Study of macro-bending biconical tapered plastic optical fiber for relative humidity sensing

Purpose The purpose of this paper is to propose and optimize plastic optical fiber (POF) probe with macro-bending biconical tapered structure for the relative humidity (RH) sensing. Design/methodology/approach In this study, the principle is the evanescent wave power modulated by the ambient humidity. The probe is fabricated by using fused biconical taper and heat-setting method and then coated with a fluorescent moisture-sensitive film. Findings The probe’s sensing performance can be optimized by changing the probe’s curvature radius, biconical tapered transition length and taper waist diameter. The result shows that the sensitivity of the probe is up to 1.60 and 3.40 mV/ per cent, respectively, at low humidity (10-45 per cent) and high humidity (45-90 per cent). Also, this probe has good linearity, repeatability, photostability and long-term stability. Practical implications The proposed probe can improve the sensitivity and linearity of RH sensing without complex devices, which is necessary for mass production, remote measurement and convenient operation. Originality/value POF probe with macro-bending biconical tapered structure is investigated in this paper, which is proved to be effective in improving the sensitivity and linearity.

Movement Realization of a Novel Fused Biconical Taper System Based on Electrical Heater

A novel fused biconical taper system is developed based on electrical heating system. Its movement platforms are designed. The main drawing movement platform, heater movement platform and packaging movement platform are focused on analysis. Motion control program is developed based on Delphi 2006 according to its technological requirements. The experimental results show that the movement of the novel fused biconical taper system is very stable, and the optical fiber couplers fabricated with the novel system have the good optical performance and the good consistency in particular.

The Microstructure Evolution in Fused Region and Taper Region of Fibre Coupler

The fused region and the taper region of the optical fibre coupler were tested by atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The results indicated that the surface roughness increased after fused biconical taper (FBT), that is, the fused region possessed the highest toughness (about 70nm), the taper region is in a second position (about 40nm), and the bare fibre was relatively the lowest (about 10nm). Micro crystals were observed at the fused region and the amount of the micro crystals decreased with increasing the drawing speed. Micro cracks were observed at the taper region and the micro cracks became wide and deep with increasing the drawing speed. All these changes affected not only the optical performance such as excess loss and consistence, but also the reliability and stability. Therefore a fibre device with high quality required small drawbacks.