net switch, all in the same chip. The importance of the ONU would be even more evident if we were to make a similar plot for XG-PON1 and XWDM-PON. Here, the challenge of reducing, essentially to a com- modity, a Gbit/s interface supporting a system power budget of about 30 dBm, is really formidable. Another key point in the case of XG-PON1 is the realization of a suitable burst mode receiver both for the ONU and the OLT problem that is an example of the more general problem of the 10 Gbit/s electronics for the access receivers. From this brief discussion, it is evident that optical interface technology is a key to the deployment of next generation access networks, and we will be devoting an important part of the discussion to these components. 11.5.1 GPON Optical Interfaces 11.5.1.1 GPON Interfaces Technology GPON optical interfaces take the name of diplexers or triplexers when analog TV overlay is used. The New Access Network Systems and Enabling Technologies Monitor PIN Laser Splitter driver Laser Digital PIN Analog Fiber coupling section Demux RF PIN Matching network FIGURE 11.13 Functional block scheme of a triplexer for a GPON. A triplexer has one or more WDM filters dividing the three GPON wavelengths (1310, 1490, and 1550) and one laser at 1310 nm, one digital receiver at 1490nm, and one analog receiver at 1550 nm. In a case of a diplexer, a simpler filter is needed, without the 1490 out- put, and the analog TV receiver is not needed either. It is also possible to integrate in the module, the transimpedance amplifier (TIA, see the IM-DD receiver structure in Chapter 6) for the digital receivers to achieve the highest sensitivity. Front-end electronics for the analog receiver is usually located outside the optical assem- bly, due to its thermal dissipation and dimensions. The laser driver for burst-mode opera- tion is also located on an external electronic board. The dimensions of the module can be very different with depending on to the adopted technology. A triplexer block scheme is shown in Figure 11.13.