Research On Sensing Properties Of Photonic Crystal Fiber Grating

Fiber grating is one of the most important optical passive components. By creating a periodic refractive index distribution structure in the fiber core, the spread behavior of light through the fiber can be controled by the fiber grating. The unique nature of the fiber Bragg grating can be used in the field of optical communication and optical sensing. Recently, the emergence and development of photonic crystal fiber (PCF) provides a new platform for the fiber grating. The effective refractive index of the transmission mode can be adjusted by the air hole layers, air filling factor and core diameter of PCF, then the spectral characteristics of the photonic crystal fiber grating (PCFG) can be controled, these novel characteristics of PCFG can be applied widely. The multi-peak structure and high senstivity of PCFG have shown great potential in the high-precision, multi-parameter and distributed sensing applications.The fundamental properties of PCFG are investigated and the sensing properties of PCFG are discussed theoretically. Firstly, the theoretical research model is established which based on coupled mode theory and effective index method of PCF. And then the spectrum of PCFG is simulated by the transfer matrix method, and the spectrum of PCFG influenced by the structural parameters of PCF and grating is analyzed. According to the resonance conditions of PCFG, the sensing characteristics of temperature and stress are simulated, and the relationship between structural parameters and sensitivity is analyzed. The results show that: the resonant wavelength and reflectivity are influenced by the structural parameters, the temperature and stress sensitivity coefficient are increased with the air filling factor and decreased with the core diameter. Finally, a double-parameter sensor is proposed on the basis of photonic crystal fiber long period grating, which temperature and stress can be sensed at the same time, the temperature and stress sensitivity coefficient of double-resonance are 1.93nm/℃,3.56nm/℃,0.0054nm/με,0.0058nm/μεrespectively.