A 40 Gb/s Optical Bus for Optical Backplane Interconnections

Abstract

Optical technologies have received large interest in recent years for use in board-level interconnects. Polymer multimode waveguides in particular, constitute a promising technology for high-capacity optical backplanes as they can be cost-effectively integrated onto conventional printed circuit boards (PCBs). This paper presents the first optical backplane demonstrator based on the use of PCB-integrated polymer multimode waveguides and a regenerative shared bus architecture. The backplane demonstrator is formed with commercially-available low-cost electronic and photonic components onto conventional FR4 substrates and comprises two opto-electronic (OE) bus modules interconnected via a prototype regenerator unit. The system enables interconnection between the connected cards over 4 optical channels, each operating at 10 Gb/s. Bus extension is achieved by cascading OE bus modules via 3R regenerator units, overcoming therefore the inherent limitation of optical bus topologies in the maximum number of cards that can be connected to the bus. Details of the design, fabrication and assembly of the different parts of this optical bus backplane are presented and related optical and data transmission characterisation studies are reported. The optical layer of the OE bus modules comprises a 4-channel 3-card waveguide layout that is compatible with VCSEL/PD arrays and ribbon fibres. All on-board optical paths exhibit insertion losses below 13 dB and intra-channel crosstalk lower than −29 dB. The robustness of the signal distribution from the bus inputs to all respective bus output ports in the presence of input misalignment is demonstrated, while 1 dB input alignment tolerances of approximately ±10 µm are obtained. The electrical layer of the OE bus modules comprises the essential driving circuitry for 1×4 VCSEL and PD arrays and the corresponding control and power regulation circuits. The interface between the optical and electrical layers of the bus modules is achieved with simple OE connectors that enable end-fired optical coupling into and out of the on-board polymer waveguides. The backplane demonstrator achieves error-free (BER<10-12) 10 Gb/s data transmission over each optical channel, enabling therefore, an aggregate interconnection capacity of 40 Gb/s between any connected cards.

Manufacturability and optical functionality of multimode optical interconnections developed with fast processable and reliable polymer waveguide silicones

“…The performance of silicone polymer waveguides fabricated with Dow Corning's materials has been reported on previously by mutliple groups demonstrating low optical loss at 850 nm 3,5 , ability to integrate into printed circuit boards 5 , and to meet the bandwidth needs of multiple future generatrions of high performance computing systems 6 . The materials to fabricate silicone polymer waveguides include two distinct resin formaultions: a core that retains low optical loss and stability through thermal degration and a cladding that is mechanically flexible and withstands PCB manufacturing processees.…”

Optimal design of 850 nm 2×2 multimode interference polymer waveguide coupler by imprint technique

“…Also, polymer waveguide devices can be integrated with a light source and a photo detector on a common board, which promote the reduction in cost and minimization of the optical module and subsystem [12,13]. The research on polymer based optical waveguide devices has been attracting more and more attention in the field of optical interconnection on board [14], high speed coherent receiver [15], and optical biosensor [16,17]. Especially for the optical biosensor, the polymer materials have several unique advantages.…”

Properties of the Optical Planar Polymer Waveguides Deposited on Printed Circuit Boards

“…In recent years high-performance electronic systems have highlighted the importance of developing new interconnection technologies to overcome the inherent disadvantages of copper interconnection technologies when operating at high data rates [1][2][3]. It is due to the continuous demand over the past several decades for increasingly high performance computers with more complex and integrated systems that has pushed traditional electronic interconnect links to their functional limits [4], [5].…”