Optical Method for Antenna Near-Field Sensing

Abstract

This thesis explores the application of Thin Film Lithium Niobate (TFLN) in advancing the fabrication of optical devices for electric field (E-field) sensing within phased-array antenna systems. The research primarily focuses on the deployment of fully dielectric TFLN-based Mach-Zehnder Interferometer (MZI) waveguides to detect E-field variations, representing a shift from conventional metallic-based sensing approaches. By leveraging the electro-optic (EO) effect inherent in TFLN, this study assesses the capability of these waveguides to passively modulate the power of an optical signal in response to E-field alterations, with the goal to contribute to the enhancement of E-field sensing technology.

The methodology incorporated a comprehensive phase of design, simulation, fabrication, and experimental validation. Simulations were conducted using HFSS for analyzing antenna performance and Lumerical to measure optical device behaviour, establishing the fundamental groundwork for device optimization. The fabrication stage was elaborately engineered, utilizing electron beam lithography with HSQ, ZEP, and SiO2 processing techniques, among which the ZEP process method was identified as providing optimal outcomes in producing precise optical device structures with minimal surface defects. The experimental component was operated in the Advanced Optical Lab at University of Waterloo, validated the responsiveness of the TFLN waveguide to E-field variations emitted by antenna elements. Notable experimental findings included a recorded 2% reduction in the waveguide's output power following antenna E-field activation, which was slightly lower than the 5% decrease predicted by simulation models.

This 3% difference illustrates the challenges associated with applying theoretical models to practical implementations, highlighting the necessity for rigorous experimental validation. Further observations revealed that when the input power of antennas was maintained below 10 dBm, the power variance at the waveguide's output was less than 1%. This sensitivity to E-field fluctuations suggests that TFLN-MZI waveguides could effectively function as detectors for electromagnetic field variations, potentially serving as a valuable tool for synchronous diagnostics and calibration of antenna arrays.

In conclusion, this thesis proposes an innovative approach for E-field sensing with TFLN-based optical devices, specifically in the context of phased-array antennas. Through a synthesis of theoretical analysis, fabrication techniques, and empirical validation, the study advances the knowledge of integrating TFLN waveguides into antenna systems for enhanced diagnostics and calibration. The findings suggest paths for further research, particularly in optimizing the sensitivity and integration efficiency of TFLN-based optical devices for telecommunications and sensing applications.