Filter based MZI Gain Responses (MZ8, MZ9) Here a demonstration of a filter response is shown by cascading two interferometers and considering no loss. Figure \ref{fig:mzi8-9}(a) shows the response when two interferometers with similar path length difference are chain together. The response is a bit similar to MZI6 interferometer. However, figure \ref{fig:mzi8-9}(b) shows an interesting response where clearly the transmission peaks are a bit narrower. If at each stage of interferometers the path difference follows a geometric progression i.e. \(\Delta L\), \(2\Delta L\), \(4\Delta L\), ... then low passband loss occurs and clearly defined peaks are obtained.\cite{madsen1999optical} Another interesting application for these filters is as a channel selector or de-multiplexer. By cascading multiples of these devices, one can narrowly select closely spaced optical channels. \cite{Agrawal_2005}