Optical power variation only Amplitude to phase conversion issue in telemetry CONTEXT/OBJECTIVES: This work was realized within JRPs « SURVEYING »(SIB-60) and « LUMINAR » (IND-53). In both projects a compensation of air temperature and pressure variation is targeted using two different wavelengths (1550 nm and 780 nm) and air index dispersion. A first step is the realization of a robust and simple one wavelength telemeter at 1550 nm, with a resolution below 5 µm indoor. It turns out that the amplitude to phase conversion in photodetectors and electronic stage is a critical issue that has to be considered PRINCIPLE OF THE TELEMETER INDOOR MEASUREMENTS OUTDOOR MEASUREMENTS in red = amplitudes equal to 7.9dB ± 2 dB Std over 50 points between 11 & 24 µm Standard deviation = 38 µm Experimental setup at 1550nm Optical switch: every second we compare the measured distance to a reference distance that do not vary during the measurement process. Thus, every variations observed on the reference path are interpreted as drifts from the system (for instance temperature evolution in amplifiers) and are so removed from the measured distance. Joffray Guillory 1, Jorge Garcia-Marquez 1, Anne-Françoise Obaton 1, Christophe Alexandre 2, Daniel Truong 1 and Jean-Pierre Wallerand 1*. 1 Laboratoire Commun de Métrologie LNE-CNAM (LCM), 1 rue Gaston Boissier, PARIS 2 Centre d’études et de recherche en informatique et communications (CEDRIC), CNAM, 292 rue Saint-Martin, PARIS * Corresponding author: AMPLITUDE TO PHASE CONVERSION Optical and RF power variation Metal semi conductor metal photdetector (Hamamatsu G ) InGaAs avalanche photodiode (Hamamatsu G ) Amplitude to phase variation conversion due to photodetector and electronic stage Metal semi conductor metal photodetectorInGaAs avalanche photodiode sunny day, 35°C, along an asphalt road. A selection of data within an amplitude interval of 4 dB greatly improves the robustness of the system. Avalanche photodetector is less sensitive to amplitude to phase conversion. In that case the global amplitude to phase conversion is essentially due to electronic stage (mixer+amplifiers) CONCLUSION/PERSPECTIVES: A robust and compact telemeter was realized at 1550 nm using off-the-shelf components from telecommunication industry. A resolution of 3 µm was obtained indoor using a modulation frequency of 1,3 GHz. Amplitude to phase conversion was minimized by a selection of measurement data comprised in a given amplitude interval. A measurement of up to 600 m outdoor was realized (limited by available distance). Next steps will be to increase the modulation frequency and to add a second wavelength (773 nm) to the system in order to compensate air index fluctuation due to pressure and temperature variation. Measurement during 90 mn over 2 m indoor. The modulation frequency was 1,3 GHz. The resolution (short term standard deviation) was approximately 3µm. Residual variations are due to uncompensated drifts in the optoelectronic system. In black: electronic signals. In orange: fibered system. In red: free space light. Over 400 m under favourable conditions: Over 100 m under unfavourable conditions: Selection of data JRP IND 53 This project is performed within the joint research projects SIB60 “Surveying” and IND53 “Luminar” of the European Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.