  The group-theoretic content of photonic coupled microrings resonance
phenomena is shown, in particular, an interesting emergence of pseudo-unitary
group. The application to the resonance condition in a tri-microring
configuration is solved exactly. A practical application of this work will be
in the resonance frequency tuning based on the coupling coefficient, in
particular, the Mach-Zehnder interferometer approach was analyzed for the
coupling modulation.
