[peter_retief]

I immediately thought of the old crystal radios and a short search brought up this comparison. While old radios used a natural mineral (galena) to detect radio waves, modern Rydberg radio receivers use a synthetic photonic crystal (often made of silicon or glass) to guide and enhance the radio signal for improved performance.

[jacquesm]

That's not the function of the crystal though, it is not optical but 100% electrical and serves to demodulate the signal, not to receive it.

[peter_retief]

https://www.mpg.de/9142418/magnetism-in-artificial-crystal and this