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Dual frequency sweeping interferometry for absolute metrology of long distances

A. Cabral, M. Abreu, J. M. Rebordão

Frequency sweeping interferometry(FSI) is a technique where absolute distance measurements are made without ambiguity, using synthetic wavelengths resulting from frequency sweeps. Accuracy is mainly dependent on the synthetic wavelength measurement using a Fabry–Pérot interferometer to count resonances as frequency sweeps. Measurement uncertainty increases with distance due to propagation of uncertainty in the synthetic wavelength measurement. For large distances, the number of fringes dominates performance, leading to a linear decrease of accuracy with range. To overcome this problem, the dual FSI concept was introduced, where the measurement process for large distances is reduced to the close-range case, by limiting the interferometer optical path difference. This is achieved by increasing the reference arm with a long reference fiber, and using an ancillary interferometer to calibrate the fiber length continuously. This dual FSI concept was implemented and fully tested in view of ESA-PROBA3 space mission. The sensor is composed of an external cavity diode laser, a high-finesse Fabry–Pérot interferometer, and a dual measurement system. Accuracies better than 32µm for a measurement range from 51to61m were achieved using a reference fiber with 71m , while maintaining the reduced complexity inherent to FSI technique, which is mandatory for space applications.

Optical Engineering
Volume 49, Number 8, Page 085601_1
2010 August

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia