Current laser com systems are getting multiple bits per photon - it seems that the communications field will keep pushing the limits until there is simply no business case, and then push some more. Really, the only limit is Shannon's limit, but that's only concerned with data rate. The modulation schemes that sit on top of the raw data is where all the capacity magic happens.
I assume you're referring to something like this: https://www.sciencedaily.com/releases/2017/02/170203102740.h... but this isn't a scalable transmission system since it's based on single photon detection, and single-photon detection is not a high bandwidth communications ability because you have to discriminate the photons. It's a far cry from "current laser communications".
> the only limit is Shannon's limit, but that's only concerned with data rate.
But that limit, the capacity, is also the maximum possible limit of information transfer on the channel. Modulation schemes don't increase it or change it, they just push the achievable information rate of the system closer to the capacity.
Modulation is definitely the wrong word in this context. I was thinking about channel coding and compression algorithms that increase the efficiency of the system without requiring additional capacity.
