An electronic technique to make fringe displacement measurements on the output field of an interference microscope to 1/1000 of a fringe, not including systematic errors, is described. The method, based upon line‐selected video signal analysis, is applied to the evaluation of the refractive index profile of a graded index optical fiber. The index difference at a given point between the core and cladding is determined to better than 1 part in 105, implying a precision in the profile parameter α of ±0.005, an order of magnitude better than existing techniques.
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© 1978 American Institute of Physics.
1978
American Institute of Physics
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