Fiber optic displacement sensor employing a graded index lens. 
A novel intensity modulated fiber optic displacement sensor based on the relative motion of an optical fiber and a graded index lens is described.  The technique allows the use of either single- or multimode optical fibers in either single or dual fiber configurations.  Displacement sensitivities of 25 A have been measured using 50-microm core diam multimode fibers, with a light emitting diode source.  Theoretical sensitivities of the order of 0.01 nm are predicted with the use of single-mode fibers.