With the rapid development of data centers and high performance computers, silicon photonics has grown as an ideal solution for high-bandwidth on-chip interconnects and energy-efficient telecommunications. On-chip short-reach communication and computing with silicon waveguides become very important, where very basic optical processors, such as optical differentiators, integrators, and logic units, are highly desirable. A temporal photonic differentiator (DIFF) is a basic operator that performs real-time DIFF of the field envelope of an optical signal. Photonic DIFF can be categorized with integer-order DIFF and fractional-order DIFF. Fractional-order DIFF is the extension of integer-order DIFF, which can accomplish what integer-order differentiation cannot do. Currently, the fractional-order DIFF has been implemented with different methods such as asymmetrical phase-shifted fiber Bragg grating, tilted fiber Bragg grating, silicon-on-isolator (SOI) MRR with a multimode interferometer (MMI) coupler, and electrically tuned Mach–Zenhder interferometer (MZI).
Several researchers in Wuhan National Lab for Optoelectronics, including Prof. Xinliang Zhang, Prof. Jianji Dong, and Master student Aoling Zheng, have experimentally demonstrateda tunable fractionalorder photonic differentiator using an on-chip electrically tuned microring resonator structure. When different voltages are applied on the MRR, the carrier in thering waveguide is changed to vary the internal refractiveindex and loss, which leads to the change of Q-factor andphase shift at resonant frequencies. Thus, a fractional order DIFF can be implemented. The proposed DIFF isexpected to have an operation bandwidth of tens ofgigahertz and have high energetic efficiency. It was demonstrated that the fractional order of a Gaussian pulsewith a pulse width of 30 ps and a rectangular pulse witha pulse width of 70 ps could be tuned from 0.58 to 0.97and 0.63 to 0.97, respectively.
This work has been published in Optics Letters (Vol. 39, No. 21, pp. 6355-6358, 2014). Relative work was partially supported by the NationalNatural Science Foundation of China (GrantNo. 61475052, Grant No. 11174096), National Basic Research Program of China (Grant No. 2011CB301704), Program for New Century Excellent Talents in Ministry of Education of China (Grant No. NCET-11-0168),and the Foundation for the Author of National ExcellentDoctoral Dissertation of China (Grant No. 201139).Full text can be viewed by
A. Zheng, J. Dong, L. Zhou, X. Xiao, Q. Yang, X. Zhang, and J. Chen, "Fractional-order photonic differentiator using an on-chip microring resonator," Opt. Lett. 39, 6355-6358 (2014).
Fig.1 (a) Microscope image of the fabricated MRI and (b) microscope image of the zoom-in ring region.
Fig. 2. (a) Input Gaussian pulse with an FWHM of 30 ps, and the differentiated pulses at the different voltages corresponding to differentiation orders of (b) N=0.97, (c) N=0.80, (d)N=0.63, and (e) N=0.58.
Fig. 3. (a) Input rectangular pulse with an FWHM of 70 ps, andthe differentiated pulses at the different voltages correspondingto differentiation orders of (b) N=0.97, (c) N=0.80, and(d)N=0.63.