长周期光纤光栅分数阶全光微分器研究

Photonic temporal differentiator is an import device in the all-optical signal processing system, and it has become a hot topic of research. In this paper, we investigate photonic temporal differentiator based on a long-period fiber grating, which has broad bandwidth compared to the differentiator using a fiber Bragg grating. We study the mechanism of transmission and design the structure of the long-period fiber grating, and propose the innovation schemes for achieving the fractional-order differentiation by changing the coupling state between the core mode and the cladding mode. The effects of signal pulse width and duty ratio are also investigated. For picosecond Gaussian pulse, the fractional-order differentiation is demonstrated, and the cross-correlation coefficient between the ideal output and the the actual output is 90.2% for the first-order differentiation. Comparing with the ideal differential results, the cross-correlation coefficients are respectively 91.3% and 88.4% when the fractional order is at 0.7 and 1.2.