基于多模干涉理论和长周期光纤光栅(LPFG)的传感特性，提出了一种单模多模单模(SMS)结构与LPFG级联的光纤传感器，实现了温度和折射率的同时测量。实验结果表明，SMS结构的干涉谱和LPFG对温度和折射率具有不同响应灵敏度，其温度灵敏度分别为0.017 nm/℃和0.060 nm/℃；SMS结构对折射率不敏感，而LPFG的折射率灵敏度为-35.60 nm/RIU(RIU为折射率单位)。因此利用敏感矩阵，实现对温度和折射率的同时测量，得到温度和折射率的最大测量误差分别为±0.59 ℃和±0.0013。该结构灵敏度高、结构简单，且不易受电磁等干扰。实验结果具有良好的线性度，在生物化学领域应用前景良好。

Based on the multimode interference theory and the sensing characteristics of long-period fiber grating (LPFG), a fiber-optic sensor composed of a single mode fiber (SMF)-multimode fiber (MMF)-SMF (SMS) structure and a LPFG is proposed for simultaneous measurement of temperature and refractive index. The experimental results show that the interference spectrum of SMS structure and LPFG have different response sensitivities to temperature and refraction index, and the temperature sensitivity coefficients are 0.017 nm/℃ and 0.060 nm/℃, respectively. The SMS structure is insensitive to refractive index while the refractive index sensitivity coefficient of LPFG is -35.60 nm/RIU. Using the sensitivity matrix, simultaneous measurement of temperature and refractive index is realized. The maximum measurement errors of temperature and refraction index are ±0.59 ℃ and ±0.0013, respectively. With the advantages of high sensitivity, simple structure, immunity to electromagnetic interferences and good linearity, the structure has a excellent application prospect in biochemistry field.