Laser range-finding: Global characterization of the optical head, implementation of measurement methods.

Whatever laser range-finding technique is used, the operation principle is based on optical information coding and transmission. Indeed, the optical head represents the common point within the whole of telemetric methods. So, its precise characterization presents a major interest. The emission part is performed by a laser diode and the reception by an avalanche photodiode coupled with filtering and RF amplification. The optical path is along coaxial alignment if an appropriate geometry is chosen. The whole system may be considered as a quadripole with the emitter as the input and the receptor as the output. Therefore, the network analyzer is particularly adapted to a global study of such a quadripole. With a measurement protocol, the performances of the optical head can be then evaluated in term of optical and electronic properties. Nevertheless, according to the great variety of ranges to be measured, many range-finding methods can be used, as the Frequency Modulated Continuous Wave (FMCW) radar ranging method, the phase-shift measurements, either with heterodyne method or direct synchronous detection. Whereas two of these, the FMCW or the heterodyne phase detection, have already been developed in our laboratory, we only introduce as a new method the synchronous detection.