are trying to apply the ultrafast laser technology to more broader social domain,and the technical progress is always depending on the availability and stability of the ultrashort optical pulse source.However,in recent years,the development of optical fiber laser is varying rapidly and a large number of results have been obtained.Moreover,the fiber laser exhibits unique advantages in many aspects,such as low cost,easy integration,rich working modes,and so on.Just under this background,based on the all fiber ultrashort pulses laser,this thesis researches the relationship between the dispersion distribution of fiber laser and the output pulses characteristics,furthermore,we design new saturable absorber device incorporating with new materials and apply it to all fiber mode-locked laser.The main substances discussed in this study are arranged as follows:1.In the passively mode-locked all fiber laser,we research the formation mechanism,theoretical model,laser dispersion distribution,implementation method,pulse time domain and frequency domain characteristics,and energy levels of conventional solitons,stretched pulses,self-similar pulses,and dissipative solitons.2.We research the theoretical model and numerical simulation results of dissipative soliton resonance,and summarizes the definition of dissipative soliton resonance.By quoting the others experiment of dissipative soliton resonance in an normal-dispersion fiber laser,we summarizes the performance characteristics of dissipative soliton resonance on experiment: the pulse spectrum shows Gaussian profile and the temporal envelope is rectangular;with the increase of pump power,the pulse spectral width remains unchanged while its intensity increases monotonically,the intensity of the temporal envelope keeps unchanged while its width width increases monotonically.According to the nonlinear polarization rotation technique,through the reasonable design of the experiment and the unremitting adjustment of dispersion parameters in experimental,we explore and successfully observe the phenomenon of dissipative soliton resonance in an anomalous-dispersion fiber laser,which fills a gap in international,and overturn the traditional concept that the dissipative solitons can only exist in an normal dispersion laser.The results also demonstrate that the fiber laser with a negative dispersion can also output a high energy pulse.3.We studied the saturable absorption characteristics of carbon nanotube and compare it with other types of saturable absorber materials,further highlight the excellent properties of carbon nanotubes.We made the SWCNT/PVA?single wall carbon nanotubes/polyvinyl alcohol?films,and make it to be user-friendly saturable absorber device.Moreover,we measure the saturable absorption characteristics of this device though a self-made mode-locked fiber laser.Furthermore,we design an Yb-doped fiber laser and realized dissipative soliton mode locking at the wavelength of 1051 nm by the self-made SWCNT saturable absorber device,the pulse sequence is stable and uniform and the signal to noise ratio is higher than 60 dB.And then we design an amplifier system,the pulse energy is amplified to 93 nJ,the pulse width is measured as 421 ps,and the pulse profile can be determined to be Gauss type in time domain.At last,we set up a theoretical model and numerically simulate the mode lock process of fiber cavity.4.We study the saturable absorption properties of new materials Bi₂Te₃ and MoS₂,and combine them respectively with the two methods of making absorber device though evanescent wave method?fiber taper and D-shaped fiber polish?.Though reasonable design of the device and resonator,the former one realizes mode locking output of traditional soliton,and the later one realizes mode locking output of conventional soliotn and dissipative soliton at the same time.We describe the experimental process in details and analyze the experimental results meticulously,then compare the results with the other research' results.And we found that the former one has improved the signal to noise ratio obviously and the latter one lower the inserting loss from ⁷5% to ¹3% which makes the laser stating threshold lowered to several milliwatt.Finally,we expound the significance of the experimental: it provides an efficient scheme for the design of high performance saturable absorber device.5.We put forward on making the mica substrate as the substrate of the absorber film and highlight the advantages of this method;it could avoid the damage of low damage threshold,large inserting loss,and poor mechanical performance.We study the process of growing graphe and WS₂ on the surface of fluorphlogopite mica.And then we apply this device in fiber laser and successfully obtain mode locking output,which proves that this kind of saturable absorber producing method is feasible.It provides a feasible design scheme for producing high damage threshold and low inserting loss absorber device.At last,we summary the superiority of this absorber device manufacturing method,set up some existing problems,and give suggestions on the further improvement.