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In this paper, a laser-induced long-period fiber-grating (LPFG) optic sensor was packaged with a hybrid mechanism of elastic attachment and gauge length change for large strain measurements in a high-temperature environment. An emphasis was placed on the use of two cladding modes ( and ) of a single LPFG sensor for simultaneous strain and temperature evaluations so that exact temperature was used to compensate strain measurements. Both strain and temperature sensitivities of the LPFG sensor, as well as the strain transfer ratio due to a combined effect of elastic attachment and gauge length change, were analytically derived and validated with tension tests at elevated temperatures. The strain sensitivity of the LPFG sensor switched sign from negative for or lower modes to positive for or higher modes, whereas its temperature sensitivity remained positive. The sign switch for the …