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镀膜长周期光纤光栅(LPFG)工作于相位匹配转折点时纤芯模与高次包层模的耦合产生单个宽带损耗峰,其3 dB带宽取决于纤芯模和包层模之间的色散差、光栅长度以及中心波长.研究表明,薄膜折射率和厚度的变化将影响纤芯模与包层模之间的色散差,从而影响损耗峰的3 dB带宽,同时损耗峰中心波长亦随之移动.薄膜折射率为1.57,厚度为350 nm时,损耗峰带宽可达302 nm.减小光栅长度在保证中心波长损耗大于6 dB的前提下可使损耗峰3 dB带宽增大至334 nm.进一步研究表明,在均匀LPFG中偏离光栅中点的适当位置引入单个π相移可以使带宽增大至372 nm以上.
The coupling of the core mode with the high-order cladding mode produces a single broadband loss peak when the coated long-period fiber grating (LPFG) operates at the phase-matching inflection point with a 3 dB bandwidth that is dependent on the dispersion difference between the core and cladding modes, Grating length and center wavelength.Research shows that the change of film refractive index and thickness will affect the dispersion difference between core mode and cladding mode and affect the 3 dB bandwidth of loss peak and the center wavelength of loss peak. When the refractive index of the film is 1.57 and the thickness is 350 nm, the bandwidth of the loss peak can reach 302 nm. Reducing the length of the grating can increase the 3 dB bandwidth of the loss peak to 334 nm while ensuring that the central wavelength loss is greater than 6 dB.Further study It is shown that the introduction of a single π-phase shift at an appropriate position in the uniform LPFG that deviates from the mid-point of the grating can increase the bandwidth above 372 nm.