Method and apparatus for determining ratio of core radius to cladding radius in clad optical fibers

Claim 3

Δθ is a constant that is substantially the difference between θ p and the angle θ c where modulation begins, and m 1 is the refractive index of the cladding.

Claim 4

Δθ is a constant that is substantially the difference between θ p and the angle θ c where modulation begins, and m 1 is the refractive index of the cladding.

Claim 5

The method of claim 1 wherein the detecting step comprises: converting the scattering pattern into a time-varying electrical signal; filtering the time-varying signal to isolate the modulation component; and timing the interval from the start of the time-varying signal to the maximum of the modulation component, the length of the interval being proportional to the angle θ p .

Claim 6

Apparatus for determining the ratio of the core radius to the cladding radius, A/B, of a clad optical fiber, which comprises: a source of monochromatic, coherent light directed at the fiber to produce a far-field scattering pattern including contributions from portions of the beam reflected by the fiber, portions of the beam refracted by both the core and the cladding of the fiber, and portions of the beam refracted only by the cladding of the fiber; means for detecting a scattering angle, θ p , at which the maximum of a fringe modulation component occurs in the scattering pattern; and means for converting the detected scattering angle, θ p , into the ratio A/B from the relationship: A/B = sin [(θ.sub.p - Δθ)/2]/√m.sub.1.sup.2 + 1 - 2m.sub.1 cos [(θ.sub.p - Δθ)/2] where Δθ is a constant that is substantially the difference between θ p and the angle θ c where modulation begins, and m 1 is the refractive index of the cladding.

Claim 7

Apparatus for determining the ratio of the core radius to the cladding radius, A/B, of a clad optical fiber, which comprises: a source of monochromatic, coherent light directed at the fiber to produce a far-field scattering pattern including contributions from portions of the beam reflected by the fiber, portions of the beam refracted by both the core and the cladding of the fiber, and portions of the beam refracted only by the cladding of the fiber; means for detecting a scattering angle, θ p , at which the maximum of a fringe modulation component occurs in the scattering pattern; and means for converting the detected scattering angle, θ p , into the ratio A/B from the relationship: A/B = sin [(θ.sub.p - Δθ)/2]/√m.sub.1.sup.2 + 1 - 2m.sub.1 cos [(θ.sub.p - Δθ)/2] where Δθ is a constant that is substantially the difference between θ p and the angle θ c where modulation begins, and m 1 is the refractive index of the cladding.

Claim 8

The apparatus of claim 3 wherein the means for detecting comprises: means for converting the scattering pattern into a time-varying electrical signal; a filter connected to the converting means for isolating the modulation component of the time-varying signal; and means for timing the interval from the start of the time-varying signal to the peak of the modulation component, the length of the interval being proportional to the angle θ p .