Study Of Design, Fabrication And Characteristics Of Photonic Crystal Fibers With Large Mode Area

Because Lasers in the rang of3~20 m have important applications and prospect in infrared spectroscopy, remotesensing, medical, environmental protection, laser cutting, radar and weapons, and many other areas, high power fiber lasersand amplifiers in this spectral rang have become the research focus at home and abroad. In order to overcome the nonlineareffect and thermal damage caused by high power density, and to conquer the limitt of transmission wavelength below2min quartz, Chalcogenide photonic crystal fibers with large mode area will be a good device for infrared high power fiberlasers and amplifiers. And then extensive attention is paid to the design, fabrication and properties of chalcogenide photoniccrystal fibers with large mode area.In this paper, chalcogenide photonic crystal fibers with large mode area are studied in theory design and experimentalfabrication. In theory, the implementation methods of photonic crystal fiber with large mode field are mainly studied. Twokinds of photonic crystal fibers which have large mode field area are designed by using multipole method and beampropagation method. In experiment, the optical and thermal properties of chalcogenide glasses as well as mechanical propertyare carefully studied, a chalcogenide glass of Ge20Sb15S65is thought as a good matrix material for photonic crystal fibers.More importantly, how to fabricate fiber preforms based with chalcogenide glass and how to make photonic crystal fiberswith perfect structure are studied.At last, a series of photonic crystal fibers wtith different structures are obtained and aretested with optical platform we construct by ourselves. It turns out that the fibers we made own the properties of large modearea of2000m2and low lossof about2-3dB/m.In chapter1, a brief overview of the characteristics of the photonic crystal fibers, as well as their transmissionmechanism is given; The characteristics of chalcogenide glass, research progress of photonic crystal fibers with large modearea, implementation methods and their applications are introduced. Finally, the purpose and content of this study has beenexpressed.In chapter2, numerical simulation methods of multipole method and beam propagation method, which are used in ourdesigns, are intruduced, and some simple derivations are performed.In chapter3, a design thinking of single mode photonic crystal fiber with large mode area which will be used in infraredapplications is put forward. A photonic crystal fiber based on a arsenic-free environmentally friendly chalcogenide glass ofGe20Sb15Se65is proposed,which works with large mode area and single mode. At wavelength of10.6m, the fiber workswith utra-large mode area of13333m2, as well as small confinement loss for the fundamental mode, lower than0.1dB/m,high confinement loss exceeding2dB/m for the higher-order mode.In chapter4, a closed-packed seven-core PCF based on the environmental non-arsenic chalcogenide glass ofGe20Sb15S65is designed. Phase locking and mode shaping in multicore Ge20Sb15S65chalcogenide photonic crystal fibersare proposed and demonstrated. By manipulating the geometrical structure of the fibers, a large mode area of1962μm2resulting from in-phase supermodes and equal amplitudes was obtained, which can significantly reduce the nonlinear damagein chalcogenide fibers in the infrared spectrum. With the coherent beam combining technology of multicore photonic crystalfibers, the far-field combining beam exhibits high brightness and high beam quality. Calculations show that with good phaselocking and mode shaping, a seven-core photonic crystal fiber can achieve49times enhanced intensity compared withsingle-core fibers, as well as Mx2=1.350，My2=1.295.In chapter5,the preparation process and testing method of chalcogenide glass are introduced in detail, properties ofchalcogenide glass Ge20Sb15S65are also studied.In chapter6, a preparation technology of mechanical drilling method for fabricating chalcogenide phtotonic crystalfibers is studied, and a aseries of photonic crystal fiber preforms with different structures were fabricated by this precisemethod.In chapter7, drawing technology of chalcogenide-based photonic crystal fiber is studied in detail. Because the viscosityvalue is not available, PCF preforms are drawn at different temperatures, namely,430℃,435℃, and465℃. After that,X-ray diffraction (XRD) is performed on the drawn PCFs, and confirms that chalcogenide glass of Ge20Sb15S65is a goodcandidate for photonic crystal fiber. A series of photonic crystal fibers with different structures are obtained at430℃, andtheir near field and transmission loss are tested, the loss is about2-3dB/m.Finally, some conclusions of the research are drawn, and the shortages of this research work, as well as something yetto be perfect are also pointed out.