Yeah I was going to say... They've done something which is cool, but really we already knew it was possible, and is not the hard bit of optical computing.
Essentially they made a fancy prism. We need an optical transistor.
It's very difficult to get photons to strongly interact with each other. An optical transistor would revolutionize both classical optical computing and quantum computing.
There are optical switches around. They work by making the material transparent or not depending on an impulse.
The problem is that they are big, slow, monochromatic, hard to build and actually consume more energy than transistors to operate. That's why a breakthrough on that would be interesting.
Essentially they made a fancy prism. We need an optical transistor.