长周期光纤光栅的折射率敏感特性

摘要

The sensitivity of long-period grating in refractive index sensing was analyzed by using the coupled-mode theory, and the formula of resonance wavelength shifts of LPFGs which changes relative to the surrounding refractive index was derived. If the period of grating is not changed, when the cladding refractive index is less than and close to the surrounding refractive index, the results show that the resonant wavelength shifts increased. The resonant wavelength shifts are greater for higher order cladding modes and smaller fiber cladding radius and smaller cladding refractive index, namely, the sensitivity to the surrounding refractive index is obviously enhanced. When the surrounding refractive index is greater than the fiber cladding refractive index, the resonant wavelength of grating will remain unchanged.%利用光波导的耦合模理论分析了长周期光纤光栅(LPFG)的折射率传感特性,给出了LPFG 的谐振波长相对于环境折射率变化时的漂移量解析表达式.对 LPFG 的折射率传感特性进行了数值模拟.结果表明:在光栅周期不变的情况下,当包层折射率小于且接近外界环境折射率时,波长的漂移量增大,且对应的模次越高、包层半径越小、包层折射率越小,波长漂移量越大,即 LPFG 对应于外界折射率传感灵敏度得到显著提高;当外界环境折射率大于包层折射率时,光栅的谐振波长将近似不变.