In this work, it is reported that the interference pattern produced by an interferometer can be studied on the s-plane and its modulated function having three poles and two zeros over the imaginary axis. This is corroborated theoretically and experimentally using the interference pattern produced by a Fabry- Pérot interferometer based on Bragg gratings printed on the core of an optical fiber. From our theoretical and experimental work, it is confirmed that the poles and zeros are on the imaginary axis of the s-complex plane and their positions depend on the spatial frequency of the interference pattern. This is graphically displayed on a pole-zero map. In the theoretical analysis, three poles are localized at position $s_0=0$ and $s_{1,2}=\pm {\omega }_{\mathit{FP}}i$ while two zeros are localized at positions $s_{1,2}=\pm \frac{{\omega }_{\mathit{FP}}}{\sqrt{2}}i$. In our experiments, using the Fabry-Pérot interferometer whose cavity length is $L_{\mathit{FP}}\approx 1.58mm$, three poles are localized at position $s_0=0$ and $s_{1,2}=\pm 11.93irad/nm$ while two zeros are localized at positions $s_{1,2}=\pm \frac{11.93}{\sqrt{2}}irad/nm$, confirming the theory.

Our proposal finds practical application on signal demodulation for the interferometers and quasi-distributed sensor based on the interferometry.