  We present an exact analytic expression for the Hong-Ou-Mandel (HOM) curve
for any number of identical Micro-Ring Resonators (MRRs) in a linear chain. We
investigate the extreme stability of this HOM curve, showing that the HOM
effect in linear arrays of MRRs is highly robust. We further use this
expression to derive three figures of merit for the HOM curve of linear chains
of MRRs: the minimum tau value ($\tau_{c}$), the curvature ($\bar{\xi}_N$), and
the $5\%$ tolerance in tau ($\delta\tau_{N}$). We promote these metrics to
characterize the pros and cons of various linear chains of MRRs and inform
design and fabrication.
