JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 24, DECEMBER 15, 2009 5675 Metallic-Grating-Based Interconnector Between Surface Plasmon Polariton Waveguides Dawoon Choi, Il-Min Lee, Jaehoon Jung, Junghyun Park, Jae-Hoon Han, and Byoungho Lee, Senior Member, IEEE Abstract—A metallic-grating-based interconnection scheme that interconnects two waveguide layers of surface plasmon polaritons (SPPs) is presented. We designed a diffraction grating for radiating light from the SPPs into free space or a homogeneous medium. An efficient receiver grating for receiving the light into SPPs is also explored. Using the well-established finite-element method, the ap- propriate grating geometry parameters are found. The directional interconnection efficiency is 32.4% for the best case in our numer- ical analysis. Index Terms—Metallic grating, optical interconnection, plas- monics, surface plasmon polaritons (SPPs). I. INTRODUCTION D ue to remarkable developments of the electronic technolo- gies, low power consumption, fast operation speed, and miniaturization have been the tendency of electronic devices. While the significant improvements are still in progress, it seems not to be taken before long to meet the uppermost RC time limit in miniaturization of the electronic devices [1]. Surface plasmon polaritons (SPPs) are electromagnetic waves that propagate along an interface between the metal and the dielectric [2]. Contrary to the light in nature, SPPs can propagate through the waveguides of subwavelength scales in transversal dimensions. With this property of SPPs that over- come the diffraction limit of light, SPPs are one of alternatives to realize both the much smaller device scale and faster infor- mation-processing speed, and have been widely researched in theoretical and experimental aspects [3]–[7]. Especially, in field of the ICs, it is surely predictable that more demands on the interconnections among the circuit layers or chips will be raised to increase the integration density. Elec- trical interconnections cannot perfectly solve electrical prob- lems such as clock skew, wavefront degradation, and crosstalk [8]. This is because, the access time between the memory and the processing unit becomes worse with higher level of integra- tion. Therefore, optical interconnection has been widely con- sidered as a method of the data communications in chip-to- Manuscript received May 30, 2009; revised August 24, 2009. First published October 06, 2009; current version published November 25, 2009. D. Choi, I.-M. Lee, J. Park, and B. Lee are with the National Creative Re- search Center for Active Plasmonics Applications Systems, Inter-University Semiconductor Research Center and School of Electrical Engineering, Seoul National University, Seoul 151-744, Korea (e-mail: byoungho@snu.ac.kr). J. Jung is with the School of Electrical, Electronics and Computer Engi- neering, Dankook University, Seoul 140-714, Korea. J.-H. Han was with the National Creative Research Center for Active Plas- monics Applications Systems, Inter-University Semiconductor Research Center and School of Electrical Engineering, Seoul National University, Seoul 151-744, Korea. He is now with the Woori Bank, Seoul 100–792, Korea. Digital Object Identifier 10.1109/JLT.2009.2033719 Fig. 1. Four types of interconnection method: (a) PF, (b) NF, (c) NB, and (d) PB interconnections. chip or board-to-board scale. Especially, in the optical ICs, the 3-D interconnections will permit the data communications in the raised integration density [8]. Recently, components of the ICs based on SPPs such as couplers [9], waveguides [7], and switches [10] have been researched. In addition, several inter- connection methods using SPPs have been devised, including dielectric slab [11], photonic crystal [12], and dielectric diffrac- tion grating [13]. In this paper, we investigate and suggest several configu- rations of the metallic-grating-based layer-to-layer intercon- necting methods. These can be categorized into four types de- pending on the directions of energy streams as in Fig. 1(a)–(d), which are named as positive-forward (PF), negative-forward (NF), negative-backward (NB), and positive-backward (PB), respectively. For each type, several parameters, such as the grating period, the grating height, and the offset distance between gratings (defined in Section II) are examined to im- plement an efficient interconnection, which naturally provides a guide for design procedures. II. INTERACTION OF THE SPPS WITH A DIFFRACTION GRATING STRUCTURE When -polarized and phase-matched light is incident on a metal–dielectric interface, SPPs can be excited. SPPs are highly confined near the interface and exponentially decaying in direc- tion perpendicular to the interface. From appropriate boundary conditions, the dispersion relation for the SPPs on an interface between half-infinite metal with electric permittivity and half-infinite dielectric with is given as [2] (1) 0733-8724/$26.00 © 2009 IEEE