Influencing mechanism of fiber deformation on mesh pattern noise in inverting-image fiber-optic arrays

Abstract

Inverting-image fiber-optic array (IIFOA) is an important optical element for transferring the inverted images at 180° with high resolution and contrast. Mesh pattern noise (MPN) generated at the boundary of the multi-multi fibers in IIFOA significantly deteriorates the imaging quality and detection accuracy. The unexpected deformation of the optical fibers at the boundary of multi-fiber is one of the main factors causing MPN. In this study, the brightness distribution of the optical fibers and the corresponding microstructure were characterized by high-resolution Lambert-light microscopy and scanning probe microscopy with laser scanning, respectively. The relative transmittance of the individual optical fibers located in the MPN zone was normalized and calculated, and the cross-sectional deformation coefficient (De) of optical fiber in the twisted zone was proposed. Furthermore, the relationship among De, the relative transmittance of optical fibers, and MPN of IIFOA was established. The results show that the relative transmittance of optical fibers indicates an initial decrease and a subsequent increase with the decrease of De in the MPN generated zone. When De of the optical fibers is within the range of [0.3497, 0.9225], the relative transmittance is no more than 96.74%. The aggregation and distribution of these optical fibers at the adjacent side of the multi-multi fiber boundary causes black mesh pattern noise. When De of the optical fibers is less than 0.3228, the relative transmittance is consistently higher than 3.26% of the non-deformed fibers owing to the enhanced crosstalk of the adjacent optical fibers and even the new imaging unit formed by bonding some core fibers. The aggregation and distribution of such optical fibers at the boundary causes white mesh pattern noise. When De is between 0.3228 and 0.3497, there is no MPN, but the resolution is significantly reduced. The research results provide data support and theoretical guidance for controlling defects such as MPN and transmittance inhomogeneity in IIFOA, thus enabling the improvement of the image quality of IIFOA.