Photonic Information Processing on a Silicon Chip

We fabricate and demonstrate devices in silicon that leads towards the goal of implementing optical information processing on a silicon chip. To this effect, we demonstrate all-optical multi-level logic using a system of symmetric ring resonators in parallel. The device can form the basis of an on-chip optical digital to analog converter (ODAC). We also demonstrate ultra low cross talk by using a resonant cavity at the intersection between two strip waveguides formed in a square lattice photonic crystal structure (PhC). Two PhC structures were fabricated on silicon-on-insulator: one consists of cylindrical rods in air and another consists of cubic air holes in silicon. The device structure shown in Figure 1 consists of two independent symmetric ring resonators (SRR) arranged in a Mach-Zehnder configuration. The input light is split using a 3-dB coupler to the two rings. The field dropped by the individual ring resonators interferes constructively at the output port. When the two resonators have the same resonant wavelength, the system has maximum transmission (one). Multi-level logic is achieved by independently switching the individual ring resonators off resonance. If one ring resonator is switched off, then the transmission of the system is half. And consequently if both resonators are switched off, the transmission is zero. Figure 1: SEM image of the fabricated device. Summary of Research: Recent advances in the field of silicon photonics have enabled the integration of compact, high speed optical devices on chip [1,2]. These devices have a range of applications in optical interconnects, optical signal processing, sensing and logic applications. It is therefore conceivable that optical data processing will become increasingly prevalent. In this research, we fabricate photonic crystals and ring resonators to achieve the goal of information processing on a silicon chip. Optical Multi-level Logic on a Silicon Chip: In this project, we demonstrate an all-optical multi-level logic in silicon using a system of ring resonators that can form the basis of an optical digital-analog converter (ODAC). Figure 2: Temporal response illustrating switching to different amplitude (logic) levels. Inset shows the individual resonant wavelengths corresponding to multiple logic levels.