  The Vernier effect has seen extensive application in optical structures,
serving to augment the free spectral range (FSR). A substantial FSR is vital in
a myriad of applications including multiplexers, enabling a broad, clear band
comparable to the C-band to accommodate a maximum number of channels.
Nevertheless, a large FSR often conflicts with bending loss, as it necessitates
a smaller resonator radius, thus increase the insertion loss in the bending
portion. To facilitate FSR expansion without amplifying bending loss, we
employed cascaded and parallel racetrack resonators and ring resonators of
varying radius that demonstrate the Vernier effect. In this study, we designed,
fabricated, and tested multiple types of racetrack resonators to validate the
Vernier effect and its FSR extension capabilities. Our investigations
substantiate that the Vernier effect, based on cascaded and series-coupled
micro-ring resonator (MRR) sensors, can efficiently mitigate intra-channel
cross-talk at higher data rates. This is achieved by providing larger
input-to-through suppression, thus paving the way for future applications.
