Measuring the Widths of Fibre Optics by Lateral Illumination – PR4

Light from a He-Ne laser is shone through the side of a fibre optic sample, which, according to Babinet’s principle, should produce a similar diffraction pattern to a slit or wire of the same width. By producing a calibration curve of diffraction pattern periodicity and known wire diameters, the width of the fibres could be determined from their diffraction pattern to within 1% of their literature value, consistent with the widely accepted manufacturing uncertainty. The technique could be used to simultaneously measure the core, fibre and plastic coating diameters.

Babinet’s principle

In physics, Babinet’s principle states that the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity. It was formulated in the 1800s by French physicist Jacques Babinet.

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