Time-Domain Numerical Investigation of Ring Resonator Optical Delay Devices

As the demand for high-speed communication both in wired and in wireless systems increases, the optical fiber communication systems have been developed in such a way that the information transmission capacity through an optical fiber exceeds terabits per second. As the data speed increases, the packet switching network is expected to advance from electronic packet switching to all-optical packet switching networks in which electrical-to-optical and optical-to-electrical conversions are not involved. In the all-optical packet switching networks, optical packets carried in a specific wavelength channel can be routed to a destination transparently, thus the network can be expanded flexibly when necessary [1-2]. Furthermore, optical packet switching system might be adopted in optical interconnection technology for high-speed signal transmission as the VLSI (Very Large System Integration) circuits become extremely integrated [3]. In the all-optical packet switching or optical interconnection system, optical switches and variable optical delay modules are required. There have been a variety of approaches to realize optical delay modules [4-16]. A CROW (Coupled resonator optical waveguide) [5-8] has drawn interest for all-optical packet communication or optical signal processing modules because it can reduce the propagation speed variably. The CROW can be implemented in the form of Fabry-Perot, photonic crystal, or ring resonators, etc. Among them, the CROW based on ring resonators have shown noticeable advances in practical realization in terms of design and fabrication feasibility [7]. Even though several approaches in analytical and numerical analysis of the CROW’s provides lots of information regarding the delay performance of the devices [17-19], the quality of delayed pulse shapes can be directly investigated through a time-domain analysis. In this paper, an efficient split-step time-domain approach for the numerical analysis of the ring resonator devices such as CROW devices is presented [20-21]. The numerical algorithm is illustrated through the analysis of single-, double-, triple-, and quadruple-ring resonator all-pass filters, which can be extended to general CROW-type devices with arbitrary number of rings. In section II, the split-step time-domain algorithm is elaborated. In section III, the accuracy of the numerical approach is checked, and the delay characteristics of single-, double-, tripleand quadruplering all-pass filter (CROW device) are investigated and some design guidelines are presented. Finally, conclusions are given.