Improvement of transmittance homogeneity via coating anti-Gaussian chromium films on tapered optical fibre arrays

The transmittance inhomogeneity of Tapered Optical Fibre Arrays (TOFAs) is well-recognized to attenuate edge signal, reduce detective sensitivity and compress dynamic response range. A radial depth-varied coating scheme based on a ‘transmittance-film thickness’ digital correlation model was proposed to improve the transmittance inhomogeneity of TOFA. Considering the characteristic that TOFAs exhibit a Gaussian distribution in their inherent transmittance, a volute mask with spiral gradient openings was first designed. This mask was then integrated with a self-developed rotating coating device to build a dynamically coordinated deposition system. The anti-Gaussian films was successfully fabricated by the integrated depositing system. The microscopic characterization by TEM and SEM illustrates the nonlinear and precise control on the thickness of the metallic chromium film from the center to the edge. The experimental results show the transmittance inhomogeneity of TOFAs coated by anti-Gaussian film is decreased from originally ranging from 4.21% to 11.872% to a minimum of 1.422%. It is confirmed that the prepared high-quality anti-Gaussian film effectively compensate transmittance.