Abstract: Two schemes of using a long period fiber grating(LPFG) for simultaneous discriminating measurement of temperature and refractive index are proposed.The schemes are based on the spectrum characteristics of the long period grating. The spectrum is composed of multiple and different loss peaks.The sensitivities of the peaks are different, and the logarithm of the light intensity in an approximate linear region near the resonant wavelength is linear when the temperature and refractive index change, so is the resonant wavelength.With detailed theory and numerical simulation,it proves the feasibility. The sensor with a long period grating is less sensitive than the other sensors with complex structure. It has good application prospect because of the simple demodulation,attractive price and smaller size.

Key words: long period fiber grating(LPFG), transmission spectrum, temperature sensing, refractive index sensing