Low Loss, Broadband, and Non-Volatile ‘Directed Logic Operations’ Using Phase Change Materials in Silicon Photonics

In this paper, we present novel architectures for non-volatile directed logic circuits, that demonstrate low insertion losses, high extinction ratios, as well as multi-bit and broadband operations. The non-volatile switching operations are performed using a non-volatile phase change material Ge2Sb2Se4Te1 (GSST). The phase of the GSST is controlled by electro-thermal switching (from amorphous to crystalline and vice versa) using graphene micro-heaters. We demonstrate all the fundamental logic operations (such as OR, AND, XOR, NOR, NAND, and XNOR), adder, comparator, and parity checker with multi-bit operation capability. Moreover, we demonstrate directed logic architectures that can perform multiple logic operations (which includes providing inverted outputs) using the same logic circuit. The designs of the logic circuits show low insertion losses (< 1 dB) and high extinction ratios ( $>$ 10 dB) with broadband operations ( $\sim $ 100 nm) operating in the telecommunication C-band. To the best of our knowledge, this is the first demonstration of the broadband operation for photonic directed logic circuits. For cascading multiple logic operations, the proposed architectures are ideal in terms of logic delay, extinction ratios and the ability to drive the number of other circuits. This study provides a practical technique to design future high-speed nanoscale non-volatile photonic integrated circuits for logic computing applications.