Optical Interconnects for In-Plane High-Speed Signal Distribution at 10 Gb/s: Analysis and Demonstration

Abstract

In this dissertation, the development of an experimental prototype for on-board optical-to-electrical signal broadcasting at 10 Gb/s per channel over an interconnect distance of 10 cm was presented. The optical distribution network was implemented using a polymer-based 1-by-4 multimode interference (MMI) splitter with linearly tapered output facet. A 1-by-8 MMI splitter with input/output waveguides of 10 microns in width was first fabricated using standard photolithography and characterized at 40 Gb/s in NRZ format and PRBS = 2^7-1. The pulse response of MMI devices was further quantified from the time-dependent, pulse-modulated field propagation perspective incorporated with various dispersion mechanisms. The results predict their operating limitations and investigate why and how such devices become non-functional in the ultrashort-pulse limit that is far beyond the most present-day optical systems. The guided-mode attenuation associated with polymer waveguides fabricated on FR-4 printed-circuit boards was also investigated for the first time. The rigorous transmission-line network approach was applied and the FR-4 substrate was treated as a long-period substrate grating with rectangular corrugations. The peaks of attenuation were shown to occur near the Bragg conditions that were recognized as the leaky-wave stop bands. As the buffer layer thickness increases, the attenuation becomes negligibly small that is attributed to the weak grating-induced perturbation to the mode behavior. The prototype was then developed on the basis of both experimental verifications to the devices and theoretical investigations. An improved 1-by-4 MMI splitter at 1550 nm with linearly tapered output facet was heterogeneously integrated with four p-i-n photodetectors (PDs) on a silicon (Si) bench. The Si bench itself was then hybrid integrated onto an FR-4 printed-circuit board with four receiver channels composed of transimpedance amplifiers, limiting amplifiers, and surface-mounted components. The innovative integration approach demonstrated the simultaneous alignment between multiple waveguides and multiple PDs during the MMI fabrication process that is a complete radical departure from the conventional assembly method inherent from the telecommunication industry. The entire system was fully functional at 10 Gb/s per channel.