Apparatus for measuring the refractive index of an optical fiber

摘要

The apparatus described basically includes a vessel (10) which has a horizontal transparent window (11) and contains an index liquid (12). An optical fiber (13) is mounted in this vessel perpendicular to the window (11). Light (14) is launched and focused by a condenser (15) onto fiber (13). The light cone of aperture angle (2 beta ) due to the guided and leaky modes is eliminated using an annular mirror (16) that reflects the remaining portion of the aperture light cone (2 alpha ) escaping laterally from the fiber. This light reflected by the mirror (16) is focused by an annular condenser (18) and reflected onto a detector (20) by a flat mirror (19) with a hole in the center. Measuring the amount of light received by the detector (20) allows the refractive index of the fiber to be determined.