ABSTRACT
The recent interest in optical amplifiers and lasers based on rare earth doped fibers has stimulated a new look at fiber fabrication methods. The use of optical fiber to reduce the required pump power for gain in glass lasers and amplifiers was first demonstrated in the early 1960s by Snitzer and co-workers [1, 2]; revisited in the 1970s by Stone and Burrus [3], it has been pursued with vigor since 1985. The rebirth of this field has been stimulated primarily by the application of optical amplifiers and fiber lasers to optical communications. This commercial interest, combined with the availability of high-power semiconductor pump lasers and low-insertion-loss wavelength division multiplexers and isolators, has resulted in rapid development of active fiber devices. The bias toward fiber communications has provided a strong incentive to consider active fiber designs and compositions compatible with standard low-attenuation, silica-based fiber. Specifically, the ability to connect active fiber components to doped silica telecommunications fiber by fusion splicing, with low insertion loss and low reflectivity, allows the interconnection of reliable, low-noise, high-gain amplifiers. This same telecommunication bias has likewise directed rare earth doped fiber fabrication toward variations on traditional doped silica processing. There exists however, in addition to this mainstay, a growing body of work on the less compatible compound and fluoride glass active devices that may overcome the current emphasis on doped silica by offering other operating wavelengths, higher gain, higher-output power, or broaderband operation. It is the function of this chapter to describe the methods developed for fabricating rare earth doped, silica-based fibers, emphasizing how processing affects the physical properties and performance of the resulting fibers. This topic has also been reviewed in earlier papers [4-7].
