Strain and temperature rcsponses of ilic FBG sciisor were IIICRStired sepiralcly. The temperature was scl by using ii temperalui-c CoiitroIIcr and strain WBS applied hy using a micrometer-driven stage. The FUG sensor was addressed using ii light cmitting diode and tlic reflection spcctrum was monitored by an optical spectrum analyser. During the strain rcsponse mc;isurcrnenl, the tcmperaturc was kept at 22°C lo avoid c m r s rcsulting Roin tcinpcratnrc variations. Fig. 3 shows thc response of

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... e two Uragg wavclcnglhs l o slrain ;ipplied to the sciisor. The two wavelcngtlis s h o w similar strain responses; the vducs ofk" and Ite2 wcre estimiilcd l o bc 1.05 and I . O 4 p m /~, respcctivcly, as expected. Fig. 4 shuws ilie experimental rcsults Cor tciiipcrature rcspoiise imeasurcment whilc the FRG sensor was held unstraincd. The values of kT1 and ICy2 were eslirnalcd to he 10.6 and 9.2pmi"C, respectively. Er/Yh dop ing leads to a decrease in the thermo-optic coefficient of ilic fibre so that the tempcrature coeflicient of lhe grntiiig section in llie Er/ Yh-doped fibrc is less than that in Coming SMI:-28 fibi-c, ELECTRONICS LETTERS 8th June 2000 No,