Modeling of Fabry-Perot Micro Cavities Under Partial Spatial Coherence Illumination Using Multimode Optical Fibers

Extrinsic Fiber Fabry-Perot Interferometers (EFFPIs) are used for a wide range of applications such as sensors and optical filters. They are usually built using single mode (SM) fibers as they provide better performance and sensitivity when compared to multi-mode (MM) fibers. However, SM fibers are more sensitive to misalignment and MM fiber has a much higher capacity to handle wide spectral range optical power. In this work, a model is developed and experimentally examined for MM fibers based EFFPIs. The model is based on considering the MM fiber as a partial coherent source emitting a Gaussian-Schell beam. The model is used to predict the EFFPIs response and extracted parameters such as finesse, visibility and insertion loss and to study their variation with the cavity length. It can be used for both low and high reflectivity cavities. An experimental setup is formed using two Bragg-coated MM fibers having a numerical aperture (NA) of 0.22 and a core diameter of 62.5 μm, the coating has a high reflectivity above 0.98 over a wavelength range extending from 1490 nm to 1600 nm. The model output is compared with the experimental results and a good agreement is observed.