Box-like spectral output of nested ring feedback Mach-Zehnder interferometer

We propose for the first time, a newly configured device based on nested ring feedback Mach-Zehnder interferometer structure (Nested RFMZI). The analysis is based on the transfer matrix method. We use a systematic bottom-up approach starting from a conventional ring-enhanced MZI (REMZI), ring-feedback MZI (RFMZI), showing how the concept evolves into the design of the nested RFMZI. Uniquely, the nested RFMZI can be designed to yield a box-like transmission output, potentially useful for some sensing, switching and filtering applications.