Enhanced transverse wavelength tuning of fiber Bragg gratings for sensing applications

Abstract

Fiber Bragg grating (FBG) based strain sensors have found a variety of applications in the last two decades. Most of these applications utilize the wavelength tuning of FBGs through an axially induced strain because of the high axial load sensitivity in comparison to lateral loading. However, wavelength tuning through lateral or transverse loading is attractive for applications like structural health monitoring, damage detection etc, owing to the flexibility in mounting or embedding the sensor. The wavelength tuning of the FBG sensors through lateral loading has the advantage of easy surface mounting, ruggedness, long term stability, structural integrity and more resistant to vibration. However, the potentials of wavelength tuning through lateral loading are yet to be utilized by overcoming its inherent limitations of low lateral pressure sensitivity, narrow tuning range and stress induced birefringence. In order to understand these problems, various studies regarding the lateral loading process are performed initially. These studies include analysis of influence of the pressurizing media (or contact media) and contact conditions on the wavelength response characteristics of the FBGs. It is found that the material of the pressurizing media, its configuration and the contact friction play major roles in lateral pressure tuning (LPT) process and significant enhancement in performance can be achieved by optimizing these parameters. The lateral pressure sensitivity is high for a contact media with low value of Young's modulus. The sensitivity also increases with both the thickness of the contact plate and the contact friction between the fiber and the contact media. However, using an optimized contact media always may not be feasible in all working conditions. ni