> Any people with knowledge in the field care to comment on whether it's feasible for a light (em?)-type, active, near-range detection system to work?

I’m not in the field, but I follow it enough to say: in theory, yes, (blue-green lidar), and there is a lot of work on moving this from theory to practice.

But approximately everyone is working on it (for bathymetry and for detecting subs, and similar blue-green laser tech for underwater comms), so its likely once its deployed so that a sub could in principle use it as a “headlight”, it’ll raise similar concerns to sonar, because if it is used actively, passive sensors looking for active use will also be common.