Rx fiber Drivers and controls PIC-TX Tx fiber FIGURE 11.17 Structure of a transceiver based on PICs. The New Access Network Systems and Enabling Technologies a receiving PIC is identical, with a demux, a bar of photodiodes, and with the WDM signal incoming from the input fiber. Similarly to CWDM SFP, it seems possible to implement CWDM PIC without thermal stabilization. Besides reducing the cost of OLT colored sources, PIC technology can be used also to design colorless ONUs. In this case, a PIC can be used like a tunable source, switching on only the lasers tuned on the desired wavelength. Since PIC technology is still under development, especially CWDM PIC that the market expects to be uncooled, it is difficult to foresee exactly what the cost of one PIC for a certain production volume will be. In any case, considering a 16 wavelength CWDM-PON, in order to have an industrial cost equal to that of a GPON, a 16 elements PIC should cost as much as the unique burst mode interface of the GPON, and this is really very difficult cost wise. The PIC is also the approach to try to reduce interface costs in XWDM-PON. It is to underline that the first PIC prototypes were realized at 10 Gbit/s either for application in the digital optical network or simply to reduce the cost of metro equipment. Also, in the case of WDM-PON, the adoption of PICs have to be taken into account when managing the network. The problem, as in the case of the DON, is OLT PIC failure. In this case, a set of ONUs, if not a complete WDM-PON, loses the signal. Individual protection of PICs into the OLT is thus practically mandatory, and this also impacts on the final OLT cost. As far as the XG-PON is concerned, the discussion is more complex. From the point of view of optical interfaces, on the ground of standard requirements, there are not SO many choices from among the state of the art. The characteristics of the transmitter and receiver are summarized in Table 11.4 for class 1 XG-PON1 (28 dB power budget) and class 2 XG-PON1 (31 dB power span). Thes