Author:       2015-08-27

In addition to conventional advantages of reduced system size and dramatically lower cost, employing photons as information carriers also benefits from higher processing speed and lower power consumption. Great efforts have been paid to replace the traditional electronic computing circuit with integrated photonic circuit due to its tremendous potential in the future interconnection systems. As an indispensable computing block in all-optical computing, photonic field differentiator has long been a focus since it was first proposed. Until now, the photonic differentiation was implemented by lots of optoelectronic devices, including micro-ring resonators, Mach-Zehnder interferometers and directional couplers. To date, most reported photonic differentiators are chasing to boost the upper bandwidth limitation, beyond which the processing accuracy will decrease greatly. However, in the practical application of photonic differentiator, the minimum operation bandwidth should always exist, which is neglected by the scientific community.

Prof. Jianji Dong, Prof. Jinsong Xia and Prof. Xinliang Zhang of Wuhan National Laboratory for Optoelectronics for the first time proposed and theoretically analyzed operation bandwidth range with both upper and lower limitation. By introducing the noise model of photodetectors into our calculations, we infer that the photonic differentiator has the lower limitation of operation bandwidth. In addition, we fabricated three samples of silicon photonic crystal nano-cavities (PCNs) with different Q factors to verify our theoretical prediction. The results have great value in the theory and further application of the photonic differentiator.

This work is 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), a Foundation for Author of National Excellent Doctoral Dissertation of China (Grant No. 201139), the National Natural Science Foundation of China (Grant No. 11174096 and 61475052), the Major State Basic Research Development Program of China (Grant No. 2013CB632104 and 2013CB933303) and National Natural Science Foundation of China (Grant No. 61335002).

Fig. 1. Cross-correlation Coefficient calculation results with noise under different BW of the DIFF. (a) BW=50 GHz. (b) BW=100 GHz. (c) BW=250 GHz

Fig. 2. (a) Scanning electron microscope of the PCN. (b)-(d) Zoom in region of three different nano-cavities with different Q factors. (e)-(g) Measured transmission spectra of three PCNs, respectively.

Fig. 3. Time domain and spectrum measurement results of high speed DIFF. (a)-(d). Input temporal waveforms. (e)-(h): Output temporal waveforms. (i)-(l). Measured spectra.