5.6 - Self-aligning optical beam waveguides+C6553

Previous experiments with a lens-type beam waveguide have demonstrated the applicability of such guides to efficient long distance transmission at optical frequencies. In practical applications it will be necessary to automatically compensate for movements of the ground which would misalign the guide and thus cause increased transmission loss. In order to investigate the practicability of "self-aligning" optical beam waveguides the available experimental guide was modified by adding a sensing device at each lens which indicates any displacement of the beam from the lens center. The displacement information is used to move the preceding lens in such a direction that the beam displacement is reduced. The automatic alignment procedure consists of sequential probing of the beam position at each lens and the corresponding corrective movement of the preceding lens. This procedure maintains essentially the same light path between the end points of the guide, independent of the movements of the ground. The maximum lateral excursions of the beam from the ideal path which occur in the present installation of one kilometer length are less than one millimeter and have no effect on the transmission loss. This alignment accuracy could be greatly increased, which might be of interest for geological measurements concerning movements in the Earth's crust.