  We introduce a theoretical framework for the rational approximation of
optical response functions in resonant photonic systems. The framework is based
on the AAA algorithm and further allows to solve the underlying nonlinear
eigenproblems and to efficiently model sensitivities. An adaptive sampling
strategy exploits the predominance of resonances in the physical response. We
investigate a chiral metasurface and show that the chiroptical response on
parameter variations can be accurately modeled in the vicinity of the relevant
resonance frequencies.
