Recently, a research team led by Dr. YU Fei from the Shanghai Institute of Optics and Mechanics, Chinese Academy of Sciences, achieved a new research progress on microbubble defects in high-numerical-aperture multi-core imaging fibers. The results were published in Optics Express entitled “Study of microbubble defects in high-NA silicate-glass multi-core imaging fibers fabricated by the stack-and-draw method.” 

The use of silicate glass can enhance the numerical aperture of optical fibers, enabling the reduction of core size and minimizing core-to-core crosstalk, thereby serving as an effective means to achieve high-resolution optical fibers. However, multi-core imaging fibers made from silicate glass systems exhibit numerous imaging defects, which hinder further development of optical fibers and endoscopic imaging.

The research team investigated the relationship between microbubbles in optical fibers and imaging defects from both theoretical and experimental perspectives. Through destructive and non-destructive testing, they discovered a correlation between microbubbles remaining in the optical fiber and dark spots at the output end. By establishing a finite element model, they concluded that deformation of the fiber core results in extremely high loss (>500 dB/m), revealing that the compression of microbubbles on the fiber core causing localized high loss is the primary cause of defects. 

By replacing the core and cladding glass with materials that have more compatible thermal properties, the orderly expulsion of gas during fiber drawing was promoted, significantly reducing the formation of microbubble defects and effectively improving imaging quality. High numerical aperture multi-core imaging fibers with fewer dark spots were obtained. 

This work provides valuable reference for the fabrication of high numerical aperture imaging fibers and is expected to be applied in ultra-fine fiber endoscopes.  

Figure 1. Numerical simulation of loss caused by microbubble defects. (a) Reconstructed model of the deformed fiber core; (b) Power evolution in fiber cores with different degrees of deformation; (c) Electric field mode of the deformed fiber.

Figure 2. (a) Microscopic image, (b) one-meter-long transmission pattern, and (c) one-meter-long transmission image of the fiber before optimization; (d) microscopic image, (e) one-meter-long transmission pattern, and (f) one-meter-long transmission image of the fiber after optimization.

Article link: https://doi.org/10.1364/OE.559798

Contact: YU Fei

Advanced Laser and Optoelectronic Functional Materials Department,

Shanghai Institute of Optics and Fine Mechanics, CAS

Email: yufei@siom.ac.cn