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To detail results of research into optical waveguides fabricated from silicon on insulator (SOI) for on‐chip high speed applications and from polymer for more general applications.

This paper shows the processes for wet etch fabrication of SOI single mode rib waveguides including compact crystal plane turning mirrors. Losses for the mirror facets are determined by difference measurements. Multimode polymer strip waveguides are fabricated on glass substrates by conventional photolithography using SU8 polymer and tested for attenuation.

Fabrication of compact turning mirrors for silicon waveguides requires precise alignment of masks and controlled etching of the corner facets in order to obtain correct alignment of the mirror face with the incoming and outgoing waveguides. Measurements of losses per mirror facet show typical losses of 1‐2 dB/facet. Suggestions for improvements are made. Preliminary results for polymer waveguides show the necessity for high quality lithography.

Optical interconnects for high speed communication on board and on chip are part of the ITRS Road Map for advanced interconnects. Design of optical elements to enable this, including reduction of on‐chip area by turning mirrors, is necessary for on‐chip optical technology to be successful. Compact etched mirrors described here extend previous designs and enable fabrication at any position on‐chip. New etch mask techniques for silicon waveguide fabrication are also described.

To characterise the optical performance of organic multi‐mode optical waveguides integrated with printed circuit board (PCB) and to demonstrate the feasibility of 2.5 and 10 Gbps optical interconnection in board‐level, respectively.

This paper provides both qualitative and quantitative approaches for the characterization the wave guide performance, i.e. using loss measurement, optical beam profiling, ethernet verification, and eye‐diagram testing. In addition to wave guide loss measurement, the most significance part of the work reported in this paper is to evaluate optical wave guides with coupled VCSELs, by which a 3 dB coupling design budget can thus be identified. Furthermore, by artificially manipulating coupling conditions, practical concerns of EOPCB integration, including waveguide geometry, VCSEL driving power, alignment tolerance, coupling spacing, etc. are studied.

Thermal stability studies related to PCB lamination processes show the feasibility of organic waveguides integrated to traditional PCB manufacturing. For a direct VCSEL/PD coupling scheme, a 3 dB power budget is experimentally identified. For short reach optical interconnection, 10 Gbps up to 17 cm propagation on PCB can be achieved by using 50×50 μm multi‐mode organic waveguides, where a±25 μm tolerance of optical alignment is compatible to the design rules of PCB.

The value of the paper lies in its systematic approaches to identify the waveguide performance through both qualitative and quantitative indices. The correlation between geometry design, processes, coupling conditions, and optical performance of organic waveguides explored in detail. Not only is a standard eye‐diagram test used to verify the waveguide at 2.5 and 10 Gbps bandwidth, but also a prototype of optical data‐communication on giga‐ethernet is demonstrated for long term stability. Following these analytical methods, readers can understand more about the optical performance of waveguides when designing optical interconnection for high speed electro‐optical integrated PCBs.

The purpose of this paper is to provide an overview of the research in a project aimed at developing manufacturing techniques for integrated optical and electronic interconnect printed circuit boards (OPCB) including the motivation for this research, the progress, the achievements and the interactions between the partners.

Several polymer waveguide fabrication methods were developed including direct laser write, laser ablation and inkjet printing. Polymer formulations were developed to suit the fabrication methods. Computer‐aided design (CAD) tools were developed and waveguide layout design rules were established. The CAD tools were used to lay out a complex backplane interconnect pattern to meet practical demanding specifications for use in a system demonstrator.

Novel polymer formulations for polyacrylate enable faster writing times for laser direct write fabrication. Control of the fabrication parameters enables inkjet printing of polysiloxane waveguides. Several different laser systems can be used to form waveguide structures by ablation. Establishment of waveguide layout design rules from experimental measurements and modelling enables successful first time layout of complex interconnection patterns.

The complexity and length of the waveguides in a complex backplane interconnect, beyond that achieved in this paper, is limited by the bend loss and by the propagation loss partially caused by waveguide sidewall roughness, so further research in these areas would be beneficial to give a wider range of applicability.

The paper gives an overview of advances in polymer formulation, fabrication methods and CAD tools, for manufacturing of complex hybrid‐integrated OPCBs.

To investigate the influences of environmental stresses on board‐embedded polymeric waveguides.

Optical multimode waveguides were embedded on printed circuit boards using commercial polymers. The optical‐PCBs varying in board structure and in optical build‐up materials were exposed to heat, moisture and ionic‐contaminants in accelerated reliability tests. The influence of stress factors on the structural integrity and functional parameters, namely the refractive index and optical transmissivity, was investigated at the key communication wavelengths.

Isothermal annealing reduced the refractive index to the greatest extent. The optical‐PCB structure with an optical surface build‐up layer was observed to be more vulnerable under temperature shock when compared with the optical‐PCB with optical inner layer. The buffer layer beneath the optical build‐up was found to improve the stability of the optical waveguides significantly. The results indicated of wavelength dependence to the aging factor with a failure mechanism. The factors affecting the performance and reliability of polymer‐based optical waveguides on PCBs were discussed.

More experimental data and investigations of failure mechanisms are required to ultimately obtain sufficient reliability statistics for accurate life‐time prediction models.

Optical interconnects are seen as a promising solution to overcome performance limitations encountered with high‐frequency electrical interconnections. As an emerging technology, only a limited amount of reliability data on optical/electrical packages is available. The paper investigates the influences of environmental stresses on board‐embedded polymeric waveguides.

