As a crucial building block of the photonic integrated circuit (PIC), a photonicdifferentiator (DIFF) plays one of the key roles in analogoptical signal processing due to its functionality of performingtemporal differentiation of optical signal waveforms. SiliconPICs have been proposed to perform photonic differentiationby utilizing micro-ring resonators,Mach–Zehnder interferometers, and directional couplers.An ultra-wide-bandwidth DIFF has long beenpursued by the scientific community due to its ability to process ultra-high-speed optical signals. However, presentDIFFs have lower limitations of the operation bandwidthsdue to the energy efficiency of the DIFF. This fact indicates that even a photonic DIFF with terahertz operation bandwidth remains to be a bandpass device because it cannot process a low speed signal. This study led by Prof. Jianji Dong has been published on the Optics Express in 2015 (Opt. Express,23, 18925-18936, 2015).
Figure1: Schematic of the PhCW-MZI
To address this issue, Prof.Dong proposed a novel scheme based on photonic crystal waveguide (PhCW). By optimizing the structural parameters of the photonic crystal waveguide, the slow-light effect is obtained. Two PhCWshaving different lengths and placed in separate arms of a MZIstructure as Fig. 1 shows.As the slow light effect is related to the wavelength, a wavelength-dependable transmission spectrum can be obtained as Fig. 2 indicates, demonstrating the possibility of PhCW-MZI to act as a photonic differentiator.
Figure 2: Transmission spectrum of the PhCW-MZI.
Based on this theoretical model, Prof. Dong’s team cooperated with Dr. Yunhong Ding’s team to fabricate the device. Opticalpulses with pulse widths ranging from 2.7 to 81.4 ps have beendifferentiated with process accuracy higher than 87.5%, according to our experimental results. The proposed conceptcan effectively avoid the bandwidth limitation of the photonicDIFF; hence, it will greatly enhance the performance of photonic DIFFs and largely expand the application field of DIFFsin large-scale photonic computing circuits, as well as inintegrated optical signal processing systems.
Figure 3:Experimental results.
On the 11thApril, 2017, this work is published on the Optics Letters. This work is supported by National Natural Science Foundation of China(NSFC) (61475052, 61622502); Opened Fund of the StateKey Laboratory on Advanced Optical CommunicationSystem and Network (2015GZKF03004); Ministry ofEducation of the People’s Republic of China (MOE)(NCET-11-0168).
The link of the full-text article is：
https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-8-1596。
