Design And Fabrication Of Large-mode-area Single Mode Erbium Doped Irregular Bragg Fibers And Related Devices

Rare-earth-doped large-mode-area single-mode fibers and related devices are critical parts for high power fiber lasers and amplifiers, and have great applications in fiber communication, sensing, manufacturing, surgery, and military, etc. Under the supports of national 863 high technology program and national nature science foundation, this thesis is devoted to fabrication of large-mode-area Erbium doped irregular Bragg fibers and related devices. The main achievements of this thesis are listed as follows:1. A novel irregular Bragg fiber, which has alternating layers of high and low refractive indices that can provide significantly larger mode area than common fibers under the same refractive index levels, is proposed to fabricate large-mode-area Erbium doped fibers by using the solution doping technique and MCVD method with necessary improvements. The fabrication difficulty in equipments, technique, and control are greatly decreased. Irregular Bragg fiber with different design can meet different requirements. Under the guidelines for fiber design based on theoretical analysis on irregular Bragg fibers, ordinary Erbium doped large-mode-area single-mode fibers with irregular Bragg structure are fabricated. The effects of different dopants to the edge of layers are discussed, the method of keeping clear edge are proposed and applied in fiber fabrication, and achieve good result.2. The rare-earth doped processing based on novel fluorine doped porous layers that can keep the index in a low level as well as high rare-earth consentration are first proposed and realized. One-layer-core fiber fabricatede by using this processing has rather high absorption coefficient of 100dB/m at 1530nm. By using this, the single mode irregular Bragg fiber fabricated has a significantly larger core area, and presents superior characteristic on rare-earth absorption.3. Double clad irregular Bragg fibers with large air-hole outer clad are fabricated by using special pressure control processing to increase numerical aperture. This structure is easy-fabricated and of high fabrication error tolerance.4. A novel beam-shaping method for laser diode array using confocal parabolic mirror are first proposed and tested. For parallel beam-shaping, this method significantly decrease the beam length, as well as maintain it's divergence angle. 5. The feasibility of writing gratings on photosensitive rare-earth-doped large-mode-area single-mode irregular Bragg fibers to form fiber devices is been proved both theoretically and experimentally. Experiments also indicate that irregular Bragg fibers are able to show good photosensitivity after H2-load and well satisfy the requirements of fabricating devices. Annealing has little effect on grating characteristic and absorption coefficient of Er3+in fiber.