Photonic bandgap fibres are not used in submarine cables their loses are too high. There are recent antiresonant fibres (NANF) which can achieve lower losses th

Photonic bandgap fibres are not used in submarine cables their loses are too high. There are recent antiresonant fibres (NANF) which can achieve lower losses than even SMF. However production capabilities are not ready yet to make the amount of fibre necessary for submarine. The startup (out of Southampton) that pioneered these was recently acquired by Microsoft. We probably see these fibres for links between the exchange and data centres first (although there it is difficult to beat RF links, as they are direct line of sight)