Recent progress on S-band fiber amplifiers

The internet boom in the 1990´s led to an exponential increase of the bandwidth demands on optical long-haul transmission links and the introduction of WDM and DWDM systems. However, the gain bandwidth of usual fiber amplifiers is limited to a maximum of 80 nm in the C- and L-band. Todays optical senders and receivers are limited to a spectral efficiency of not more than 1 bit/s/Hz which results in a total capacity of about 10 Tbit/s in the C- and L-bands. Meanwhile the crash of the telecom market damped the bandwidth growth somewhat, but it is still an important task to work on solutions for transmission systems at extremely high bitrates beyond 10 Tbit/s. One of these solutions is the use of larger parts of the low attenuation window of the transmission fibers. It seems to be consensus that the first step towards this direction will be the S- and S⁺-band at 1450-1530 nm. Here we will give an overview of the current status and new developments in the field of S-band fiber amplifier technologies. As usual, the term S-band will be used for Sand S⁺-band in this work.