Proposal of an OADM configuration with ultra-large FSR combining ring resonators and photonic bandgap structures

Optical Add-Drop Multiplexers (OADMs) allow extracting and inserting data channels in WDM, user access and interconnection applications. A great interest is focused on building small footprint integrated OADMs, which can be achieved using compact ring resonators (RR). Free spectral range (FSR) values up to some tens of nanometers can be obtained by using RR with small radius or multi-stage configurations, but structural parameters are pushed to the limit in these configurations leading to very tight fabrication requirements. We propose and numerically study a novel configuration of RR-based OADM where the FSR is hugely increased to values higher than 140 nm by combining RRs with photonic bandgap structures, which remove the non-desired resonances inside the RR. Moreover, this structure can be hitless reconfigured, what is difficult to achieve in actual configurations.