Temporal photonic differentiator is a basic operator that performs real-time differentiation of the field envelope of an optical signal, which has wide applications in numerous fields such as pulse characterization, ultra-fast signal generation, and ultra-high-speed coding. Numerous techniques have been proposed recently to implement all-optical temporal differentiation, including the use of a long period fiber grating, a phase shifted fiber Bragg grating, an interferometer, a semiconductor optical amplifier, a silicon microring resonator or a directional coupler. In 2008, Cuadrado- Laborde et al explored fractional differentiation for the first time, and presented an all-optical temporal differentiator using a photonic Mach-Zehnder interferometer (MZI) by numerical simulations, but the tunability of the differentiation order was not mentioned. Fractional differentiation can be considered as a generalization of integer-order differentiation, with potentials to accomplish what integer-order differentiation cannot.
Several researchers in Wuhan National Lab for Optoelectronics, including Prof. Xinliang Zhang, Prof. Jianji Dong, Mr. Aoling Zheng etc have experimentally demonstrateda tunable fractionalorder photonic differentiator using an on-chip electrically tuned Mach-Zehnder interferometer (MZI) structure. The phase shift at the resonantfrequency of the MZI varies when applying different voltages, which canimplement the fractional differentiation. Due to the large 3-dB bandwidth ofthe MZI, the differentiator is expected to have an operation bandwidth ofseveral hundred GHz. A Gaussian-like pulse with a bandwidth ofabout 200 GHz is temporally differentiated with a tunable order range from0.83 to 1.03.To fulfil the chip-level optical processor, silicon-based waveguide is preferred, which can offer intrinsic advantages of compact footprint, well integration capability and compatibility with complementary metal-oxide semiconductor (CMOS) technology.
This work has been published in Optics Express(Vol. 22, No. 15,pp. 18232-18237, 2014). Relative work was partially supported by the National Natural Science Foundation of China(Grant No. 60901006, Grant No. 11174096), National Basic Research Program of China(Grant No. 2011CB301704), and the Program for New Century Excellent Talents in Ministryof Education of China (Grant No. NCET-11-0168), and the Fundamental ResearchFunds for the Central Universities, HUST: 2014YQ015.Full text can be viewed by
A. Zheng, T. Yang, X. Xiao, Q. Yang, X. Zhang, and J. Dong, "Tunable fractional-order differentiator using an electrically tuned silicon-on-isolator Mach-Zehnder interferometer," Optics Express, vol. 22, pp. 18232-18237, 2014.