There have been some recent advances which greatly improved the optical bandwidth and make such projects much more feasible cost wise: https://www.nature.com/ar

There have been some recent advances which greatly improved the optical bandwidth and make such projects much more feasible cost wise: https://www.nature.com/articles/s41377-023-01201-7 https://www.nature.com/articles/s41377-023-01201-7 Single digit amount of photons is needed per bit.