Multiple-Valued Logic Physically Unclonable Function in Photonic Integrated Circuits

Physically Unclonable Function (PUF) optical circuits are described and implemented within a Photonic Integrated Circuit (PIC) to enhance certain security properties such as device authentication, anti-tamper properties, or for use as a root-of-trust value. Optical processing is advantageous for security applications such as these since they are less susceptible to eavesdropping and side channel monitoring via the difficulty of observing electromagnetic radiation emissions during PIC operation. We employ the use of State of Output Polarization (SOP) variability arising from inherent stresses, strains and manufacturing tolerances present within a fabricated PIC. A customized optical signal processing element is used in our PUF circuit that contains a very narrow "trench" structure with tiny structural variations induced during fabrication that enhances SOP variability. The tiny structural changes in fabricated PICs are fixed resulting in repeatable SOP variation of the optical signals. To avoid a need for PUF calibration, to increase robustness with respect to input power level variation, measurement device resolution and sensitivity; we show that PUF functionality can be conveniently modeled as a discrete MultipleValued Logic (MVL) function. The proposed MVL PUF formulation avoids the need to characterize and measure exact polarization states as well as enabling the use of PUF output measurement devices that have a wide range of resolution and sensitivity specifications. Several different PUF circuits are implemented within a single fabricated PIC and are experimentally evaluated to demonstrate its efficacy.