  A multitude of large-scale silicon photonic systems based on ring resonators
have been envisioned for applications ranging from biomedical sensing to
quantum computing and machine learning. Yet, due to the lack of a scalable
solution for controlling ring resonators, practical demonstrations have been
limited to systems with only a few rings. Here, we demonstrate that large
systems can be controlled by using only doped waveguide elements inside their
ringswhile preserving their area and cost. We measure the large photoconductive
changes of the waveguides for monitoring the rings' resonance conditions across
high-dynamic ranges and leverage their thermo-optic effects for tuning. This
allows us to control ring resonators without requiring additional components,
complex tuning algorithms, or additional electrical I/Os. We demonstrate
automatic resonance alignment of 31 rings of a 16 x 16 switch and of a 14-ring
coupled resonator optical waveguide, making them the largest, yet most compact,
automatically controlled silicon ring resonator circuits to date, to the best
of our knowledge.
