Advanced silicon photonics for microwave frequency down-conversion

Abstract

Microwave photonics is broadly defined as the study of optical devices operating in the microwave to millimeter wave spectrum, and interest in this field is continually driven by the need for higher electrical frequencies and larger signal bandwidths. However, electronic systems designed to meet these specifications are becoming increasingly challenging to create, while their microwave photonic counterparts offer a larger bandwidth, lower power consumption, higher linearity, and smaller footprint. Thus, microwave photonic systems are an attractive solution for challenging problems in the domain of high-speed electronics. This thesis will examine a specific component of a microwave photonic system, a frequency down-converter. This device takes two electronic input signals and outputs the difference between the two input frequencies. To date, all demonstrations of a photonic microwave frequency down-converter have been based on bulk optical devices that limit its deployability to a real-world application due to a large footprint. However, recent advances to silicon photonic fabrication processes stand to improve the performance and enable the mass-production of many different microwave photonic systems including a frequency down-converter. In this thesis, a library of passive CMOS-compatible silicon photonic components for microwave photonic systems was developed. Additionally, a high-saturation power germanium-on-silicon photodetector showing a 70% improvement in photocurrent generation under high incident powers, and a depletion mode optical phase shifter with a V[subscript [pi]]L of 0.9 V xcm and an electro-optical bandwidth of several gigahertz were designed and tested. Finally, all of these components were assembled in a novel architecture to create an integrated silicon photonic microwave frequency down-converter. Initial measurements of this structure showed an electrical-to-electrical conversion efficiency of -42 dB and a suppression of spurious frequencies of approximately 15 dB.