JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 28, NO. 24, DECEMBER 15, 2010 3569 On-Chip Wireless Optical Broadcast Interconnection Network Hongyu Zhou, Student Member, IEEE, Zheng Li, Student Member, IEEE, Li Shang, Member, IEEE, Alan Mickelson, Senior Member, IEEE, and Dejan S. Filipovic, Senior Member, IEEE Abstract—An on-chip wireless optical broadcast network for fu- ture multicore CPU interconnections is introduced in this paper. A baseline topology is composed of 32 identical transmitting/re- ceiving optical dielectric rod antennas arranged around a circular ring. To ensure balanced power distribution between the chan- nels, the optical antenna design was governed by the antennas’ far-field radiation pattern and near-field coupling. Over the fre- quency range of 172 THz (1750 nm) and 222 THz (1350 nm), the broadcasting network has average and minimum transmissions of and dB, respectively. The overall transmission effi- ciency is maintained above 70% throughout the operating band- width. Results are confirmed by the full-wave simulations based on finite integration and finite element methods. For additional vali- dation, an eight-channel microwave broadcasting network is fab- ricated, and excellent agreement between the full-wave design and measurements are obtained. Index Terms—Multicore interconnection, on-chip broadcast, op- tical antenna, silicon-on-insulator (SOI) wafer, silicon photonics. I. INTRODUCTION C ONTINUOUS advances in fabrication technologies have contributed to the reduced size, improved performance, and enhanced power efficiency of transistors. However, metallic wires, the main interconnect solution in ICs, do not scale at the same pace. As a result, on-chip communication has become a key challenge for emerging multicore and multibillion-tran- sistor ICs. The fundamental physical limitations of electrical interconnects include communication throughput, latency, and power dissipation. For instance, the power consumption of electrical interconnections may exceed the projected on-chip IC communication power budget by over a factor of ten for future technology generations [1]. Recent advances in silicon photonics have enabled promising alternatives for future on-chip interconnections [2]. Based on optical silicon waveguides, various on-chip photonic network designs, including bus, ring, Mesh and Clos network, have Manuscript received June 15, 2010; revised September 14, 2010; accepted October 29, 2010. Date of publication November 09, 2010; date of current ver- sion December 08, 2010. This work was supported by the National Science Foundation under Grant CCF-0829950 “EMT/NANO: Broadcast Optical Inter- connects for Global Communication in Many-Core Chip-Multiprocessor.” The authors are with the Department of Electrical, Computer, and Energy Engineering, University of Colorado at Boulder, Boulder, CO 80309 USA (e-mail: Hongyu.Zhou@colorado.edu; Zheng.Li@ colorado.edu; Li.Shang@colorado.edu; Alan.Mickelson@colorado.edu; Dejan@colorado.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org Digital Object Identifier 10.1109/JLT.2010.2091105 been proposed to facilitate efficient on-chip communication for future many-core ICs. However, there are challenges that these optical interconnects have yet to overcome. Particularly, in many-core systems, a vital part of the on-chip traffic are short, often-multicast, and latency-critical messages. They are employed to synchronize concurrent program threads execu- tion, maintain distributed on-chip data coherence, and manage global resources. If these messages are not properly handled, the many-core IC system performance degrades substantially [3]. Therefore, a power efficient, low-latency, and high-band- width optical broadcast communication solution is crucial for providing instant global reach for the performance-critical, multidestination on-chip traffic. Foreseeing these challenges, different photonic broadcast communication topologies have been proposed. For example, an N M multimode interference (MMI) network [4 ] based on the self-imaging theory and equal splitting of the input signal into multiple outputs has been successfully demonstrated. While characterized by small loss and excellent output balance, the MMI network’s bandwidth is inversely proportional to the count of input and output ports [5]. It is shown that 1 32 MMI exhibits a 7 nm bandwidth for 1550 nm operating wavelength [6]. This inherent property strongly restricts MMI for on-chip broadcast applications where broadband wavelength-division multiplexing (WDM) support is needed. Therefore, new solu- tions are needed for future many-core on-chip communication. In this paper, we introduce a wireless optical broadcast inter- connection network (WOBIN) as a viable candidate for future multicore IC on-chip communications. Wireless channels are linked by multiple identical optical dielectric rod antennas com- pactly arranged around a circular ring. Antennas are designed and laid out such that the near-field coupling and far-field ra- diation provide the best power balance between the channels. The designed WOBIN has 50 THz (400 nm) bandwidth, thereby providing sufficient bandwidth support for on-chip WDM com- munication. Specifically, from 172 THz (1750 nm) to 222 THz (1350 nm), the designed 32-channel WOBIN can split the input power from any chosen channel to the 31 remaining channels with good power balance. The average output is dBm per channel for 0 dBm input power. Minimum channel output is maintained above dBm, while the overall transmission efficiency is between 70% and 80% (0.97–1.55 dB total device loss). Based on the recently published literature and the loss budget analysis of future multicore ICs, the designed 32-channel WOBIN WDM solution requires a total power budget of only 29.5 mW for on-chip communication. This topology is orders of magnitude more efficient than corresponding electrical on-chip communication solutions. 0733-8724/$26.00 © 2010 IEEE