Polymer optical waveguides with reduced in-plane bend loss for electro-optical PCBs

Abstract

In-plane bend loss represents the greatest commercial inhibitor to deploying multimode optical waveguides on densely populated electro-optical printed circuit boards (OPCB) as the minimum bend radii currently possible are too large to be practical in common designs. We present a concept and fabrication method for creating novel polymer optical waveguide structures with reduced bend losses to enable higher density routing on an OPCB. These nested core waveguide structures comprise a core surrounded by a thin shell of cladding, which allows for twofold modal containment by first a conventional low refractive index contrast (LIC) boundary followed by a secondary high refractive index contrast (HIC) boundary. The purpose of this is to reduce the in-plane bend losses incurred on tightly routed optical channels, while not incurring prohibitive dispersion, sidewall scattering and optical crosstalk penalties. We have designed and fabricated nested core multimode polymer waveguides, evaluated their performance in comparison to conventional step-index waveguides and simulated these structures using the beam propagation method. Preliminary results are presented of our measurements and simulations.

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

“…In-plane bends are an inextricable requirement in complex waveguide layouts on OPCBs; however, bend radii as large as the minimum bend radius of 17 mm deployed on the First-Light midplane would be difficult to accommodate within a high density PCB layout, especially where high numbers of optical waveguides are involved. Research into novel waveguide structures allowing a reduction in bend loss and corresponding reduction in minimum bend radius is currently underway to address this issue [29].…”

“…Though the relatively large minimum bend radii required at this stage would place significant routing constraints on future optical PCB layouts, these could be effectively mitigated by refinement of manufacturing techniques or novel structuring of the waveguide to reduce bend loss as demonstrated by Xyratex [29].…”

Integrated in‐plane mirror and multimode waveguide fabrication using 248 nm excimer laser ablation for optical interconnects on PCBs

“…One approach to achieve this would be to prepare a separate straight waveguide by laser ablation alongside the waveguide containing the mirror; the former can then be used as a reference for which losses due to the mirror can be obtained. It will be interesting to compare the losses associated with these structures to those already obtained with curved waveguides of different radii (Papakonstantinou et al, 2006(Papakonstantinou et al, , 2007Pitwon et al, 2012) to determine which contributes most to the total loss budget of the system. To improve manufacturing throughput, this inplane coupling technique could also be applied to fabricated mirrors in waveguides pre-prepared by other methods such as photolithography.…”

“…out-of-plane coupling, but also within a layer (in-plane routing); the latter would be extremely important if OI is extended to the chip level. In-plane routing can be achieved with curved multimode waveguides, but the signal losses are affected by the radii of curvature (Papakonstantinou et al, 2006(Papakonstantinou et al, , 2008Pitwon et al, 2012). The fabrication of in-plane mirrors as an alternative approach was therefore the primary objective of the work reported in this paper.…”

Compact and Fabrication-Tolerant Waveguide Bends Based on Quadratic Reflectors

“…In the first case, air trenches, where waveguide cladding material is removed and replaced with air, act to boost the refractive index contrast between the waveguide core and clad at the bend sections, thereby decreasing the radiative bending loss. The strategy has been successfully applied to waveguides made in polymers [28]- [30], silica glass [31] and oxynitride [32]. Similar concepts have also been adapted to shallow rib waveguides [33], [34] and laser-written glass waveguides [35].…”