Fiberoptic displacement sensor using interferometric techniques

A method of detecting a location of an object comprising providing an optical fiber having a light inlet end and a light discharge end, providing a light source at the light inlet end for transmitting light along the fiber, said light source having a primary wave length .lambda., locating the light discharge end adjacent to but spaced from the object by a distance D, allowing variations in the distance D, defining a fiber-to-medium interface at the discharge end and a medium-to-object interface at the object such that light transmitted along the optical fiber from the inlet end to the discharge end has a first part which is reflected from the fiber-to-medium interface back along the fiber and a second part which is reflected from the medium-to-object interface back into and along the fiber, the distance D between the object and the discharge end being arranged relative to the primary wave length .lambda. such that the first part and the second part interfere to form interference patterns having variation in light intensity depending upon a phase difference therebetween caused by said variations in the distance D, detecting with respect to time said variations in the intensity of light reflected, causing a cyclical variation in a path length of the second part of the light, the cyclical variation having a predetermined frequency and a predetermined amplitude, and analyzing the variation in the intensity of light reflected to determine said variations in the distance D.