White-Light-Interferometry-Assisted Fabrication of Closely Matched Fiber-Optic Fabry–Perot Cavities

This work presents a method for fabricating multiple closely matched Fabry–Perot (FP) cavities by employing White Light Interferometry (WLI) to monitor cavity length in real time throughout the process. This approach allows direct tracking of the actual optical path difference during fabrication, using the same interrogator that will be employed during sensor operation. As a proof of concept, three FP cavities were fabricated and found to be closely matched through WLI measurements. Optical microscopy was additionally used to inspect the fabricated cavity geometry. The three fabricated cavities exhibited a mean measured length of 499.606 µm and a maximum cavity-to-cavity difference of 10 nm, indicating close agreement among the three samples; this limited dataset does not establish statistical reproducibility or nanometer-scale measurement uncertainty. The absolute cavity length remains dependent on the calibration uncertainty of the reference cavity.