1：Experimental Design and Method Selection:

The study involves the fine tuning of interfacial reaction between the core and cladding of the fiber via control of the viscosity of the melt.

2：Sample Selection and Data Sources:

A preform with silica as clad tube and multicomponent K–Nb–Si system as core material was employed.

3：List of Experimental Equipment and Materials:

KNbO3 crystal, silica cylindrical tube, ZEISS Merlin field-emission scanning electron microscope, electron probe micro-analyzer (EPMA-1600), Renishaw InVia spectrometer, optical microscope equipped with a charge coupled device (CCD), fiber optic spectrometer (Ocean optics, Maya2000, Pro).

4：Experimental Procedures and Operational Workflow:

The preform was drawn into fibers at the drawing temperature of about 1900°C by using the melt-in-tube technique with a 30 m min?1 drawing speed. The precursor fibers were heat-treated at 900°C for 10 h.

5：Data Analysis Methods:

Microstructures were studied using SEM and EPMA. Chemical bonding analyses were performed using micro-Raman spectroscopy. Optical properties were analyzed using an optical microscope and fiber optic spectrometer.