7. Results and discussion

In this section, we present the obtained simulation results with further discussion on NG-PON2 physical layer architecture design and development based on PICs. Figure 13 shows the spectral simulation results obtained using advanced simulator for photonic integrated circuits (Aspic) software from filarete. On the left figure, there is the downstream operation (L band selected), and on the right there is the upstream (C band selected). In the figure, the spectra in blue, pink, orange, and green are the four channels. In both cases, it is possible to conclude that there is about 30 dB of suppression of replicas. The suppression facilitates smooth operation of the system by preventing intra-channel interference.

The reason for using laser cavities is due to the limitations on the foundry. During the chip's design period, the Smart Photonics did not offer lasers on their process design kit (PDK). Consequently, improvements in the architecture can be undertaken to potentiate the results. For instance, the laser cavities could be replaced by distributed feedback (DFB) or distributed Bragg reflector (DBR) lasers that have narrow linewidth and a stable single mode operation. In this case, the cavity would disappear, and the filtering should be done after the lasing. In addition, the architectures can be simplified using only one modulator; nevertheless, it

Figure 13. Optical spectra at the transmitter output (a) downstream and (b) upstream.

would not be possible to transmit the four channels simultaneously; this implies that only one channel can be transmitted at a time. The proposed and developed architectures demonstrate the potential of photonic integration for optical architectures. Consequently, the architectures not only have the ability of supporting high data rates, high density, and flexible solutions but also offer advantages such as low power consumption, improved functionality, low footprint, and cost-effectiveness.
