EPDA Stack: Electronic-Photonic Automation

• Electronic-Photonic Design Automation (EPDA) Stack is a unified framework combining photonic and electronic design automation, addressing unique physical and manufacturing constraints.
• It integrates methodologies such as parameterized cell creation, Manhattanization for DRV removal, and software-defined waveguide ports for accurate auto-routing.
• This scalable, technology-agnostic approach streamlines co-design in advanced CMOS systems, reducing manual intervention and enhancing manufacturability.

Electronic-Photonic Design Automation (EPDA) Stack refers to the ensemble of methodologies, tools, algorithms, and frameworks that enable the physical design, verification, and integration of photonic and electronic components within advanced integrated circuits. The EPDA stack distinguishes itself from traditional Electronic Design Automation (EDA) by addressing the physical, manufacturing, and system-level constraints unique to photonic devices (such as waveguides, resonators, and phase shifters), particularly when co-fabricated with CMOS electronics. The evolution of EPDA is pivotal to achieving scalable, manufacturable, and design-rule–clean layouts in modern systems where co-integration of electronics and photonics is essential for performance, bandwidth, and energy efficiency.

1. Integration of Photonic and Electronic Design Environments

The EPDA stack fundamentally extends EDA to natively handle photonic structures alongside electronic circuits in mainstream CAD environments, such as Cadence® Virtuoso. Photonic devices are encapsulated as parameterized cells (pCells), allowing the designer to operate with technology-independent virtual layers (e.g., for undoped Si, SiGe), which are subsequently mapped to technology-specific process layers during layout synthesis (Alloatti et al., 2015). This integration permits electronic and photonic layouts to coexist and leverage shared physical design infrastructure, including design-rule checking, hierarchical schematic capture, and netlisting.

Crucially, integration is achieved by writing custom procedures in the CAD environment’s scripting language (SKILL for Cadence), which facilitates both the generation and verification of photonic layouts. This approach supports hierarchical design, abstract device representation, and seamless connection to electronic routing resources.

2. Photonic Design Rule Violation (DRV) Removal

Photonic structures, especially those involving bends, rings, and smooth tapers, generate complex, non-Manhattan geometries that pose significant challenges for DRV checking and correction. The EPDA stack addresses these challenges through a robust algorithmic pipeline:

1. Manhattan Discretization: Arbitrary polygonal device boundaries are discretized to a Cartesian (Manhattan) grid, often at 1 nm resolution. This process converts the device’s native curves and angles into a sequence of axis-aligned line segments, making them suitable for numerical processing and Boolean logic.
2. Boolean and Sizing Operations: Once Manhattanized, Boolean operations (AND, OR, NOT) are cleanly applied, and the “size” operation is performed for DRV correction. For a minimum spacing rule of $2d$, the process grows the polygon by $d$ (which closes gaps below $2d$) and then shrinks it by $d$:

$P' = \text{Size}(\text{Size}(P, d), -d)$

where $P$ is the original polygon and $P'$ the DR-compliant result. This pipeline ensures that all shape features meet or exceed the minimum design rules, even for high vertex-count shapes ($>$4000 points).

1. Automation and Scripting Flexibility: Although demonstrated within SKILL, this algorithmic flow is implementable in any environment that supports scripting languages with polygonal and set operations.

The result is an automated, technology-agnostic procedure for design rule cleaning that is robust to the acute angles, high curvature, and device shapes endemic to complex photonic layouts (Alloatti et al., 2015).

3. Software-Defined Waveguide Ports and Auto-Routing

Photonic circuit connectivity is realized via software-defined waveguide ports, which are abstractions encapsulating physical connection points on photonic components. Each port is defined by several attributes:

• Location (coordinate—often at the endface of a waveguide);
• Orientation (propagation direction—critical for alignment of coupled structures);
• Width, layer, and device association;
• Unique identifier or label.

Procedures for handling ports are directly embedded within the scripting environment, allowing:

• Transformation and alignment operations so that interconnects between ports respect the necessary geometric and optical constraints.
• Auto-routing, in which a pathfinding algorithm computes feasible routing trajectories—straight, sinusoidal, or circular—between pairs of ports.
• Path-to-waveguide conversion, which translates the computed 1D path into the actual waveguide geometry, subject to geometric and DRV constraints.

Furthermore, for mixed-signal integration, electrical pins are also defined on photonic devices, allowing the EDA’s native electronic auto-router to handle co-designed electrical/optical elements (Alloatti et al., 2015).

4. End-to-End Workflow and CAD Integration

The described EPDA stack supports the following workflow within the electronic-photonic co-design environment:

Workflow Stage	Key Operations	Implementation
Device Definition	pCells, technology-agnostic layer assignment	SKILL/Cadence
Layout Synthesis	Hierarchical instantiation, polygon construction	SKILL
DRV Removal	Manhattanization, Boolean sizing	SKILL/generic
Port Management	Software-defined port abstraction, alignment	SKILL
Auto-Routing	Pathfinding (1D → 2D), geometry generation	SKILL
Mixed-Signal Layout	Integration with electrical routers	Cadence native
Verification	DR-check, layout-vs-schematic (LVS), DRC closure	Cadence native

This highly automated flow ensures that layout synthesis from abstract photonic and electronic design data produces a manufacturing-ready physical design that is both compliant with foundry rules and directly manufacturable in advanced CMOS process nodes.

5. Extensibility, Limitations, and Deployment Considerations

The EPDA stack’s architecture is designed for maximal interoperability:

• Language and Tooling Agnosticism: Although the reference implementation targets Cadence Virtuoso with SKILL, the geometric and algorithmic procedures (notably Manhattanization and Boolean sizing) are agnostic to the specific CAD tool, allowing migration or cross-implementation in environments supporting Python, TCL, or other scripting languages.
• Scalability: The layout cleaning and auto-routing procedures scale to devices with thousands of polygons and ports, as demonstrated in systems with several million transistors and hundreds of photonic elements (Alloatti et al., 2015).
• Process Portability: By encapsulating physical properties at the layer definition level and only translating to process-specific levels at export, designers can focus on device physics and functional topology without being encumbered by foundry-specific constraints until final layout compilation.
• Deployment: The stack is suitable for deployment in production flows for zero-change CMOS photonics and large-scale system integration, enabling the practical realization of highly complex photonic-electronic systems with stringent design rule requirements.

6. Broader Impact in Electronic-Photonic Systems

By systematically solving design rule cleaning and physical interconnect for photonics within the EDA backbone, the EPDA stack:

• Enables the co-fabrication of ultra-compact, variation-tolerant electronic-photonic circuits.
• Drastically reduces manual intervention, design time, and the likelihood of human error in design-rule–intensive environments.
• Provides a scalable path forward as the component count in photonic systems increases, satisfying the yield, performance, and manufacturability demands of high-density electronic-photonic platforms.

This approach substantiates the practical integration of photonic elements into modern, large-scale CMOS nodes and is foundational to the continued scaling and adoption of photonic-electronic co-design strategies.