Photonic differentiators can implement the differentiation of ultrafast optical signals in optical domain directly without electronic processing. Photonic differentiation (DIFF) is attracting lots of interests due to its potential wide applications in the optical digital processing and analog processing. Currently, arbitrary-order photonic differentiators are widely studied since the differentiated signals have a variety of temporal waveforms. An Nth-order optical temporal differentiator is defined as a device that provides the Nth-time derivative of the complex envelope of an input optical signal. Most of the schemes were reported using specially designed fiber Bragg gratings, which are in fact fiber optics technologies or bulky systems. However, photonic DIFF with silicon-based waveguides, can offer distinct advantages of increased stability and reliability, compactness, capability of integration with electronics.
Several researchers in Wuhan National Lab for Optoelectronics, including Prof. Xinliang Zhang, Prof. Jianji Dong, Prof. Dingshan Gao and Mr. Aoling Zheng, etc have experimentally demonstrated high-order photonic differentiators using an on-chip cascaded microring resonators. These microring resonators are designed with near critical coupling condition to meet the differentiator requirements. The first-, second- and third-order DIFFs are demonstrated using one single microring unit, two cascaded microring units, and three cascaded microring units, respectively. For a periodical Gaussian optical pulse injection, the average deviations of all differentiators are less than 6.2%. The differentiation of pseudo random bit sequence (PRBS) signals at 5Gbit/s is also demonstrated.
This work was published in Optics Letters (vol. 38, pp. 628–630, 2013), and was orally presented on the OFC/NFOEC 2013, Anaheim, CA, US. Relative work was partially supported by the National Basic Research Program of China (Grant No. 2011CB301704), the Program for New Century Excellent Talents in Ministry of Education of China (Grant No. NCET-11-0168), and the National Natural Science Foundation of China (Grant No. 60901006, and Grant No. 11174096).
Fig. 1. Fabricated silicon microring resonators.
Fig. 2 Experimental results for high order DIFF waveforms.