Pulling bulk crystal into fiber is suitable for laser, amplified spontaneous emission (ASE), and optical amplifier applications in optical communications because of its structural similarity to silica fiber. Moreover, fiber configuration can confine pump light in a small cross-sectional area with a high energy density for a long distance. Among crystal fiber growth techniques, the laser-heated pedestal growth method (LHPG) was adopted. It is crucible free and can therefore produce high-purity, low-defect-density single crystals. However, interface loss of the crystal fiber is one of the main causes of optical loss. In order to reduce the optical loss, a proper method to clad the fiber is important for high device performance. For laser application, high-efficient Nd:YAG lasers were demonstrated using gradient-index crystal fibers. We used controlled profile of the active ion resulted in index difference of 0.0284 between the center and the edge of the fiber to confine the laser beam in the center region and thus reduced the interface loss. A laser output power of 80 mW was achieved with a slope efficiency of 28.9%, which, to our knowledge, is the highest ever achieved for diode-laser-pumped Nd:YAG fiber laser. For ASE and optical amplifier applications, Cr4+:YAG crystal fiber was studied due to its fluorescent spectrum just covering the low loss window of silica optical fiber. To reduce the fiber diameter and propagation loss, a novel cladding technique, codrawing LHPG (CDLHPG), was developed. Although fused-silica-clad fiber can be made with a 29-micron-diameter core and a propagation loss of less than 0.1 dB/cm, which is a factor of 7 smaller than that of an unclad fiber, it has almost no Cr4+ fluorescence in the core area due to the entering of SiO2 in YAG. With proper controlled growth parameters of the CDLHPG method, a double-clad fiber with a core diameter of 25 micron was successfully grown. Up to 2.36 mW of ASE with a bandwidth of 265 nm was demonstrated. After splicing the double-clad fiber with conventional single mode fiber, we successfully demonstrated the first transition metal-doped fiber amplifier in the optical fiber communication band. Up to 16-dB of gross gain at 1.47 micron was achieved.