Roger Dangel

Polymer-Waveguide-Based Board-Level Optical Interconnect Technology for Datacom Applications

On the basis of a realized 12times10 Gb/s card-to-card optical link demonstrator, the capabilities of a polymer-waveguide-based board-level optical interconnect technology are presented. The conception and realization of the modular building blocks required for this board-level optical interconnect technology are described in detail. In particular, we report on the fabrication and characterization of board-integrated optical low-loss polymer waveguides that are compatible with printed circuit board (PCB) manufacturing processes. We also explain our fully passive alignment technique, superseding time-consuming active positioning of components and connectors. To realize optical transceiver modules comprising vertical cavity surface emitting laser (VCSEL) arrays with laser drivers and photodetector arrays with transimpedance amplifiers (TIAs), a mass-production concept based on wafer-level processing has been elaborated and successfully implemented.

160 Gb/s Bidirectional Polymer-Waveguide Board-Level Optical Interconnects Using CMOS-Based Transceivers

We have developed parallel optical interconnect technologies designed to support terabit/s-class chip-to-chip data transfer through polymer waveguides integrated in printed circuit boards (PCBs). The board-level links represent a highly integrated packaging approach based on a novel parallel optical module, or Optomodule, with 16 transmitter and 16 receiver channels. Optomodules with 16 Tx+16 Rx channels have been assembled and fully characterized, with transmitters operating at data rates up to 20 Gb/s for a 27-1 PRBS pattern. Receivers characterized as fiber-coupled 16-channel transmitter-to-receiver links operated error-free up to 15 Gb/s, providing a 240 Gb/s aggregate bidirectional data rate. The low-profile Optomodule is directly surface mounted to a circuit board using convention ball grid array (BGA) solder process. Optical coupling to a dense array of polymer waveguides fabricated on the PCB is facilitated by turning mirrors and lens arrays integrated into the optical PCB. A complete optical link between two Optomodules interconnected through 32 polymer waveguides has been demonstrated with each unidirectional link operating at 10 Gb/s achieving a 160 Gb/s bidirectional data rate. The full module-to-module link provides the fastest, widest, and most integrated multimode optical bus demonstrated to date.

Chip-to-chip optical interconnects

Terabus is based on a silicon-carrier interposer on an organic card containing 48 polymer waveguides. We have demonstrated 4times12 arrays of low power optical transmitters and receivers, operating up to 20 Gb/s and 14 Gb/s per channel respectively

Terabit/s-Class Optical PCB Links Incorporating 360-Gb/s Bidirectional 850 nm Parallel Optical Transceivers

We report here on the design, fabrication, and characterization of highly integrated parallel optical transceivers designed for Tb/s-class module-to-module data transfer through polymer waveguides integrated into optical printed circuit boards (o-PCBs). The parallel optical transceiver is based on a through-silicon-via silicon carrier as the platform for integration of 24-channel vertical cavity surface-emitting laser and photodiode arrays with CMOS ICs. The Si carrier also includes optical vias (holes) for optical access to conventional surface-emitting 850 nm optoelectronic devices. The 48-channel 3-D transceiver optochips are flip-chip soldered to organic carriers to form transceiver optomodules. Fully functional optomodules with 24 transmitter + 24 receiver channels were assembled and characterized with transmitters operating up to 20 Gb/s/ch and receivers up to 15 Gb/s/ch. At 15 Gb/s, the 48-channel optomodules provide a bidirectional aggregate bandwidth of 360 Gb/s. In addition, o-PCBs have been developed using a 48-channel flex waveguide assembly attached to FR4 electronic boards. Incorporation of waveguide turning mirrors and lens arrays facilitates optical coupling to/from the o-PCB. Assembly of optomodules to the o-PCB using a ball grid array process provides both electrical and optical interconnections. An initial demonstration of the full module-to-module optical link achieved >; 20 bidirectional links at 10 Gb/s. At 15 Gb/s, operation at a bit error ratio of <; 10- 12 was demonstrated for 15 channels in each direction, realizing a record o-PCB link with a 225 Gb/s bidirectional aggregate data rate.

Polymer waveguides for electro-optical integration in data centers and high-performance computers.

To satisfy the intra- and inter-system bandwidth requirements of future data centers and high-performance computers, low-cost low-power high-throughput optical interconnects will become a key enabling technology. To tightly integrate optics with the computing hardware, particularly in the context of CMOS-compatible silicon photonics, optical printed circuit boards using polymer waveguides are considered as a formidable platform. IBM Research has already demonstrated the essential silicon photonics and interconnection building blocks. A remaining challenge is electro-optical packaging, i.e., the connection of the silicon photonics chips with the system. In this paper, we present a new single-mode polymer waveguide technology and a scalable method for building the optical interface between silicon photonics chips and single-mode polymer waveguides.

