A Single-Ended Ultra-Thin Spherical Microbubble Based on the Improved Critical-State Pressure-Assisted Arc Discharge Method

Wenfeng Guo,Jianxun Liu,Mengxing Huang,Gao Wang,Guanjun Wang,Jinrong Liu

doi:10.3390/coatings9020144

Abstract

Hollow core microbubble structures are good candidates for the construction of high performance whispering gallery microresonator and Fabry-Perot (FP) interference devices. In the previous reports, most of interest was just focused on the dual-ended microbubble, but not single-ended microbubble, which could be used for tip sensing or other special areas. The thickness, symmetry and uniformity of the single-ended microbubble in previous reports were far from idealization. Thus, a new ultra-thin single-ended spherical microbubble based on the improved critical-state pressure-assisted arc discharge method was proposed and fabricated firstly in this paper, which was fabricated simply by using a commercial fusion splicer. The improvement to former paper was using weak discharge and releasing pressure gradually during the discharging process. Thus, the negative influence of gravity towards bubble deformation was decreased, and the fabricated microbubble structure had a thin, smooth and uniform surface. By changing the arc discharge parameters and the fiber position, the wall thicknesses of the fabricated microbubble could reach the level of 2 μm or less. The fiber Fabry-Perot (FP) interference technique was also used to analyze the deformation characteristic of microbubble under difference filling pressures. Finding the ends of the microbubbles had a trend of elongation with axial compression when the filling pressure was increasing. Its sensitivity to the inner pressure of microbubble samples was about ~556 nm/MPa, the bubble wall thickness was only of about 2 μm. Besides, a high whispering gallery mode (WGM) quality factor that up to 107 was realized by using this microbubble-based resonator. To explain the upper phenomenon, the microbubble was modeled and simulated with the ANSYS software. Results of this study could be useful for developing new single-ended whispering gallery mode micro-cavity structure, pressure sensors, etc.

Highlights

Microbubble could be very useful in many optical fiber sensing applications [1]
It is found that for solid microsphere materials, the melt-shrinkage effect occurs during arc discharge, which results in a solid microsphere cavity with good smoothness and uniformity
This thin and uniform single-ended microbubble could be very useful for FP cavity-based pressure sensors and whispering gallery mode (WGM) based devices

Summary

Introduction

Microbubble could be very useful in many optical fiber sensing applications [1]. For example, a high sensitivity pressure sensor based on the Fabry-Perot (FP) interference could be realized by Coatings 2019, 9, 144; doi:10.3390/coatings9020144 www.mdpi.com/journal/coatings. Under the condition of critical-state pressure-assisted arc discharge by repeatedly regulating and controlling the parameters of discharge intensity, filled air pressure value, microbubble position and others, the microbubble film layer can be gradually thinned, and at the same time, the advantages of the traditional solid microsphere cavity are smooth, uniform and symmetry could be retained This improved critical-state pressure-assisted arc discharge method was proposed for fabricating ultra-thin single-ended hollow core microbubble structure here. This method possesses the merits of using weak discharge and releasing pressure gradually during the discharge process. The focus of this paper is to optimize the fabrication of single-ended bubbles using only the improved critical-state pressure-assisted arc discharge method at a very cheap cost

Fabrication Process and Results

Mechanical Properties and Analysis

Conclusions