Drol

The problem with photonic chips is that the devices are enormous in comparison. Something simple like routing the light around a 90 degree corner already takes in the order of a millimeter. Simply scaling down the waveguide causes the light to fly out of the corner, causing reduced signal strength and random scattering through the chip, heating it up. A chip with more than a few hundred devices will probably quite large already and will cause low yield, high cost and high power consumption (it likely requires cooling). I don't see optical chips replacing transistor based chips in my lifetime, except for a few specialized applications (high frequency radio maybe).