“Absolute distance measurement using comb-referenced frequency sweeping interferometry”
“Mesure de distance absolue utilisant l’interférométrie à balayage de longueur d’onde étalonnée par un peigne de fréquences”
par Wenhui Yu, ICube équipe IPP
le mercredi 10 avril 2019 à 13h30, Amphithéâtre A301, Télécom Physique Strasbourg
In this thesis, we implemented a high-precision absolute distance measurement (ADM) system using frequency sweeping interferometry (FSI). The FSI technique requires the frequency tuning range of the swept laser to be measured with high accuracy and precision, which is challenging due to the lack of an easy way to measure the high frequency of a laser in real time. In this thesis, a frequency comb has been used as the ruler for measuring the frequency tuning range of the sweeping laser. The frequency calibration was realized by filtering the heterodyne signal between the sweeping laser and the comb lines using a narrow bandpass filter. This approach allows us to detect the calibration signal when the frequency of the sweeping laser is in the vicinity of a comb line. As the comb line space can be precisely measured or actively phase-locked against a stable radio-frequency (RF) oscillator, the tuning range of the sweeping laser could be measured with high accuracy. Specially, each two calibration peaks can be used in the calculation of distance, which we call ‘sub-measurements’ in a single sweeping. Combined with the large number of the comb lines, averaging of the sub-measurements improves greatly the measurement precision without multiple sweeping.
Experimental works based on the measurement concepts have been carried out. It shows that using the proposed measurement scheme can greatly improve the distance measurement precision. In one of the measurements, a precision of 30 nm for a distance around 0.8 m, corresponding to 37×10e-9 relative uncertainty has been achieved. The result was obtained based on a fringe counting signal processing method. The high precision was obtained thanks to the large number of sub-measurements and the stability of the evenly spaced comb lines. We have found that vibration measurement of the target can be also performed taking the advantage of the dense comb lines. A high sensitivity, limited by 1.7 nm noise RMS, of vibration measurement has been achieved. This result allows us to monitor the vibration of the target, which is an important issue of FSI technique.
Membres du jury :
– M. CHASSAGNE Luc, Professeur, Université Versailles Saint-Quentin – Rapporteur
– M. LINTZ Michel, Chargé de recherche, HDR, Observatoire de la Côte d’Azur Nice – Rapporteur
– M. SALVADE Yves, Professeur, Haute Ecole Arc Saint-Imier (Suisse) – Examinateur
– M. LEONARD Jérémie, Chargé de recherche, CNRS, Université de Strasbourg- Examinateur
– M. PFEIFFER Pierre, Maître de Conférences (HDR), Université de Strasbourg – Directeur de thèse
– M. FONTAINE Joël, Professeur, INSA de Strasbourg – Co-directeur de thèse