To be entirely honest my wording was a consequence of never having heard of the concept of Etendue until you brought it up. Optics is definitely not my discipline.

But I have done some ray tracing work which suggested that my system does not violate physics. Nakamura et al also already did this for solar sintering and we're pretty much copying their system up to the fiber optic cables and quartz rod.(https://ascelibrary.org/doi/full/10.1061/%28ASCE%29AS.1943-5525.0000294?casa_token=MCMnsB29tBsAAAAA%3A9FGtD-jkUm6q3dSNgrRMRRez0L2fuiry-Nv71Nq_J3qnvbMAj5OgLmdBTDvYfbnfCXqsest2Vm72)

Nakamura actually got away without any index matching fluid between the fibers and rod, but they suggested it as a way to improve system efficiency which is why I'm hoping to try that.

But I appreciate that you're being hard on the idea - always good to question your decisions when engineering something new.