KSME International Journal, VoL 15, No.3, pp. 309-319, 2001 309 Planar Optical Waveguide Temperature Sensor Based on Etched Bragg Gratings Considering Nonlinear Thermo-optic Effect Sang-Mae Lee Center for Microelectronic Sensors and MEMS, Department of Electrical & Computer Engineering and Computer Science, University of Cincinnati Kook.-Chan Ahn"" Department of Mechanical Design Engineering, Chinju National University Jim S. Sirkis Smart Materials and Structures Research Center, Department of Mechanical Engineering, University of Maryland This paper demonstrates the development of optical temperature sensor based on the etched silica-based planar waveguide Bragg grating. Topics include design and fabrication of the etched planar waveguide Bragg grating optical temperature sensor. The typical bandwidth and reflectivity of the surface etched grating has been -0.2 nm and -9 %, respectively, at a wavelength of -1552 nm. The temperature-induced wavelength change is found to be slightly non-linear over -2oo·C temperature range. Typically, the temperature-induced fractional Bragg wavelength shift measured in this experiment is 0.0132 nmj"C with linear curve fit. Theoretical models with nonlinear temperature effect for the grating response based on waveguide and plate deformation theories agree with experiments to within acceptable tolerance. Key Words: Etched Bragg Grating, Planar Light Waveguide, Butt Coupling Technique, Nonlinear Thermooptic Effect, Temperature Sensor, Classical Lamination Theory 1. Introduction High-temperature strain measurements are crit- ical to understanding constitutive properties of new high-temperature materials such as metal matrix composites (MMCs), ceramic matrix com- posites (CMCs), and carbon/carbon composites (CCCs), as well as for determining the mechani- cal reliability of components produced from these materials. These materials are finding greater use in applications involving advanced aeropropul- t First Author • Corresponding Author, t-mail: kcahn@chinju.ac.kr TEL; +82-591-751-3352; FAX; +82-591-751-3359 Department of Mechanical Design Engineering, Chinju National University, 150Chilam-dong, Chinju, Kyun- gnam 660-758, Korea. (Manuscript Recevied June 21, 2000; Revised December 21, 2000) sion systems and high speed civil transport. Strain gages most commonly used in high temperature measurements are resistance based foil strain gages (Wu et al., 1981 ; Hudson, 1989 ; Stange, 1983 ; Lei et al., 1989) or capacitance based strain gages (Harting, 1975 ; Noltingk, 1974 ; Norris and Yeakley, 1976) and are all limited operating temperature of less than -850 ·C. The recent entry in high temperature strain sensing field are transducers based on cylindrical optical waveguides (optical fibers) produced from amor- phous silica (Chang et al., 1994; Lee and Taylor, 1991) and sapphire (Dils, 1983 ; Wang et al., 1992). Silica based optical fiber sensors have been demonstrated up to 1200 ·C, while sapphire- based sensors have been demonstrated in tempera- ture regimes near 17oo·C. While sapphire sensors are attractive for high temperature sensor applica- tions, they face a number of technical challenges. Optical grade sapphire fibers are difficult and