Research On Splicing And End Facet Handling Technology Of Large-mode-area Photonic Crystal Fiber In High Power Fiber Lasers

In recent years,fiber laser has become one of the hottest points in the field of laser research.However,the output power is higher and higher with the development of the fiber technology,which causes the physical mechanism like nonlinear effect,thermal injury,etc.The large-mode-area photonic crystal fiber(PCF)has the characteristics of large-mode-are and single-mode operation without cut-off,which can solve the problem of nonlinear effect caused by too much high power density.Nevertheless,recently,Free-space couple is the most common method when the large-mode-area PCF is used in the high power fiber lasers.In this thesis,we have used a kind of double-clad large-mode-area of 500 ?m outer diameter PCF produced by NKT as the object and discussed how to handle it for achieving ideal laser quality in the high power fiber laser.The main contains are list as follows.1.An effective method of stripping and flat cutting of the large-mode-area PCF was demonstrated.The chemical liquid stripping can avoid the damage of the fiber as much as possible.The cleaver of Vytran series was used in cleaving.To adjust a suitable of tension and the entered value of the blade,we can obtain the least damage of the end facet and achieve an effective flat cut-off,which make a good preparation for the later splicing.2.An effective method of splicing between the large-mode-area PCF and the common fiber was demonstrated.A kind of fiber with 250 ?m diameter produced by Nufern was spliced to the large-mode-area PCF by using the splicer of Vytran series.To adjust the power,duration and the heating times,the best splicing effect can be achieved.70% of the signal light can be coupled into the core of the large-mode-area PCF if the bridging fiber is used to mitigate the mismatch of mode area.3.The handling of the output end of the large-mode-area PCF in high power fiber laser was demonstrated.The method of cleaving after collapsing,and using endcap can both obtain a high quality of angle cleaved end facet,which can mitigate the parasitic reflection in the laser cavity.The research is helpful to avoid the continuous lasing because of the parasitic reflection at the end of the fiber in the ultrafast fiber laser.4.A novel multi-wavelength erbium-doped fiber laser based on random distributed feedback(RDFB)has been demonstrated in this thesis due to the drawbacks of high threshold and complicated structure in most of the multi-wavelength fiber lasers based on RDFB.The number of channels can be modulated from 2 to 8 at room temperature when the pump power is changed from 30 to 180 mW,indicating that wavelength competition caused by homogenous gain broadening of erbium-doped fiber is significantly suppressed.The threshold pump power can be as low as 28.6 mW.