High-accuracy Fabry–Perot displacement interferometry using fiber lasers

Abstract

We describe ongoing work in a Fabry-Perot interferometry system designed to measure displacements over a range of 50 mm with sub-pm uncertainty. The apparatus involves probing two nearby modes of the Fabry-Perot cavity with narrow-linewidth fiber telecom lasers and measuring both the mode spacing and the absolute mode frequencies relative to a third, frequency-stabilized, fiber laser. We explore the improvement in resolution obtained as the frequency separation between the two modes is increased and employ an internal consistency requirement to infer the magnitude of residual systematic errors. The measurement uncertainty is sufficiently small that we are easily able to see the Gouy phase shift as the cavity length is changed over several millimeters.

Accurate Gouy phase measurement in an astigmatic optical cavity

“…Additional sources of uncertainty are the presence of the nearby TEM 20 and TEM 02 modes (Fig. 2), which slightly shift the laser lock point from the TEM 11 resonance frequency, and parasitic cavities [25,26] which can also shift the resonances. We estimate (type B evaluation) these contributions to be 0:03 lrad and 0:06 lrad, respectively.…”

Dimensional stability validation and sensor calibration with sub-nanometer accuracy

“…This may facilitate larger measurement sampling rate and thus anticipate thermomechanical instability for otherwise longer lasting calibration sequences (cf. comb usage in [7,14]). Ambient climate conditions, such as humidity effects [15] or pressure fluctuations [16] limit the ultimately achievable measurement uncertainty.…”

“…Versatile configurations and large displacement range are supported. Even higher sensitivity and precision for displacement measurement is supported by Fabry-Pérot interferometry (FPI), with high frequency selectivity of the optical cavity resonance [7][8][9][10]. FPI is particularly useful for the calibration of ultra-precision displacement sensors due to the versatility in the translation-actuated measurement interface, e.g.…”

New simple optical sensor: From nanometer resolution to centimeter displacement range

“…Fabry-Perot interferometers present high ratio range over resolution. Some of them reach sub-nanometric uncertainties over centimeters but to the detriment of the complexity [5]. Inductive sensors have been also developed but nanometric resolution remains difficult to reach because of magnetic disturbances.…”