Patent ID: 6441907
Filing Date: 2002-08-27
Classification: G01C

Abstract:
An optical interferometric sensing apparatus for measuring a refractive index of an object, comprising:a ring laser cavity for generating four laser beams, two of said four laser beams propagating away from said ring laser cavity in a first direction and the remaining two laser beams propagating away from said ring laser cavity respectively in second and third directions; two external mirrors, said two laser beams propagating in the first direction being reflected off from the respective external mirrors to be directed back to said ring laser cavity, said object being placed along an optical path between said ring laser cavity and one of said two external mirrors; two sensors respectively positioned to measure intensities of said remaining two laser beams; and means for calculating a refractive index of said object based on the measured intensities, wherein the apparatus operates in four operational modes when the optical path lengths between said ring laser cavity and said two external mirrors are respectively l1 and l2, and the four operational modes include: one of the optical path lengths l1 and l2 is varied, the optical path lengths l1 and l2 are varied while maintaining Â±(l1âˆ’l2) constant, the optical path lengths l1 and l2 are varied while maintaining (l1+l2) constant, and the optical path lengths l1 and l2 are independently varied.