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Integrated Silicon Photonic Optical Phased Array, Devices, Circuits and Systems, for Free-Space Optical Communication

Wuxiucheng Wang

Supervised by Hui Wu

601 Computer Studies Building

Future networks require higher bandwidth, lower latency, high accessibility and support for agile reconfiguration. Free-space optical communication (FSOC) emerges as a viable solution for both access and back-bone networks due to its superior bandwidth in the optical domain and reduced latency through air medium. Current FSOC systems may fall short in meeting the requirements for agility and dynamics due to their reliance on bulky mechanical motion systems. Silicon photonic Integrated Optical Phased Arrays (OPAs), featured by their cost-effectiveness, compatibility with CMOS circuits, and instantaneous solid-state beamsteering, are increasingly recognized as one of the most promising technologies for future FSOC applications. 

This dissertation discusses three key topics: (1) the design and implementation of an integrated silicon photonic OPA system and how to make it work. (2) a cascaded subarray architecture for OPA designs to achieve various system-level optimizations. (3) a new approach for broadening OPA beamsteering range using complementary grating emitters (CGEs). 

In the first topic, the theoretical part covers the fundamentals and far-field synthesis methods for OPA simulations. The hardware and software discussions are divided into three parts: the device part discusses the design and optimization of OPA components: thermo-optic/electro-optic phase shifters (TOPSs/EOPSs) and grating emitters; the circuit part covers photonic and peripheral electronic circuit designs and implementations; and the system part explains the OPA control method, software program, experimental test setup, calibration. FSOC experiments, such as spatial multiplexing and bit-error-rate measurements, are also demonstrated. 

The following two topics are built upon the previous infrastructure, and both contribute to FSOC system performance: the cascaded subarray architecture incorporates phase shifters into an OPA’s optical power distribution network (OPDN) as subarrays. By trading off the number of controls, this architecture significantly reduces power consumption and thermal crosstalk in a TOPS-based OPA circuit, and reduces the OPA footprint size and dynamic power consumption in an EOPS-based OPA. The CGE pairs, leveraging the ±1 diffraction orders and layout arrangement, increase the emitter density within the OPA aperture. Due to their proximity and far-field peak mismatch, the resulting grating lobes are further separated, enabling a broader beamsteering range.