Fiber Bragg grating sensor system for dynamic strain measurement without optical fibers

Abstract

Fiber Bragg grating (FBG) sensor systems are being widely used as temperature measurement and strain measurement systems for aerospace structures, civil structures, and high rise buildings. However, the systems are rather complicated because the wavelength change must be measured using several kinds of optical filters such as Fabry-Perot filters, edge filters, and bandwidth filters. In this paper, FBG sensor without filter system is proposed. The system consists of SLD (Super Luminescence Diode), diode driver, FBG sensors and the photo diode as a detector. Neither Fabry-Perot filter nor edge filter is applied. SLD has its own intensity slope according to various wavelengths. The slope is very linear at certain wave length range. In the beam experiments, the 1525 nm center wavelength FBG is employed as a sensor and the grating shows good linear responses to the dynamic loads. The data compare to those of electric strain gauges. The system also has a potential to be multiplexed by the pulse modulations in the time domain. If the FBGs have different wavelengths, they can be placed in the same fiber and if the FBGs have the same wavelength, they must be in the separate optical fiber and connected with couplers in order to be multiplexed.