Development of a low-cost low-loss polymer waveguide technology for parallel optical interconnect applications

We report on the material evaluation, design, fabrication, and characterization of low-loss multimode polymer waveguides that are compatible with standard PCB manufacturing processes for use in large-area high-density high speed optical backplane interconnects.

Development of Versatile Polymer Waveguide Flex Technology for Use in Optical Interconnects

We report on the implementation of novel flexible polymer waveguide interconnects. They are based on newly developed mechanically flexible low-loss silicone waveguides. In addition to meeting the generic requirements of rigid waveguide interconnects, several flex-material challenges were mastered: a) mechanical flexibility permitting waveguide flexing down to radii of 1.0 mm without cracking; b) minimization of waveguide curling induced by the CTE mismatch between flex substrates and polymer layers to enable assembly and connectorization; c) greatly improved cladding adhesion on standard PCB flex substrates, such as polyimide; and d) high environmental stability despite the reduced polymer cross-linking required for better mechanical flexibility. The new waveguides exhibit excellent stability in damp heat (2000 h in 85°C/85% rH) and under thermal shock (500 cycles from -40° to +120°C), and lead-free solder reflow up to 260°C. Using the newly engineered “Dow Corning WG-1017 Optical Waveguide Clad Dev Sample” and the established “Dow Corning WG-1010 Optical Waveguide Core”, we were able to develop a manufacturing process suitable for large areas and offering high process control and stability to produce waveguides having optical loss values of less than 0.05 dB/cm at 850 nm VCSEL wavelength and fulfilling requirements (a) to (d) above. We describe this manufacturing process and how we have overcome the material challenges mentioned. Furthermore, we present characterization and manufacturing results, show demonstrators, and outline the potential of flexible waveguides as versatile electro-optic assembly platform.

120 Gb/s Optical Card-to-Card Interconnect Link Demonstrator with Embedded Waveguides

We report on a card-to-card optical interconnect demonstrator with passively aligned butt-coupled optoelectronic modules onto waveguides embedded into the printed circuit board (PCB). After describing selected building blocks, we will present experimental results obtained with the demonstrator hardware consisting of a parallel 12-channel at 10 Gb/s (120 Gb/s) optical card-to-card link.

FirstLight: Pluggable Optical Interconnect Technologies for Polymeric Electro-Optical Printed Circuit Boards in Data Centers

The protocol data rate governing data storage devices will increase to over 12 Gb/s by 2013 thereby imposing unmanageable cost and performance burdens on future digital data storage systems. The resulting performance bottleneck can be substantially reduced by conveying high-speed data optically instead of electronically. A novel active pluggable 82.5 Gb/s aggregate bit rate optical connector technology, the design and fabrication of a compact electro-optical printed circuit board to meet exacting specifications, and a method for low cost, high precision, passive optical assembly are presented. A demonstration platform was constructed to assess the viability of embedded electro-optical midplane technology in such systems including the first ever demonstration of a pluggable active optical waveguide printed circuit board connector. High-speed optical data transfer at 10.3125 Gb/s was demonstrated through a complex polymer waveguide interconnect layer embedded into a 262 mm × 240 mm × 4.3 mm electro-optical midplane. Bit error rates of less than 10-12 and optical losses as low as 6 dB were demonstrated through nine multimode polymer wave guides with an aggregate data bandwidth of 92.8125 Gb/s.

160-Gb/s Bidirectional Parallel Optical Transceiver Module for Board-Level Interconnects Using a Single-Chip CMOS IC

We report here on the design, fabrication and high-speed performance of a novel parallel optical module with sixteen 10-Gb/s transmitter and receiver channels for a 160-Gb/s bidirectional aggregate data rate. The module utilizes a single-chip CMOS optical transceiver containing both transmitter and receiver circuits. 16-channel high-speed photodiode (PD) and VCSEL arrays are flip-chip attached to the low-power CMOS IC. The substrate emitting/illuminated VCSEL and PD arrays operate at 985 nm and include collimating lenses integrated into the backside of the substrate. The IC-OE assembly is then flip-chip attached to a high density organic package forming the transceiver optical module. The exclusive use of flip-chip packaging for both the IC-to-optoelectronic (OE) devices and for the IC-to-organic package minimizes the module footprint and associated packaging parasitics. The OE-on-IC assembly achieves a high area efficiency of 9.4 Gb/s/mm2 (Schow et al., 2007). The complete organic carrier transceiver package provides a low-cost, low-profile module similar to a conventional chip-carrier that can be directly surface mounted to a circuit board using a conventional BGA solder process. SLC transceiver modules with transmitter and receiver OE-IC arrays were assembled and characterized. Operation of all 16 transmitters in the transceiver module was demonstrated at data rates >10 Gb/s. Similarly, all 16 receiver channels operated error-free at >10 Gb/s. The receiver eye-diagrams were generated using a second transceiver source and therefore constitute a full transceiver optical link.