Abstract
The demand for compact, energy-efficient photonic systems continues to grow with the rapid expansion of artificial intelligence (AI), data communication, radar, sensing, and emerging quantum technologies. Photodiodes (PDs), which interface the optical and electrical domains, fundamentally determine the achievable bandwidth, output power, phase noise, and integration density of these systems. This dissertation investigates the design, simulation, fabrication, and characterization of high-performance modified uni-traveling-carrier (MUTC) photodiodes, and demonstrates their heterogeneous integration on silicon nitride (SiN) photonic platforms to enable high-speed, low-noise, and fully integrated microwave, mmWave, and quantum photonics.
First, high-speed, high-power flip-chip-bonded charge-compensated (CC) MUTC photodiodes based on InGaAs/InP and GaAsSb/InP epitaxial structures were characterized. These devices exhibit low dark current, high responsivity, and bandwidths exceeding 110 GHz. Their performance under both heterodyne excitation and soliton microcomb illumination was examined. We show that soliton microcombs provide constructive interference among multiple comb lines, enabling mmWave generation up to 10.2 dBm at 100 GHz, surpassing traditional two-laser heterodyne systems while dissipating less electrical power. Using these PDs, low-phase-noise mmWave signals up to 110 GHz were demonstrated, highlighting their promise for next-generation communications and precision timing systems.
To further enable photonic integration and improve SWaP (size, weight, and power), my work investigates the heterogeneous integration of group III–V photodiodes with thick (800 nm) SiN waveguides. These devices achieve a high bandwidth–quantum-efficiency product of 49 GHz and, when integrated with a soliton microcomb, generate -18 dBm radio frequency (RF) output power at 98 GHz. Leveraging this platform, we demonstrate the first on-chip generation and detection of soliton microcombs using integrated PDs on SiN, underscoring their potential for chip-scale, low-phase-noise microwave and mmWave generation.
Finally, balanced photodiodes (BPDs) were heterogeneously integrated with Mach–Zehnder interferometers on ultra-thin (80 nm) SiN waveguides, achieving an internal responsivity of 0.3 A/W, demonstrated for the first time for laser-frequency stabilization. Subsequent integration on thick (800 nm) SiN waveguides achieved an internal responsivity of 0.91 A/W, enabling the first on-chip generation and detection of squeezed light. To support these demonstrations, I developed a new fabrication workflow with minimized optical loss that includes an airbridge formation step, achieving 100% yield both before and after this step, representing an advance toward improving PIC-level yield. Together, these achievements mark an important step toward scalable, low-phase-noise microwave-photonic and quantum-photonic systems. Overall, these results establish heterogeneous III–V/SiN photodiode integration as a promising pathway for future microwave and mmWave photonics, coherent communications, and quantum information systems.
