Things have changed since you have been diving. Not about the toxicity of O2 at depth (I think at pressures above 2 atmosphere (below 10m)) but the use of pure Ox in diving.

These days there are mixed gas rebreathers. They work by mixing the breathing gas in the system in real time,and removing the co2 fully self contained. So diving with no bubbles. They use high pressure pure Ox to feed the system. Often 3 or 4k psi in small spherical tanks. As you can imagine this is not cheap, and quite technical. Google Mixed Gas Rebreathers if interested.