Hardware assurance with silicon photonic physical unclonable functions

In the modern landscape of optical communication networks, ensuring robust security is increasingly critical, particularly for applications requiring seamless integration and minimal attack surfaces. Photonic Physical Unclonable Functions (PUFs) leverage the response from the photonic devices that are prone to inherent physical variations to generate unique and unpredictable signature identifiers which are then utilized by an authentication system for identification or encryption purposes. These photonic PUFs can be cohesively integrated into systems that use optical communication, whereas using electronic PUFs would introduce additional vulnerabilities due to the need for signal-domain conversions between optical and electronic signals. In this paper, we present the design, fabrication, and experimental evaluation of advanced silicon-photonic-based PUFs utilizing Contra-Directional Coupler (CDC) structures. These structures offer a complex design space and are intrinsically sensitive to fabrication-process variations, making them ideal for creating unique and secure responses. We introduce several innovative design enhancements, including randomized corrugation functions, perforated designs, and ring-assisted CDCs, to increase the complexity and unpredictability of the CDC response. Measurement results from the fabricated CDCs demonstrate their capability to achieve an average Hamming distance threshold of over 0.2, effectively distinguishing between legitimate devices and their copies. We rigorously tested these fabricated designs against three different machine-learning-based attack scenarios. The results showed a Hamming distance of over 0.4 with a standard deviation of less than 0.01 at a quantization level of three, using 10,000 samples of challenge-response pairs. These findings underscore the potential of silicon photonic PUFs in enhancing security for optical communication systems of different scales. The integration of such photonic PUFs offers robust and reliable security solutions for applications where traditional electronic methods introduce additional attack surfaces and fail to provide adequate protection.