ECE PhD Thesis Defense: Xinchang Zhang

ECE PhD Thesis Defense: Xinchang Zhang

Title: CMOS Optoelectronics for Scalable Wireless Systems

Presenter: Xinchang Zhang

Advisor: Professor Miloš Popović

Chair: Professor Lei Tian

Committee: Professor Miloš Popović, Professor Roberto Paiella, Professor Tianyu Wang, Professor Ali Niknejad, Professor Jun-Chau Chien

Google Scholar: https://scholar.google.com/citations?hl=en&user=9fIvuNIAAAAJ&view_op=list_works&sortby=pubdate

Abstract: Electromagnetic wave with wavelengths between 10 mm and 1 mm, known as millimetre-wave (mm-wave), have become an emerging carrier for the next-generation wireless systems which communicate and sense. mm-Wave not only provides large spectral bandwidth, but also favours large element-count antenna arrays, whose beamforming compensates for mm-wave propagation loss and provides high spatial resolution to serve multiple users. In principle, the most flexible architecture is a fully digital array, in which every antenna element has dedicated radio-frequency (RF) electronics and high-speed data converters, and beamforming is performed in a digital backend. In practice, however, scaling such arrays to hundreds or thousands of elements is fundamentally constrained by limited available area, power consumption, heat dissipation, and the input/output bandwidth for the resulting digital samples. Here we show a photonic architecture for scalable mm-wave array receiving that is implemented in a volume complementary metal-oxide-semiconductor (CMOS) platform. In this architecture, one ultra-compact mm-wave-to-photonic transducer per antenna element reads the mm-wave received directly onto an optical carrier, leaving no data converter or digital electronics at the array. The transducer is built around a triple-cavity micro-ring electro-optic modulator that is specifically designed for robust and efficient RF-to-photonic transduction, and is monolithically integrated with a low-noise amplifier on the same CMOS chip. The modulator operating frequency can be reconfigured in situ through controllable resonance spacing, enabling both operation across a wide RF carrier range and compensation for fabrication variations across channels and dies. With a single transducer, we demonstrate a mm-wave receiving link in which on-array transduction is combined with remote photonic signal processing, recovering an 8 GBaud 16-QAM signal on a 59 GHz carrier at a bit error rate of 1.68 x 10^{-4}, below the forward-error-correction threshold. We further implement the link in a 1 x 4 antenna array using four photonic channels, obtaining signal-to-noise ratio improvement and simultaneous multi-user support in both communications and sensing. By simplifying the radio head down to an ultra-compact CMOS transducer, our architecture combines the manufacturing scale of silicon chips with the per-element amplitude and phase information of a digital array, providing a general-purpose frontend for future wireless systems.