# Optical Amplifiers for Access and Passive Optical Networks: A Tutorial
## 3 Optical Amplifiers in Telecommunications Networks
### Amplifiers for PONs
Early proof-of-concept experiments have been performed using an optical amplifier at an intermediate powered location in combination with the FEC, which can envisage a 10 Gb/s PON with a split ratio of 1024 [77]. Other PON systems use the C-band, for example, coarse WDM (CWDM) wavelengths of 1530 nm and 1550 nm between the OLT and ONUs). If EDFAs are used as power boosters and preamplifiers, the maximum budget increase is reported to be 34 dB [31]. EDFAs are used for the area of 1550 nm, where video overlay signals are transmitted. In [78], SOAs with Raman amplification are demonstrated for maximum speeds of 2.5 Gb/s. Raman pumping at 1270 nm is used, with a maximum pumping power of 1 W. The results for extending the reach for rural areas are promising, but 1 W is Class IV, and serious eye safety hazards must be carefully considered. British Telecom has demonstrated its long-reach PON. The system used EDFAs and SOAs. With the appropriate optical technologies, 10 Gb/s transmission was achieved in the downstream and upstream channels across 100 km to 1024 customers using a low-cost optical transceiver in the ONU situated in the customer premises [79]. The ACTS-PLANET realized the SuperPON in 2000. The implemented system supports a total of 2048 ONUs and achieves a span of 100 km. The 100 km fiber span consists of a maximum feeder length of 90 km and an add and drop section of 10 km. EDFAs and SOAs were also used [79]. The Photonic System Group of University College Cork in Ireland has demonstrated the wavelength and time-division multiplexing long-reach PON (WDM-TDM LR-PON). The network supports multiple wavelengths, and each wavelength pair can support a PON segment with a long distance (100 km) and a large split ratio (1:256). The LR-PON contains 17 PON segments, each of which supports symmetric 10 Gb/s upstream and downstream channels over a 100 km distance. The system can serve a large number of end-users: 17 \(\times\) 256 = 4352 users [80]. The authors in [81] cooperated with British Telecom, Alcatel and Siemens, who introduced the second-stage prototype of a photonic integrated extended metro and access network (PIEMAN) sponsored by Information Society Technologies (IST). PIEMAN consists of a 100 km transmission range with 32 DWDM channels, each of which operates at symmetric 10 Gb/s and 32 PON segments. The split ratio for each PON segment is 1:512; thus, the maximum number of supported users is 32 \(\times\) 512 = 16384 end-users. Other long-reach topologies considered by researchers include ring-spur topologies for the long-reach PON. Each PON segment and OLT are connected by a fiber ring, and each PON segment can exploit a traditional fiber to the x (FTTx) network with a topology that consists of several \"spurs\" served from the \"ring\". The ring can cover a maximum metro area of 100 km. The natural advantage of the ring topology is two-way transmission and failure protection [79]. An example of this topology was demonstrated by ETRI, a Korean government-funded research institute, which has developed a hybrid LR-PON named WE-PON (WDM-E-PON). In the WE-PON, 16 wavelengths are transmitted on the ring and can be added and dropped to local PON segments via the remote node (RN) on the ring. The RN can include an optical add-drop multiplexer (OADM) and an optical amplifier. The split ratio of the PON segments is 1:32, and the system can support 512 end-users [82]. Another demonstration of ring-based technology, which is called scalable advanced ring dense access network architecture (SARDANA), also implements \"ring-and-spur\" technology. In this system, 32 wavelengths are transmitted on the ring, with a split ratio of 1:32 for each wavelength. More than 1000 end-users are supported. The ONU units are based on a reconfigurable semiconductor optical amplifier (RSOA) [83]. The comparison of LR-PON projects is depicted in Table 3.  
Many tests of different optical amplifiers in the PONs were conducted.