Studies On Fabrication Of Integrated Double-Clad Photonic Crystal Fiber Amplifier

As a key component in all-fiber laser,the tapered fused-bundle pump-signal combiner has been widely used in the master oscillation power amplifier(MOPA)structure of all-fiber high power laser system.Double-clad photonic crystal fiber(DC-PCF)has been widely used in fiber laser system because of its excellent properties like large mode field area,high clad numerical aperture,and endless single mode.While,the air-hole structure makes DC-PCF difficulty to cleave and splice.Therefore,the reported fiber amplifier based on DC-PCF is almost free-space structure,which is less stable and reliable than all-fiber structure.Based on all above,we study and fabricate an integrated double-clad photonic crystal fiber amplifier,which uses an Yb-doped double-clad photonic crystal fiber as output fiber of pump-signal combiner.This integrated amplifier can not only make full use of excellent property of DC-PCF but also realize its all-fiber structure use.In this way,DC-PCF can be more widely used in fiber laser and amplifier system.The main work of this thesis is listed as below:1.Based on the Mode-Field Diameter(MFD)Method,we deduce the equations of coupling efficiency for fibers under different splicing conditions.We also use these equations to analyze coupling efficiency between signal and output fiber in fiber combiners,which are fabricated by tapered fiber bundle(TFB)technique.The mode-field mismatch loss is mainly concerned.The calculated result is close to the coupling efficiency of basic mode calculated by Beam Prop Method.2.We study and learn the fabrication process of making pump-signal fiber combiner using a capillary tube.First of all,we solve the problem of making sure signal fiber and pump fibers in the right position of tube,namely signal fiber in the center of TFB and pump fibers around it.We also learn how to make a high quality cleave of TFB and perfect splicing with output fiber.These fabrication technology is the base for making pump-signal fiber combiner.3.We fabricate(6+1)×1 pump-signal combiner with SMF-28 as signal fiber and 25/250?m double clad fiber as output fiber using a capillary tube.Mode-field adaptor for signal fiber is based on thermally expanded core(TEC)technique.Theoretically,we study the effect of different heating time on signal coupling efficiency.Then,we use the optimal heating time of 30 minutes to fabricate TEC fiber.The signal coupling efficiency improves from 52% to 93%.4.Based on the mode field analysis by Finite Element Method(FEM),we calculate the signal coupling efficiency when the air-hole width of photonic crystal fiber(PCF)changes.It comes out that the air-hole should collapse as little as possible when we splice TFB to PCF.In the experiment,based on fabrication technology of making fiber combiners,we successfully splice the TFB to double clad polarization photonic crystal fiber and fabricate an integrated DC-PCF amplifier,which uses PM-10/125?m fiber as signal fiber.By changing the splice parameters,the coupling efficiency of integrated amplifier for continuous seed light improves from 69% to 89%.