There are... I think they aren't unproblematic - the fibre can get caught on things etc. Also I read of instances where the opposition can follow the fibre back to find the drone operators.
Tracing the fiber back is possible only in extremely favorable conditions. The light must hit the cable just right and there cannot be too many cables from previous runs on the battlefield.
Those cables are 10km long. You can trade a couple hundred meters when the drone is flying by, but there are several KM that you cannot even see at the same time as you can see the drone.
This is why it's so fascinating to read about this conflict. The back and forth innovations (some obvious, some rudimentary, some very much not) is just incredible to follow.
Early on: Drones in war!
Then: Ahh EW makes them useless!
Then: Fiber optics defeat EW!
Then: But you can follow the cable!
Then: But you can try to respool the cable with a power drill!
