Rapid optical fiber delta measurement by refractive index tuning

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Abstract
A technique is presented for rapidly measuring Δ of optical fibers with profiles closely approximating n(r) = n(o) [1 − Δ(r/a)α], the Δ ≪ 1 limit of the two-parameter Gloge-Marcatili profile. Error analysis indicates an accuracy of about ±9%. The method is as follows: Using a Michelson interferometer together with a microscope, the transverse optical path through the center of a fiber immersed in index matching fluid is set equal to the optical path through the fluid. This is accomplished by varying the temperature of the fluid. The value of A can then be determined from a knowledge of the refractive index of the fluid inferred from temperature measurements. Good agreement is shown between A values measured by this technique and those measured by-two other interferometric techniques. The possible use of this method to determine a, or to determine the actual profile if it does not follow the assumed shape, is discussed.