1 research outputs found
Online measurement of optical fibre geometry during manufacturing
Online measurement of diameters and concentricities of optical fibre layers,
and the coating layer in particular, is one of the challenges in fibre
manufacturing. Currently available instruments can measure concentricity and
diameter of layers offline, and are not suitable for precise monitoring or
control of the manufacturing process in real time. In this work, we use two
laser beams, positioned orthogonally to illuminate the fibre from two sides,
and calculate deviations from the expected geometry by analysing the scattering
pattern. To measure the diffraction pattern we use two 8K linear array
detectors, with the scattered light incident directly on the sensors. Each
detector is capturing approximately 90 degree angular range directly behind the
fibre. The two measurement channels are positioned at different heights. The
scattered pattern is modelled mathematically with finite-element and
Fourier-modal methods, with various diameter and concentricity deviations. The
sensitivities of the changes in the scattering pattern are identified in
respect to these deviations. Since calculations are computationally intensive,
the sensitivities are pre-calculated in advance, and the real-time measurement
is based on pattern recognition. The symmetry of the pattern is used to
differentiate between diameter and concentricity variations. We performed
online measurements with the prototype instrument in production conditions, and
show that this method is sensitive enough to measure deviations of under 1
{\mu}m in diameter and concentricity of the coating layer.Comment: Proceedings article, SPIE conference "Fiber Lasers and Glass
Photonics: Materials through Applications