The hydroxyl loss increase characteristics for antimony oxide-doped silica fibers were investigated to ensure long-term reliability. The loss increase was measured for non-irradiated and γ-irradiated fibers with hydrogen molecule diffusion and heat treatments. The loss increase characteristics for these experiments were similar to those for germanium oxide-doped silica fibers.

Fundamentals and development of PDFAs are described. Spectroscopic data of Pr3+ in a fluoride glass are presented with a view to understanding the performance of PDFA. An amplification mechanism model which explains PDFA performance is established. On the basis of the model pump schemes which efficiently extract the potential in Pr3+-doped fluoride fiber are discussed in order to construct amplifier modules. Gain characteristics of Pr3+-doped fluoride fibers are clarified. Codoping effect on pump wavelength extension is investigated. LD-pumped PDFA construction and performance are described. PDFAs are shown to be attractive device to upgrade the performance of optical systems at 1.3µm. Furthermore future approaches to PDFA research are discussed.

This letter reports in detail on the temperature-dependent signal gain characteristics of Er3+-doped optical fiber amplifiers at signal wavelengths of 1.536µm and 1.552µm. The amplifiers were pumped at 0.825µm in a temperature range of 40 to 200. The signal gain for optimum length at both wavelengths stops increasing and begins to decrease at about 80. In the temperature region below 80, both signal gains increase with fiber temperature for fibers of optimum length or less. A temperature independent length aroud the optimum length is observed from 80 to 200 for both signal wavelengths. Theoretically, the temperature dependence of the signal gain characteristics rerults from the changes in fluorescence, absorption, GSA and ESA cross sections.

Basic characteristics of Erbium-doped fiber laser amplifier (EDFA) pumped by laser diodes with oscillating wavelength of 1.48µm are measured. Unsaturated gain of 26 dB, 3 dB saturation output power of 1 mW, and noise figure of 5.5 dB are obtained. As a result of transmission experiment using the EDFA at 1.8 Gbit/s over 210 km, linear repeater gain of 20 dB is achieved by considering loss of optical band pass filter and power penalty due to degradation of extinction ratio. By using the basic parameters obtained experimentally, maximum regenerative repeater spacing are calculated in a direct detection transmission system with EDFA repeaters. It is clarified that theoretical regenerative repeater spacing of 5000 km can be achieved by using 50 amplifiers with gain of 20 dB and noise figure of 6 dB, including coupling loss of 0.5 dB, at a bit rate of 2 Gbit/s.