Study of microbubble defects in high-NA silicate-glass multi-core imaging fibers fabricated by the stack-and-draw method

The fabrication of multicore imaging fiber (MCIF)/fiber bundle by the stack-and-draw method is favorable to achieve a hyperfine spatial imaging resolution without the rise of lattice defectw, such as core breakage and dislocation. MCIFs made of silicate glasses as host materials usually present a high numerical aperture (NA), lower bend loss, and low inter-core crosstalk, giving an excellent imaging capability. In this paper, we focus on the microbubble defect (MD) in the high-NA silicate-glass MCIF fabricated by the stack-and-draw method. MDs are a type of local defect in a scale of micrometers or smaller, distributed randomly along the fiber length. Some MD would cause the abrupt variation of the core shape in the neighbor, which gives rise to a local scattering loss up to 10³dB/m according to the numerical simulation. The origin of MD is still uncertain, and our investigation shows that MD could possibly be mitigated or even eliminated in principle by minimizing the difference in softening the temperature between core and cladding glasses.