The topic of this thesis is solar pump Nd-doped double-clad fiber laser, the main characteristic of this research is we use nature and low pollution source pump unique laser gain medium. By using Neodymium-doped double-clad fiber in form of waveguide structure to replace Neodymium-doped glass, Neodymium-doped yttrium aluminum garnet crystals that have large cross-section area of the volume in the past¡F natural sunlight is used as pumped source in instead of diode laser, pulsed Xenon lamp, Krypton arc lamp¡Ketc. In order to reduce the use of electric power source and decrease the pollution . By using Solar concentration system, we focus average sunlight power density (800W/m2) to very high power density. In application, If lasers are needed in remote locations where sunlight is abundant and other forms of energy sources are scarce, this kind of solar energy usage is not a bad idea.

Rapid development of fiber-optic communications network requirements increasing in recent years, The WDM technology and invention of anhydrous optical fiber open the possibility for optical fiber transmission bands broaden form 1.3 £gm to 1.6 £gm. Chromium doped yttrium aluminum garnet crystal fiber has characteristic of 300 nm broadband. Therefore, it¡¦s strongly desirable to develop a broadband fiber amplifier, laser or other active components for extending the flexibility of system architecture design in optical fiber communication. A few-mode chromium doped yttrium aluminum garnet double-clad crystalline fibers has been demonstrated by employing a modified version of LHPG technique, means using silica-YAG crystal co-drawing and multiple core-tuning process by precisely controlled inter-diffusion between YAG core and silica tube. In this thesis, electron probe x-ray micro-analysis, energy dispersive spectroscopy and transmission electron microscopy were utilized to confirm this fiber structure and composition. This fiber has gross gain about 2.3 dB with dual pumped by few hundred mini Watt. Significantly reduce the pump power threshold. Compared with the last large core size, few-mode (small core size) chromium doped yttrium aluminum garnet double-clad crystalline fibers has lower heat effect and higher power efficiency. To enhance the optical properties towards few modes or even single mode, not only reduce the transmission loss, but improve the device efficiency. Key words: Laser heated pedestal growth, Cr4+:YAG, Double-clad Crystal Fiber, gain

During last decade, the fast-growing communication need has promoted the development of 1.3 £gm~1.6 £gm laser light source. The Cr4+ doped YAG solid-state laser has potential to meet this broadband demand. In addition, diode-laser-pumped solid state laser has the merits of high laser beam quality, long lifetime, compact, and simple structure. In this thesis, crystal fiber was used as the laser gain medium, and coated with optical thin film at its end facets as the laser cavity. Using this configuration, the volume and cost of the laser can be appreciatively reduced, and the heat dissipation can be improved. The laser-heated-pedestal-growth method was used to grow crystal fiber, which can obtain small diameter at very fast rate. Outside the glass clad Cr4+:YAG crystal fiber, Al-Cu alloy was employed as the heat sink to improve heat dissipation. After grinding, polishing, and coating of this device, the Cr4+:YAG crystal fiber laser was fabricated. Some characteristics of Cr4+:YAG crystal fiber, such as the distribution of Cr2O3 and CaO doping concentration, fluorescence intensity, refraction index, propagation loss, and absorption coefficient were measured and analyzed. A record-low threshold of 0.75 mW was achieved. It is more than 500 times lower than any previously reported Cr4+:YAG lasers, and a slope efficiency of 6.9% was obtained. The ultralow-threshold lasing is made possible by the low propagation loss of 0.08 dB/cm and the high pump intensity of the core. Such a low-threshold operation makes the double-clad crystal fiber laser be compatible to present optical communication systems. In the meanwhile, some simulations of the laser output power have been developed to predict the experimental results.