Fig. 3.

Demonstration for the process of volumetric fusion, taking the fusion of multi-focus fiber as an example. $f_1$ and $f_2$ are the two vertically tilted fibers. ${\mathrm{ML}}_{P_1}$ and ${\mathrm{ML}}_{P_2}$ are the discrete approximation of ${\nabla }_M^2$ for $P_1$ and$P_2$, respectively. The yellow dashed lines in IDM and FDM indicate the position of fibers $f_1$ and $f_2$.