ROBERT BLUM LIGHTWAVE LOGIC
Beyond PN Junctions: Bringing 400G Modulators into the Silicon Photonics Design Flow
A rtificial intelligence is As AI clusters continue to scale, the industry is rapidly moving beyond 200G toward 400G-per-lane optical interfaces, placing unprecedented demands on bandwidth, power efficiency and integration density. While silicon reshaping the requirements for optical interconnects. photonics has firmly established itself as the dominant platform for high-volume optical transceivers, the performance limits of conventional carrier-depletion PN-junction modulators are becoming increasingly apparent. The challenge is no longer simply developing faster modulators. Designers increasingly want technologies that integrate seamlessly into the silicon photonics platforms, foundries and design environments they already use. Performance alone is no longer enough; manufacturability, interoperability and design enablement have become equally important. Among the technologies attracting growing attention are electro-optic (EO) polymers. Rather than replacing silicon photonics, EO polymers complement existing foundry platforms by introducing a highly efficient modulation mechanism while leveraging the scalability and manufacturing maturity of CMOS- compatible silicon photonics. Unlike carrier-depletion PN-junction modulators, silicon-organic hybrid (SOH) devices exploit the linear electro- optic (Pockels) effect within engineered organic materials. Because modulation occurs through direct electric-field interaction rather than carrier transport, the material itself introduces virtually no practical bandwidth limitation. Device performance is instead determined largely by RF design and electrical parasitics, enabling compact modulators with bandwidths exceeding 100 GHz while maintaining exceptionally low drive voltages. At the same time, the polymers can be deposited using standard spin- coating processes already familiar to CMOS foundries, while atomic layer deposition (ALD) encapsulation has demonstrated long-term environmental stability, with recent results exceeding 2,000 hours of damp-heat testing.
Perhaps the most significant development, however, is not the device performance itself, but the maturation of the surrounding design ecosystem. For many years, promising photonic device technologies remained confined to research laboratories because they lacked the infrastructure needed for commercial product development. Today, advanced modulation technologies are increasingly becoming available as reusable building blocks within foundry- qualified photonic process design kits (PDKs). Rather than manually creating custom layouts, designers can now incorporate verified components—including slot waveguides, mode converters, phase shifters and complete Mach– Zehnder modulators—directly into the same design environments used for conventional silicon photonics. Recent industry collaborations illustrate how quickly this ecosystem is evolving. During a recent Luceda Photonics webinar, engineers demonstrated a fully parameterized design flow in IPKISS that generated polymer-enhanced modulators from reusable photonic PDK components,
Very compact silicon-organic modulators are now part of the PDK of several foundries allowing for 200G and 400G per lane PIC designs.
fabrication flows. Increasingly, the goal is to integrate advanced materials into existing silicon photonics ecosystems, allowing engineers to evaluate, simulate and tape out next-generation modulators using the same foundry- qualified workflows they already rely on for production devices. As AI infrastructure continues its rapid evolution toward 400G-per- lane optical interfaces and beyond, innovation will depend on more than improvements in device performance alone. Success will require technologies that combine higher bandwidth, lower power consumption and manufacturing scalability with practical engineering tools that accelerate adoption. The emergence of foundry-ready photonic PDKs for advanced modulation technologies represents an important milestone in that journey—bringing new device architectures into mainstream silicon photonics design flows and enabling engineers to focus less on process development and more on designing the next generation of photonic integrated circuits.
allowing designers to optimize complete devices while remaining entirely within familiar silicon photonics workflows. Likewise, the recent collaboration between GDSFactory, GlobalFoundries and Lightwave Logic extends this concept to another widely used design environment, providing designers with foundry-ready EO polymer device libraries on GlobalFoundries’ silicon photonics platform. Together with similar initiatives across multiple foundries, these efforts demonstrate an important industry transition: advanced modulation technologies are no longer isolated research devices, but are becoming accessible through standardized photonic PDKs that support commercial design and manufacturing. This represents an important shift for the industry. Historically, adopting a new material system often required designers to learn entirely new processes and
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ISSUE 44 | Q3 2026
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