Microstructure analysis in the coupling region of fiber coupler with a novel electrical micro-heater

Abstract

Fused-tapered fiber coupler is widely used in optical-fiber communication, optical-fiber sensor and optical signal processing. Its optical performance is mainly determined by the glass properties in the coupling region. In this study, the effect of fused biconical taper (FBT) process on glass microstructure of fiber coupler was investigated by testing the microstructure of the cross-section of coupling region. The fiber coupler is fabricated with a novel home-designed electrical heater. Our experimental results show that the boundary between fiber core and fiber cladding become vague or indistinct after FBT under transmission electron microscopy (TEM) and Ge 2+ in fiber core diffuses into fiber cladding. Crystallizations are observed in coupling region under scanning electron microscope (SEM) and microscopic infrared (IR), and the micro crystallizations become smaller with the drawing speed increasing. The wave number of fiberglass increases after FBT and it is in proportion to the drawing speed. The analysis of the microstructure in the coupling region explored the mechanism of the improvement in the performance of fiber couplers which can be used for the guidance of fabrication process.