Compensation Scheme for Differential Fiber Reflectometers
Original Publication Date: 1985-Jun-01
Included in the Prior Art Database: 2005-Feb-18
The differential fiber sensor of Fig. 1 is a high resolution sensor of lateral displacements of a reflecting feature on a flat substrate. Scanning through a thin line, one measures the 'S'-shaped characteristic of Fig. 2. However, angular displacement of the probe with respect to the substrate normally gives an output indistinguishable from lateral displacement, leading to errors. Therefore, the compensated sensor of Fig. 3 is proposed. Two identical sensors 12 and 14, are used, sourced from the same (LED). Sensor 14 views the reflecting line feature as before. The second, reference, sensor 12 views a uniform reflective pad, filling its entire field. The second sensor's outputs may be used to measure both the sensor height and the angular orientation, independent of lateral position.