Comment by dawnofdusk

>what this routing mechanism is (heating a substrate, maybe?)

You can engineer a waveguide if you understand the nonlinear theory they propose. There's no heat exchange involved, which is easy to get confused on because the writing in the article does not really understand "optical thermodynamics".

>if the routing is dynamically changeable

At this point probably not, it requires a finely engineered waveguide which has a well-defined "ground state"

>it works in reverse, eg light coming in can be routed to one of several output ports

In theory it works in reverse, as everything in this system is time-reversible (i.e., the "optical thermodynamics" is just an analogy and not real thermodynamics, which would break time reversibility). This is demonstrated via a simulation in the SI, but experimentally they did not achieve this (it may be difficult, I am not an experimentalist so cannot comment).