Five-step phase-shifting white-light interferometry for the measurement of fiber optic extrinsic Fabry–Perot interferometers

Five-step phase-shifting white-light interferometry is presented for interrogating the absolute cavity length of the fiber optic extrinsic Fabry-Perot interferometer (EFPI). It combines ideas of phase-shifting interferometry and white-light interferometry (WLI) to extend the measurement range of fiber optic WLI. Five sub-interferograms intercepted from the white-light optical spectrum are used to recover the optical path difference (OPD) of the EFPI. This method is demonstrated to interrogate a wider range of OPD. The experimental results show that the measurement resolution ranges from 0.5 μm to 5 μm with cavity length ranges from 16 μm to 12,402 μm, and it has a great advantage in measuring EFPIs with short cavity lengths.