Fiber-optic interferometric displacement sensor

An interferometric displacement sensor is described, executed on the basis of single-mode fiber-optic elements. The sensor is simple, accurate, and permits contactless measurement in sites with difficult access. An expression is derived relating the interferogram luminosity with the distance to the mirror being displaced, while the absolute value of the displacement is determined by the number of interference fringes by which the interferogram is shifted. Experimental determination of luminosity as a function of displacement are reported which indicate maximal displacements of 17 mm can be measured, although methods of increasing the maximal displacement are discussed.