This paper proposes a two-dimensional displacement sensor which is available to detect high speed phenomena such as high frequency vibrations. The sensor consists of a laser, polarisers, a beam splitter, solar cells and clean plates in which an index of double refraction varies in one direction. Since the clean plate as just mentioned has not been produced, this paper applies thin films sandwiched with a magnetic fluid, and the double refraction is generated by using permanent magnet. In this system, the laser beam propagating from the moving body is divided into two beams by a beam splitter, and the divided beams pass through the two clean plates whose refraction axes are in right angles with each other. An intensity of the laser beam after passing through the clean plate is detected by a solar cell. Then the position of each beam is decided by the intensity of the laser beam. Experimental tests have been performed to verify the principle as just mentioned.
