Copper allows creating a movement of electrons, which is what you usually call electricity. Any kind of light, while it allows transferring a signal, does need to have the signal transformed from electricity to light on one end, and from light to electricity on the other.

Replacing a very long cable with a fiber that allows transferring the same signal using light is a way to save on copper. But in appliances themselves, having signals transformed to and from light is too expensive. So you won't find lots of light fibers inside of appliances.