The purpose of this paper is to study fabrication of optical‐PCBs on panel scale boards in a conventional modern PCB process environment. It evaluates impacts on board design and manufacturing with the developed optical board verifiers outlining challenges and requirements for manufacturing low‐loss waveguide structures and optical building blocks. The study aims to expand the current knowledge in the field by adding results obtained by utilizing industrial production infrastructure and developed scalable manufacturing processes to fabricate optical‐PCBs and board assemblies in high‐volumes and low‐cost manner.

Impacts on board design and manufacturing were studied with the developed optical technology verifiers. One verifier is optical‐PCB with embedded waveguides, integrated i/o couplers and optical vias. Another verifier is large size PCB with optical layer. A system‐level optical board assembly with 12.5 Gb/s Tx/Rx devices on surface mounted ball grid array (BGA) modules is designed for optical link analysis. Fabricated optical structures on verifiers are evaluated of their physical characteristics utilizing optical, SEM, LSCM analysis methods. Performance testing is conducted using standard optical transmission measurement methods and equipment.

The paper provides empirical results about fabrication of multimode optical waveguides with conventional PCB process equipment. Results suggest that current coating and imaging equipments are capable of producing optical waveguide patterns with high resolution and size accuracy. However, fabricators would require larger process window and defect tolerance for processing optical materials to obtain low‐loss waveguides with sufficient yields.

Because of the limited amount of design variants in production verifiers evaluated in this paper, some impacts like effect of base material, board construction, optical layer location and beam coupling solution were not evaluated. Likewise, impacts on long‐term stability and cost were not addressed. These factors however require further investigation to address technical feasibility of optical PCBs technology prior commercial high volume production.

The paper includes implications for the development of a fabrication methods and testing procedures for optical polymer waveguide layers on PCBs.

This paper fulfils need to provide results on design, fabrication and characterization of optical PCBs and backplanes from industrial fabricator's perspective. The paper provides input for end‐user and developers to evaluate technical performance, robustness, and maturity of building blocks and supply chain to support polymer waveguide based technology for intra‐system optical links.

Radio frequency (RF) technology relies on the electromagnetic properties of the materials used, which includes their complex permittivities and loss tangents. To measure these properties, techniques for material characterization such as the transmission/reflection method are used in conjunction with conversion techniques to calculate these values from scattering parameters. Unfortunately, these techniques rely on relatively expensive rectangular waveguide adaptors and components, especially if testing over large frequency ranges. This paper aims to overcome this challenge by developing a more affordable test equipment solution based on additively manufactured waveguide sections.

To evaluate the effectiveness of using additively manufactured waveguides to perform electromagnetic characterization with the transmission/reflection method, samples of PLA Tough with varying infill percentages and samples made from several Formlabs photopolymer resins are fabricated and analyzed.

Results show that the method yielded permittivity and loss tangent values for the measured materials that generally agree with those found in the literature, supporting its credibility.

The accessibility of this measurement technique will ideally allow for more electromagnetic material characterization to occur and expand the possible use of additive manufacturing in future RF designs. This work also provides characterization of several Formlabs photopolymer resins, which have not been widely analyzed in the current literature.

There are a number of organic, inorganic and hybrid inorganic waveguide materials that are currently being used for a wide variety of optical interconnect applications. Depending upon the approach, waveguide formation is performed using a combination of lithographic and/or reactive ion etch techniques. Often the processes involved with waveguide formation require unique processing conditions, hazardous process chemicals and specialized pieces of capital equipment. In addition, many of the materials have been optimized for silicon substrates but are not compatible with printed wire board (PWB) substrates and processes.

We present in this paper an efficient finite element analysis for different types of waveguides . The computations are performed with “edge elements” . These finite elements avoid all the “spurious modes”, the non‐physical numerical fields obtained from the solution of eigenvalue problems with classical finite elements formulations.Both dielectric‐loaded waveguides and ridged waveguides (waveguides with sharp edges) are analyzed. Comparisons of our results with previously published ones show theaccuracy of the numerical technique.

To present work and characterisation results from a project to develop a pluggable optical connector for board to board interconnect.

An optical backplane connection system is described, which allows for repeatable docking and undocking of an active optical interface housed on a daughtercard to waveguides fabricated on an optical backplane.

The optical backplane connection system described has demonstrated its successful implementation with respect to optical data transfer across multimode polymer waveguides. Measurement results presented show that such a system is a viable approach toward the application of pluggable optical backplane interconnects.

The direct connection to the exposed waveguide interface results in considerable optical loss and scattering. Future designs will have to address this. Additional work should also be undertaken to develop a means of connector engagement that is autonomous and requires no user intervention.

Prior research into the problem of coupling to an optical backplane has been concerned with interfaces that deflect optical signals by 90° into and out of the waveguides. Here, an alternative approach is proposed that launches light directly into the waveguide ends.

In microwave radio‐frequency technology, the design of broadband circular polarisers involves the use of waveguides having different propagation velocities for two orthogonal, linearly‐polarised modes. To achieve this aim, square ridged waveguides with dielectric inserts may be employed to disturb the symmetry of the dual linear polarisations. The computation of the cut‐off frequencies of the structure is achieved by the use of a finite‐element method which makes full use of powerful pre‐ and post‐processing techniques.