Optical Fiber Devices: Novel Fiber Lasers and Image Amplifier

Abstract

Three fiber based optical devices: all phosphate glass fiber laser, single hybrid mode fiber laser, and fiber image amplifier, were investigated in this dissertation. Phosphate fiber Bragg grating (FBG) is desired to improve performance of recently developed high power single frequency lasers that were based on highly rare earth ion doped phosphate fibers because these lasers were fabricated with silica FBGs that have incompatible properties with standard phosphate glasses. Since standard phosphate glasses are not photosensitive, Ge-doped phosphate glasses were fabricated and their UV-photosensitivity was examined. A phosphate fiber that has Ge-doped core showed UV index changes more than ~1.1 × 10⁻³. An all-phosphate fiber laser was also demonstrated with the Ge-doped phosphate FBG. Single hybrid mode fiber laser that involves a large area mode in cavity formation was demonstrated. The fiber laser consists of an Er-doped active fiber and two FBGs. One FBG was a core-cladding mode converter, and the other FBG was a narrowband high reflector that selects the lasing wavelength and mode. This approach for designing a laser cavity provides a much larger mode area than conventional large-mode-area stepindex fibers, and is supposed to suitable for a high power fiber laser. Also this configuration allows us to make novel ring-like cavities and sensor devices that consist of higher mode of optical fibers. Image amplifier based on a highly rare earth ion doped phosphate fiber is a unique approach to overcome weakness of widely used image intensifiers that lose a lot of information in the image, such as spectral distribution, polarization, and phase. Image amplification with a 19-pixel optical image amplifier array based on high gain per unit length Yb³⁺-doped phosphate glass optical fiber was demonstrated. A 10-cm of the 19- pixel fiber image amplifier provides spatially uniform image amplification with gain of 30 dB/pixel or more. This image amplifier responds quickly to changes in the image position – with potential for GHz-level or higher frame rates. This unique approach for image amplification offers low noise, high gain, and wide field of view in a compact fiber-based device.