The irreversible transformation of a tellurum oxide glass layer inserted between two ends of two silica glass optical fibers was monitored via the intensity of a light passed through the circuit. This structure is used for a heat-induced optical fuse after the soft glass layer has been coated with a light absorber. Heat-induced breakage occurred when the glass crystallized or flowed in the presence of a shearing stress. Without the stress, the optical link was maintained through the glass melt but suddenly broke due to the crystallization. Contrary to this, the stress deformed the glass bridge and broke the optical link less than 0.4 s. Thus, the shearing stress at the splicing point helps the device respond immediately and reliably.