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 four 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 four-channel three-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.
© 2014 IEEE
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