Silicon photonics (Sipho)—the fusion of optical communication and CMOS electronics—is rapidly emerging as a cornerstone of next-generation computing, sensing, and connectivity. From AI datacenters to autonomous vehicles, the demand for high-bandwidth, energy-efficient photonic integration is skyrocketing. Now, with the launch of the STARLight project, Europe is making a bold move to industrialize this technology at scale. Led by STMicroelectronics and backed by the EU CHIPS Joint Undertaking, STARLight gathers 24 partners across 11 countries to establish a 300mm Sipho manufacturing ecosystem. The goal is ambitious: to transform Europe from a research powerhouse into a world-class global production hub for photonic innovation.
Embedded.com spoke with Sylvie Gellida, General Manager of STMicroelectronics’ Optical and RF Foundry Division within the RF and Optical Communication product group. The discussion focused on how STMicroelectronics’ core competencies will be aligned with contributions from other participants, as well as on the application domains impacted by the project.
Historical Perspective: The Rise of Silicon Photonics
Sipho emerged in the early 2000s as a promising solution to the growing bottlenecks in electronic data transmission. Initially confined to academic labs and niche applications, the technology leveraged the vast infrastructure of CMOS manufacturing to integrate optical components—like waveguides, modulators, and detectors—directly onto silicon chips.
Initial breakthroughs focused on short-reach optical interconnects for datacenters, but progress was slow due to fabrication challenges and limited commercial demand. Over the past decade, however, the convergence of AI workloads, cloud computing, and edge devices has reignited interest, pushing Sipho from proof-of-concept to production-ready. Today, with initiatives like STARLight, Europe is accelerating this transition, aiming to industrialize SiPho on 300mm wafers and embed it across sectors from autonomous vehicles to quantum communications.
How Silicon Photonics Works
Sipho integrates optical communication components onto silicon substrates using CMOS manufacturing processes, enabling high-speed data transfer with low power consumption. At its core, the technology replaces electrical interconnects with optical waveguides—patterned into silicon—that transmit data as light rather than electrons.
Waveguides, the pipelines of photonics, guide light across the chip. In traditional waveguides used in RF and microwave systems, electromagnetic waves propagate through confined structures, with electric and magnetic fields oscillating perpendicular to each other and to the direction of travel. These fields are guided by boundary conditions imposed by the waveguide’s geometry, allowing specific modes to travel with minimal loss.
Sipho waveguides operate on the same principle, but at optical frequencies and within dielectric materials. Light is confined in a high-refractive-index silicon core surrounded by lower-index cladding (typically silicon dioxide), creating total internal reflection that traps and steers the optical mode. The confined electric field oscillates within the waveguide cross-section, with a specific spatial distribution known as the mode profile. This profile is carefully engineered to achieve key performance goals:
Optimal coupling, ensuring light can be transferred efficiently from an external source (like an optical fiber) onto the chip.
Minimal dispersion, which prevents the optical signal from blurring as different frequencies (colors) of light travel at slightly different speeds.
Seamless integration, ensuring the light effectively interacts with and overlaps other on-chip components like modulators and detectors.
Key components include modulators, which encode electrical signals into optical ones (often via carrier depletion or injection in silicon—techniques where the number of electrons and holes in the silicon is decreased or increased to alter its refractive index and thus modulate the light); photodetectors, typically made of germanium-on-silicon, which convert light back into electrical signals; and multiplexers and filters, which combine or separate wavelengths for dense data transmission.
Because all these elements are fabricated using CMOS-compatible processes, Sipho enables scalable integration with electronic circuitry. This combination delivers high bandwidth, low latency, and reduced thermal load, making it essential for next-generation computing architectures in AI, HPC, and edge environments.
On the primary role played by STMicroelectronics and the support of partners, Dr. Gellida said:
"STMicroelectronics brings its proprietary silicon photonics technology and a unique integrated device manufacturer (IDM) model, enabling high-volume 300mm wafer manufacturing in Europe. ST’s technology allows the integration of multiple complex components into a single chip, enabling better integration capability, higher throughput, and better power efficiency. Partner’s technologies are integrated through a collaborative innovation ecosystem, with key Tech-leaders and Universities contributing expertise in materials, design, and manufacturing to accelerate photonics development. The consortium focuses on addressing key technical challenges such as high-speed modulation, laser integration, new materials, and packaging/integration of PICs with electronic circuits to build a seamless value chain".
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