CW AND Q-SWITCHED NEODYMIUM: YTTRIUM, ALUMINUM, GARNET FIBER LASERS

Research in the field of fiber optics has resulted in the development of a variety of navigation, sensing, and signal processing systems as well as the more widely known fiber optic communication systems. One of the many attractive features of the fiber implementation of such systems is the potentially small size and rugged construction that may be achieved. Many passive optical components such as polarizers and directional couplers have been developed along with these systems.; Active fiber components have also received increasing attention in the last few years. This area has become important since it is desirable to perform functions such as amplification and frequency (or phase) shifting within an optical fiber in order to maintain the all-fiber approach. This reduces loss and promotes miniaturization and stability in these optical systems. Miniature sources are an important part of this development.; Due to the inherent geometrical compatibility with standard silica single mode fiber optic systems high coupling efficiencies can be expected between a fiber laser source and a single mode fiber. This prediction has been verified experimentally under this program. Also, since this type of laser may be made of a solid-state material such as Nd:YAG greater frequency stability may be obtained compared to a laser diode source. Another advantage of a fiber laser is that its inherently small size allows it to run without the need for a cooling system.; The work reported here represents continued development of fiber laser sources. Fiber lasers made of Nd:YAG were evaluated experimentally in a cw mode of operation at a signal wavelength of 1.319 (mu)m. Dye laser pumping at (lamda)(,p) = 0.808 (mu)m was implemented for the first time as a prelude to laser diode pumping at this wavelength. These same lasers were also operated at a wavelength of 1.064 (mu)m in order to gain some insight into the nature of the loss in fiber lasers. Low device thresholds and high pump/signal conversion efficiencies were demonstrated at both signal wavelengths. Some of these fiber lasers were surrounded by a high index cladding layer for the first time which tended to reduce the loss per unit length in the fiber.; Q-switched laser action was also demonstrated and characterized for the first time in fiber lasers using both mechanical and passive methods.; Theoretical models, developed under this program for both cw and Q-switched fiber lasers, indicate that they can have much lower thresholds than their conventional counterparts because of the guided-wave nature of the interaction between the pump and signal fields in this type of device. These models have also been used to study the effect of fiber parameters upon laser performance which is necessary for the design of optimized fiber lasers.; Single crystal fibers made of Nd:YAG combine the advantages of a fiber geometry with the high gain per unit length of this excellent solid state laser material and may soon prove to be very useful devices in the fields of fiber optics and optical communication.