As a reference to existing problems with silicon photonics I am including some detail from one of my lasts posts re Dr Lucas Soldano

Perhaps the most significant issue with silicon photonics is that silicon as a material, unlike Indium Phosphide, does not possess a direct bandgap. By that we mean that electrons and holes of the lowest energy have different momentum states, and therefore cannot combine directly to generate light. In a forward biased silicon pn junction, the carriers recombine non-radiatively and thus one cannot make LEDs or lasers in silicon. Generally there have been three workarounds for this problem. The first is obviously to have the light off the chip, so a separate indium phosphide laser generates the light and the light is then coupled to the silicon chip where it is modulated and then sent out. The challenge here is of course the complexity of getting the light on and off the silicon chip, especially if multiple wavelengths or multiple sources of light are needed. The second more ambitious way is to try to incorporate the direct gap indium phosphide material on the silicon. The different lattice constant, chemistry, and processing requirements of the indium phosphide make it difficult to fabricate efficient lasers this way. Furthermore, it is impossible to test or burn-in the laser prior to assembly and the relatively poor yield of the lasers increases the cost of the entire assembly. Perhaps the ultimate solution is to try to make the silicon direct gap by adding impurities or changing the crystal through physical deformation. Needless to say, this is very challenging.