Extending reach of passive optical networks through optical amplification

In this paper, the research progress on increasing the reach of passive optical networks (PONs) by means of optical amplification is reported. The work is focused on next generation PON operating at 10 Gb/s with long reach up to 100 km and high split. The studied amplifier is the erbium-doped amplifier operating in the C-band. It is a mature technology largely used in the metro and long-haul network due to its relative flat and broad gain. In order to handle the bursty upstream traffic and overcome the different signal power level due to different distance between several optical network units (ONUs) to optical line terminal (OLT), a gain clamping technique to stabilise the amplifier is investigated. A dual-stage amplifier is used to obtain high gain at large input power excursion. The optically clamped amplifier provides gain over 22 dB up to a total input power of -3 dBm. The gain excursion is less than 1.6 dB for a large input power variation. Overall the experimental results show that the optical feedback loop is a simple and cost effective technique to guarantee amplifier robustness for typical upstream PON traffic.