Waveguide-coupled parallel optical transceiver technology for Tb/s-class chip-to-chip data transmission Fuad E. Doany* a , Clint L. Schow a , Jeffrey A. Kash a , Christian Baks a , Russell Budd a , Daniel M. Kuchta a , Petar Pepeljugoski a , Frank Libsch a , Roger Dangel b , Folkert Horst b , Bert J. Offrein b a IBM – T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, 10598; b IBM Research GmbH, Zurich, Switzerland ABSTRACT The IBM Terabus program has developed parallel optical interconnects for terabit/sec-class chip-to-chip communications through printed circuit boards with integrated optical waveguides. 16 TX + 16 RX channel transceiver “Optomodules” were assembled and fully characterized, with fiber-coupled full links operating up to 15 Gb/s, for an aggregate bi-directional data transfer rate of 240 Gb/s. Furthermore, we have demonstrated a complete link between two Optomodules through polymer waveguides on a printed circuit board, with all 32 uni-directional links operating error- free at 10Gb/s, for a 160 Gb/s bidirectional aggregate data rate. This is the fastest, widest, and most integrated multimode optical bus ever demonstrated. Keywords: Optical interconnects, parallel optical links, optical transceivers 1. INTRODUCTION The steadily increasing demand for higher bandwidth interconnects in high performance computing systems is progressively more difficult to meet using electrical interconnect technology. Today, optical interconnects are commonly used for the longer (>10m) high speed links and are increasingly replacing electrical links at shorter distances. Furthermore, advanced high performance chips and multi-chip modules are increasingly limited by their off- chip or off-module bandwidth. [1] Board-level optical data buses offer the potential alleviate this I/O bottleneck by providing dense, parallel high speed data links. In the Terabus program, we are developing parallel optical interconnects for terabit/sec-class chip-to-chip and module- to-module communications through printed circuit boards with integrated optical waveguides. [2,3] The data links are enabled by parallel transceiver modules, or “Optomodules,” that incorporate key technologies including: high-speed, low-power CMOS analog amplifier circuits; efficient, high-speed 985 nm substrate illuminated/emitting photodiode (PD) and VCSEL arrays with integrated collimating lenses; and the extensive use of flip-chip packaging to minimize the module dimensions and associated packaging parasitics. The core of the module is a novel “Optochip”: a 5.25 mm x 3.25 mm single-chip CMOS optical transceiver IC with flip-chip attached 4 x 4 VCSEL and PD arrays. The Optochip is then flip-chip attached to a high-density organic package to form the Optomodule. A conventional ball grid array (BGA) solder process is then used to mount this low-cost, low-profile package on a printed circuit board with integrated optical waveguides (“Optocard”). Polymer waveguides on a 62.5-µm pitch are incorporated in the FR4-based Optocard. Optical and electrical connections are simultaneously established during the Optomodule-to-Optocard attachment. 2. COMPONENTS AND ASSEMBLY The Terabus transceiver optical link is schematically depicted in Figure 1. The link consists of two Optomodules interconnected through the waveguides on Optocard. The fundamental component of the Optomodule is the transceiver Optochip, a CMOS IC with flip-chip attached optoelectronic devices. The Optochip is in turn flip-chip attached to the organic SLC carrier, forming the complete Optomodule. A detailed description of the components is provided below. *doany@us.ibm.com; phone 1 914 945-2831; fax 1 914 945-4219 Invited Paper Photonics Packaging, Integration, and Interconnects VIII, edited by Alexei L. Glebov, Ray T. Chen Proc. of SPIE Vol. 6899, 68990V, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.763670 Proc. of SPIE Vol. 6899 68990V-1 2008 SPIE Digital Library -- Subscriber Archive Copy