Semiconductor Optical Amplifiers for FTTx

Abstract

Access networking is a hot topic. After Japan and Korea, demand is now picking up also in Europe and the US. After cherry-picking the easy installs, operators find that they could use a power boost in their passive optical networks to reach further out neighbourhoods from their present set of PON central offices. Hence the push for introducing optical amplification in access. As always, the main aim is cost reduction. Fewer COs means lower opex, while amplification before the PON splitter may mean higher split ratios, which in turn means that the same central office equipment can serve more end customers. Given the wavelength plan of a typical PON, the choice of optical amplifiers is limited to SOAs or Raman-assisted SOAs, depending on whether gain-flattened operation in a CWDM-PON is desired. Possible locations of the amplifier are as a booster/preamp at the OLT, or as a line amplifier near the passive splitter. These set different output power / noise figure requirements, where the in-line configuration allows for longer distances between the CO and the end customer, and/or higher split ratios. Operating regimes to be distinguished are NF-limited, gain limited, and power limited. Access networking is a hot topic. After Japan and Korea, demand is now picking up also in Europe and the US. After cherry-picking the easy installs, operators find that they could use a power boost in their passive optical networks to reach further out neighbourhoods from their present set of PON central offices. Hence the push for introducing optical amplification in access. As always, the main aim is cost reduction. Fewer COs means lower opex, while amplification before the PON splitter may mean higher split ratios, which in turn means that the same central office equipment can serve more end customers. Given the wavelength plan of a typical PON, the choice of optical amplifiers is limited to SOAs or Raman-assisted SOAs, depending on whether gain-flattened operation in a CWDM-PON is desired. Possible locations of the amplifier are as a booster/preamp at the OLT, or as a line amplifier near the passive splitter. These set different output power / noise figure requirements, where the in-line configuration allows for longer distances between the CO and the end customer, and/or higher split ratios. Operating regimes to be distinguished are NF-limited, gain limited, and power limited.