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Measurement of the Refractive Index Profile of Polymer Planar Optical Waveguides using Optical Coherence Tomography

Author(s): David Ives
Affiliation(s): National Physical Laboratory

Topic: 1. Interferometry & Optical Testing Techniques
Presentation: Oral

Polymer planar optical waveguides fabricated onto electrical printed circuit boards are receiving great interest as a technology to produce an optical printed circuit board, OPCB, for use as computer backplanes. The measurement of the refractive index profile of the polymer planar optical waveguides is required to better understand and model the properties of these waveguides. In this paper optical coherence tomography, OCT is used to measure the refractive index profile of a (~1mm) cross section slice of the polymer planar optical waveguide. A Fourier domain OCT system utilising a scanning optical fibre based Michelson interferometer operating near 850nm is used. The interferometer is scanned across the cross section of the polymer planar waveguide to measure the profile of the apparent optical thickness of the slice. The actual thickness of the slice is obtained by using the interferometer as a scanning confocal microscope. The ratio of optical thickness profile to actual thickness gives the group refractive index profile of the polymer planar waveguide. The paper will also discuss the trade off between the x-y resolution in the profile and the divergence of the probe beam and the conversion of group refractive index to phase refractive index.