Devices for that we've been able to make very small. We're very excited about those. For instance, these ring resonators, if you have a stack of these to pick off different channels, you characterize the channel by the diameter of the ring, so it has to be under very tight control. So we need ways of doing trimming and tuning of these things to get them to operate just right, and that's all dimensional control. For the waveguides, when you go to high dielectric contrast in order to shrink things down, the penalty you pay is a greater tendency to light scattering.
Light scatters off any perturbation on the surface of the waveguide.
It acts more as a grating to couple light to the outside. So smoothing is very important. We've been very successful in smoothing the top and the bottom either by CMP or by special depositions, and most recently we've been successful in smoothing the sidewalls by some processes that are very akin to standard processes one would use in IC manufacturing. I see that there are issues, but they are not necessarily issues we haven't faced before and that we can't solve. Probably the biggest issue is process integration.