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38 DESIGN007 MAGAZINE I JANUARY 2025 ere are multiple design challenges to address when developing an EOCB. ese include: • Electrical: Optimizing the path for RF and electrical signal transmission • Optical: Ensuring signal optimization, free-space collimation, and effective opto- mechanical system design • ermal: Considering heat sources and integrating sinks as needed An essential technology for EOCBs is the fabrication of waveguides in the glass layer (Figure 3), akin to the optical equivalent of printing circuits on a PCB. You can tailor wave- guides for single-mode (SM) or multi-mode (MM) transmission. While datacom structures use multi-mode signals, silicon photonics pri- marily rely on single-mode signals. Lasers or other technologies can produce waveguides in glass, including by an ion exchange process that originated from semiconductor processing. e latter has the advantage of parallel processing, whereas laser processes are inherently sequen- tial, as the laser must trace the waveguide path. Microelectronics and printed circuit boards have developed dramatically over the 50 years I have been in the industry. In the future, EOCBs will be crucial for effective data pro- cessing. One significant requirement is the development of integrated optical connections between electrical or photonic processing and storage units at various levels, from chips and chiplets (system on chip) through interpos- ers to full panels. Waveguides made using an ion-exchange process in inexpensive display glass laminated with conventional PCB mate- rials can address this need. However, greater changes are on the horizon. As data usage and sharing for AI increase, optical conductors will increasingly complement electrical routing. Key Points • e limitations of copper PCBs have become increasingly clear. • Optical interconnects and photonic inte- grated circuits are setting the stage for the next generation of PCBs. • e bottleneck lies in the interconnects between the ultra-high-speed devices. • Multilayer electro-optical PCBs use light rather than electrical energy to transmit data. • At very high data transfer rates, optical interfaces can be significantly more efficient than electrical ones. Figure 3: Glass-integrated optical waveguides fabricated by ion-exchange. Source: Fraunhofer IZM