Micro-fiber inclinometer based on deformation of FBG

Abstract

ABSTRACT We propose and experimentally demonstrate a compact in-line micro-fiber inclinometer based on deformation of FBG, where the micro-fiber FBG beam is fabricated by special chemical etching method and the fiber pendulum is gained by splicing a section of hollow core fiber filling with tin to the end of the micro-fiber beam. The experiment results show that as the inclination angle increasing from0 0 to 20 0 , the increments of the transmission loss and Bragg wavelength of the sensor are 1.81dB, and 0.035nm, respectively. Simultaneously, the change of the bandwidth at -25dBm increases linearly from 0.86nm to 1.048nm and the bandwidth sensitivity to inclination angle is 7.24pm/deg. On the other hand, temperature cross issue is solved by monitoring the bandwidth at -25dBm because the bandwidth sensitivity to temperature is 0.089pm/ from 20 to 200 . Key Words: fiber sensor, micro fiber, inclination angle, FBG. 1. INTRODUCTION Inclination tests are not only in high demand for applications in monitoring the health of various civil infrastructures such as buildings, bridges, dams, tunnel, etc., but also play a major role in mechanical, instrumentation, robotics, aeronautical engineering applications. Fiber optics inclinometer s have been extensively investigated in recent years due to the advantages of high sensitivity, small size, immune to electromagnetic interference, etc. All of fiber optical inclinometers reported can be classified into four types: forward propagating configurations [1], mechanical force-transfer components [2-6], special fibers [7-10], and tilt FBG [11]. Forward propagating inclinometers based on LPFG and taper have high sensitivity but the sensors are fit for transmission configurations, not prefer-able for single-ended sensor applications, and cross sensitivity is another unavoidable problem for LPFG. A well-established approach to address the problems is to stick FBGs to special mechanical force-transfer components such as pendulums [2-5], and transmissive grating panel [6]. This approach is reflective, and can easily be used to detect multi-dimensional inclination. However, the inclinometers based on mechanical components are bulk, difficult to be embedded into the objects, and normally suffer from unwanted mechanical fri ctions, rotations, and instabilities. A more common approach is to use some special fibers written FBG, such as four-core fiber [8-9], eccentric -core fiber [10], and D-shape fiber [7]. This kind of inclinometers is reflective, small size, but difficult to be spliced with ordinary single-mode fibers (SMFs). Simultaneously, high cost is the common problem in manufacture practices. Another attractive approach is to design inclinometers based on TFBG, but the “ghost” mode resonance of TFBG consists of several low-order cladding modes, which introduces additional complexity for a demodulating systems. In 2013, a smart-structure inclinometer based on etched fiber and FBG reflector was reported [12], the sensor is reflective, small size, simple for fabrication and demodulation, but the sensitivity is low in the tilt range from 0