【Research Progress】 All-optical temporal differentiation

Release time:2016-01-31 22:58

Optical signal processing like differentiation or integration usually needs to convert optical signals into electrical signals, and then use digital circuits or analog circuit for electronic signal processing, finally convert back to optical signals. However, with increasing bandwidth of an optical signal, a photoelectric conversion bandwidth is limited in signal processing. Therefore all-optical signal processing devices can overcome the electronic bottleneck.

The photonic temporal differentiator (DIFF) is one of the equivalent fundamental devices that forms the basic building blocks in electronics. It provides the time derivative of the complex envelope of an arbitrary input optical waveform, which has wide applications in ultra-fast signal generation, ultrahigh-speed coding and pulse shaping. Device operation bandwidth is one of main performance parameters of a differentiator, and we have found that in evaluating the processing-speed performance of differentiators one should also consider the minimum operation bandwidth that can be processed with a prescribed accuracy. However, maximum operation bandwidth is the figure of merit that researchers preferred. The largest operation bandwidth of 25-THz is provided by a compact all-fiber wavelength selective directional coupler. However the largest operation bandwidth of the differentiators based on silicon-on-insulator is about 500-GHz. So how to design a terahertz-bandwidth photonic temporal differentiator based on the silicon device is a problem to solve.

Directional couplers can be produced in fiber or integrated waveguide platforms, and can silicon directional couplers provide the large operation bandwidth? With this query, Prof. Xinliang Zhang, Prof. Jianji Dong and Master Tianli Huang have made a theory analysis and the experimental verification. They simulated the amplitude response and phase response of the silicon directional couplers, analyzed the feature of a large operation bandwidth device provided, and achieved an experiment implementing the first-order differentiation. The performance of this photonic differentiator is tested using Gaussian-like pulses with a pulse width of 2.8 ps, 4 ps, 6 ps, 8 ps, and 10 ps, respectively. The differentiation processing errors and relative energy efficiency are also discussed. They implemented the first differentiator with an operation bandwidth of 1.25 THz. This silicon chip may have potential applications in integrated photonic computing circuits with sub-picosecond pulses.

This research result is published on the Journal of Optics Letters (Vol.40.No.23.pp.5614-5617.2015). This work is supported by Foundation for the Author of National Excellent Doctoral Dissertation of the People’s Republic of China (FANEDD) (201139), National Basic Research Program of China (2011CB301704), National Natural Science Foundation of China (NSFC) (11174096, 61475052), Opened Fund of the State Key Laboratory on Advanced Optical Communication System and Network (2015GZKF03004) and Program for New Century Excellent Talents in Ministry of Education of China (NCET-11-0168).