Investigation of cascaded SiN microring resonators at 1.3 µm and 1.5 µm

An optical device operating at wavelengths around 1.3 µm and 1.5 µm is demonstrated experimentally. It is based on cascaded microring resonators (CMRRs) and the Vernier effect (VE). The architecture consists of two microring resonators (MRRs) connected via a common waveguide; two waveguides were added for the interrogation of CMRRs. The free spectral ranges of both MRRs are slightly different in order to activate the VE, which is known to enhance the sensitivity in optical sensors. CMRRs were fabricated on a silicon nitride (SiN) platform. Two types of buffer layers-benzocyclobutene (BCB) polymer and thermal silicon oxide (SiOx)-were tested. A study of CMRRs was carried out with three structures of different structural parameters. The experimental results show good agreement with the theoretical analysis. This approach is promising for the fabrication of highly sensitive optical sensors in wide operating wavelength range.