Abstract
A study has been made of the principles involved in displacement measurement using optical methods, with particular emphasis on intensity - modulated laser beam techniques. Some of the compromises in performance possible in differing situations are discussed. Previous research has dealt with an approach using coherent optical interference. The two methods are compared theoretically, and it is shown that certain advantages are possessed by the Modulated Beam technique. An important component in the system discussed is the Intensity Modulator. Methods of electro-optic modulation have been studied, and a modulator using Lithium Niobate has been designed and built. It requires low modulation voltages, operates in the v. h. f. region, and has the important advantage over similar modulators in that it is completely insensitive to temperature. A theoretical analysis has been carried out on the design of a modulated optical carrier system, which includes a novel approach to the measurement of displacement and distance. Experimental measurements and results from a practical system, using an external target at 60 metres range, are described and shown to compare satisfactorily with theoretical predictions.