Optics and Lasers in Engineering 122 (2019) 59–64 Contents lists available at ScienceDirect Optics and Lasers in Engineering journal homepage: www.elsevier.com/locate/optlaseng Chirped fiber Bragg grating coupled with a light emitting diode as FBG interrogator Muneesh Maheshwari a,b , Yaowen Yang a,b,∗ , Tanmay Chaturvedi b , Swee Chuan Tjin c a Maritime Institute, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore b School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore c The Photonics Institute, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore a r t i c l e i n f o Keywords: Chirped fiber Bragg grating (CFBG) Fiber Bragg grating (FBG) Light emitting diode (LED) Wireless sensing a b s t r a c t Due to rising demand for smart infrastructure systems, cost-effective, efficient and reliable sensing systems are needed more than ever. In this paper, a novel fiber Bragg grating (FBG) interrogation system is proposed in which very few optical components are employed. In the proposed system, light from an LED is coupled into a chirped (CFBG). The light transmitted through the CFBG is received by a photodiode to measure its power, which is interrogated to measure the change in strain or temperature in the CFBG. A highly stable current driver supplies current to the LED to generate a stable LED output. The presented system is of low power, simple, compact, robust and cost-effective with a strain measurement resolution of about 6 . The user convenience can be greatly enhanced by integrating the system with a wireless electronic module. 1. Introduction The fiber Bragg grating (FBG) sensing technology has been exten- sively investigated by the scientific community in recent decades. It provides unique advantages such as immunity to electromagnetic in- terference, multiplexing and embedment capability. The FBG sensors have been widely applied in the field of structural health monitoring for metal, composite and concrete structures [1–5]. The FBG sensors are adopted for long-term strain monitoring by the construction indus- try [6,7] due to their well-known long-term reliability. They can also be used as temperature sensor and pressure sensor with high measurement repeatability and accuracy [8,9], as well as corrosion monitoring sensor [10,11]. However, the commercial FBG demodulation systems are generally expensive and bulky, which considerably limits the practical applica- tions (out of laboratory) of the FBG sensors. These FBG interrogators can interrogate several FBG sensors in multiplexing. There are two main types of multiplexing methods; time division multiplexing (TDM) and wavelength division multiplexing (WDM). The number of FBG sensors in TDM are limited as the sensors are of the same reflection wavelength and low reflectivity. The WDM method is widely used in commercial systems. The commercial WDM systems generally have one of the two configurations; (i) a broadband light source (very often super lumines- cent diode (SLD)) with a wavelength swept detector, or (ii) a wavelength swept laser (or tuneable laser) with a broadband detector [22–24]. Al- ∗ Corresponding author at: School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. E-mail address: cywyang@ntu.edu.sg (Y. Yang). though several FBG sensors can be multiplexed, the cost and the power consumption of all the electro-optic components in the commercial FBG interrogation system are still too high for field deployment. At a site, if FBG sensors are installed in low volume, at least one commercial in- terrogator need be deployed, which makes low volume FBG sensor in- stallation costly. In addition, laying fiber cables to take optical signals from all the FBG sensors to the interrogator is highly undesirable at construction sites. Managing fiber cables in a large sensor network is difficult and there is a high risk of data loss due to fiber breakage which may be caused by construction activities. Although a range of coatings and jackets is available to ruggedize the fiber, they further increase the cost. Moreover, the construction sites may have the presence of strong electromagnetic fields (because of strong motors and generators) which makes FBG sensor a preferable choice. Thus, there is a great need for robust and standalone FBG sensors with minimum fiber cable layout and wireless communication (preferably) in many civil and geotechni- cal monitoring applications. Several FBG interrogation designs have been proposed in the litera- ture. Matched-gratings (identical gratings) are used to track the wave- length change of the FBG sensors for strain measurement [12]. One of the identical gratings is mounted on a piezoelectric driven stretching device. This technique is complicated and dependent on the perfor- mance of the piezoelectric transducer. Moreover, the strain measure- ment range is limited to ±200 . Another reported FBG interroga- tion method is a tunable Fabry–Perot filter mounted on a piezoelec- https://doi.org/10.1016/j.optlaseng.2019.05.025 Received 1 February 2019; Received in revised form 22 May 2019; Accepted 23 May 2019 0143-8166/© 2019 Elsevier Ltd. All rights reserved.