1.3-μm Optical Amplifiers

Interest has been increasing in high-speed metro loop optical links of over 10 Gb/s, not only for long-haul transmission systems, but also for medium-span systems based on 1.3-μm zero dispersion fiber. The transmission distance at 1.3 um with a conventional fiber has been limited by the lack of optical amplifiers. There are now three 1.3-μm optical amplifiers to choose from: the praseodymium-doped fiber amplifier (PDFA), the semiconductor optical amplifier (SOA) and the Raman amplifier. PDF As have been used in digital (10 Gb/s) and analog transmission experiments, both in the laboratory and in field trials. The amplification medium of PDFAs is fluoride fiber which has much less chemical durability than silica fiber. This meant that their long term reliability was of serious concern. The question has been resolved recently and it has been shown that fluoride fiber can have a mechanical lifetime of more than 25 years even at high temperature and high humidity (80 C and 80% RH). Another problem has been to improve the quantum efficiency of the 1.3-μm transition of praseodymium. This has now been achieved by using hosts with lower energy phonons, such as indium fluoride-based fibers. There is now the prospect of realizing PDFAs with a lower power consumption for 1.3-um systems and no serious technical problems remain to be overcome.