Optical sensor for measurement of roll + pitch + yaw angles over large distances with high accuracy

There are applications, where the relative orientation, i.e. the roll-, pitch-, yaw angles, between a reference system and a far distant object system must be known. If the systems are closed together, for example, the rotational encoder is a standard instrument to measure the roll angle. For large distances (up to intersatellite distances) this optical sensor is able to measure the roll angle between both systems with an accuracy of about 1 arcsec within a range of plus or minus 30 degrees. The measurement principle is based on the reception and evaluation of the transmitted polarization plane according to the law of Malus. Replacing one photodiode with a position- sensing detector (PSD), the other two degrees of freedom can be also measured with similar accuracy within a range of about plus or minus 5 degrees. The present sensor principle is characterized by the application of amplitude- and polarization modulation with two perpendicular linear polarized laser diodes in the transmitter and evaluation of the signals with a suitable algorithm. The advantage of the sensor is that it becomes insensitive to stray light, intensity fluctuations of the laser diodes, responsivity fluctuations of the photodiodes and the p-s transmission splitting due to non-perpendicular incident light.