Due to the fast expansion and development in the optical communication industry, the demand for the broad-band laser light source as used to the optical transmission network system has correspondingly increased. Cr4+ doped YAG crystal fibers, with its broad-band spectral property, is thus becoming more and more indispensable to the growth of the industry. However, the Cr4+:YAG crystal fiber in its own repetitive growth process brings with itself one problem: after each re-growth, the concentration of Cr2O3 and Cr4+ ions would reduce appreciatively. Hence, finding sound solutions for effectively raising the concentration of Cr4+ is now becoming an essential issue in the field. The thesis mainly focuses on the development of using Cr4+:YAG as the laser gain medium. Thin layers of CaO, MgO, and Cr2O3 was coated on the circumference of the Cr:YAG crystal fiber. The LHPG method was then employed to re-grow the coated samples, during which the doped concentration of CaO, MgO and Cr2O3 can in-diffuse. And the effect of charge compensation would go further to simultaneously raise the concentration of Cr4+ ions. Now we have successfully enhance the concentration of Cr4+ ions to 4.86x10-3 wt.%. This study, with the use of the E-Gun coating machine and the IAD (ion-beam assisted deposition) system, also probes the technical side of how to better improve the quality of the crystal fiber laser. Both end faces of the Cr4+:YAG crystal fiber were coated with optical thin films by TiO2 and SiO2 targets. In addition to raise the quality of the thin films, the IAD system also functions to create a laser cavity in which both the anti-reflectance (AR) effect (for pumping the light source) and the high reflectance (HR) effect (for stimulating the light source) are achieved. The accompanied benefits would be the reduction of transmission loss, the increased laser efficiency, and thus a more successful and more stable crystal fiber laser.