End-Fire Silicon Waveguides as a Platform for Optical Phased Arrays

The ability to quickly and accurately steer a laser beam is key to many applications. Speed requirements in many cases have exceeded the capabilities of conventional mechanical approaches, which has led to the introduction of nonmechanical beam steering in the form of optical phased arrays (OPAs). However, current OPAs are incapable of λ/ 2 element spacing, a key property of phased arrays, which severely impacts their steering and power capabilities. In this dissertation we introduce the concept of an end-firing silicon OPA capable of achieving half-lambda element spacing. We fabricate one-dimensional array prototypes of this class of device, and demonstrate their beam forming and steering capabilities. We also demonstrate the technology necessary to extend the concept to a two-dimensional array

Subwavelength Engineering of Silicon Photonic Waveguides

The dissertation demonstrates subwavelength engineering of silicon photonic waveguides in the form of two different structures or avenues: (i) a novel ultra-low mode area v-groove waveguide to enhance light-matter interaction; and (ii) a nanoscale sidewall crystalline grating performed as physical unclonable function to achieve hardware and information security. With the advancement of modern technology and modern supply chain throughout the globe, silicon photonics is set to lead the global semiconductor foundries, thanks to its abundance in nature and a mature and well-established industry. Since, the silicon waveguide is the heart of silicon photonics, it can be considered as the core building block of modern integrated photonic systems. Subwavelength structuring of silicon waveguides shows immense promise in a variety of field of study, such as, tailoring electromagnetic near fields, enhancing light-matter interactions, engineering anisotropy and effective medium effects, modal and dispersion engineering, nanoscale sensitivity etc. In this work, we are going to exploit the boundary conditions of modern silicon photonics through subwavelength engineering by means of novel ultra-low mode area v-groove waveguide to answer long-lasting challenges, such as, fabrication of such sophisticated structure while ensuring efficient coupling of light between dissimilar modes. Moreover, physical unclonable function derived from our nanoscale sidewall crystalline gratings should give us a fast and reliable optical security solution with improved information density. This research should enable new avenues of subwavelength engineered silicon photonic waveguide and answer to many unsolved questions of silicon photonics foundries

Machine Learning Attacks on Optical Physical Unclonable Functions

Traditional security algorithms for authentication and encryption rely heavily on the digital storage of secret information (e.g. cryptographic key), which is vulnerable to copying and destruction. An attractive alternative to digital storage is the storage of this secret information in the intrinsic, unpredictable, and non-reproducible features of a physical object. Such devices are termed physical unclonable functions (PUFs), and recent research proves that PUFs can resolve the vulnerabilities associated with digital key storage while otherwise maintaining the same level of security as traditional methods. Modern cryptographic algorithms rest on the shoulders of this one-way principle in certain mathematical algorithms (e.g. RSA or Rabin functions). However, a key difference between PUFs and traditional one-way algorithms is that conventional algorithms can be duplicated. Here, we investigate a silicon photonic PUF a novel cryptographic device based on ultrafast and nonlinear optical interactions within an integrated silicon photonic cavity. This work reviews the important properties of this device including high complexity of light interaction with the material, unpredictability of the response and ultrafast generation of private information. We further explore the resistance of silicon photonic PUFs against numerical modeling attacks and demonstrate the influence of cavity’s inherent nonlinear optical properties on the success of such attacks. Finally, we demonstrate encrypted data storage and compare the results of decryption using a genuine silicon PUF device the “clone” generated by the numerical algorithm. Finally, we provide similar analysis of modeling attacks on another well-known type of optical PUF, called the optical scattering PUF (OSPUF). While not as compatible with integration as the silicon photonic PUF, the OSPUF system is known to be extremely strong and resistant to adversarial attacks. By attacking a simulated model of OSPUF, we attempt to present the underlying reasons behind the strong security of this given device and how this security scales with the OSPUFs physical parameters