Recently, with the escalating demands for optical communications, the need for bandwidth in optical communication network has increased. The technology breakthrough indry fiber fabrication opens the possibility for fiber bandwidth form 1.3 to 1.6 £gm. Cr4+:YAG double-clad crystal fiber (DCF) grown by the co-drawing laser-heated pedestal growth method has a strong spontaneous emission spectum form 1.3 to 1.6 £gm. Such fiber is therefore, eminently suitable for optical coherence tomography (OCT), broadband optical amplifier, amplifier spontaneous emission (ASE) light source, and tunable solid-state laser applications. In this thesis, multilayer dielectric thin films were directly deposited by E-gun coating onto the end faces of the Cr4+:YAG DCF. To improve the thin-film quality, to increase transmittance of laser output, and to design for the high power laser. For broadband optical amplifier in dual-pump and double-pass scheme, a 3.0-dB gross gain, a 3.0-dB insertion loss, and a 0-dB net gain at 1.4-£gm signal wavelength have been successfully developed with HR coating onto one of the Cr4+:YAG DCF end faces. In addition, we have successfully developed the Cr4+:YAG DCF laser by direct HR coatings onto fiber end faces and increase transmittance of laser output. A record-low threshold of 31.2 mW with a slope efficiency of 7.5% was achieved at room temperature.