Photonic integrated circuits for optical phased array beam steering and remote sensing based on heterodyne detection

Abstract

Photonic integration is a powerful technology for miniaturizing optical devices and systems. Being in the center of research interest for over two decades, photonic integration has made tremendous progress, driven primarily by the information industry's demand for high-bandwidth optical interconnects. However, its maturation has opened the door to new applications in recent years. Remote sensing and ranging applications have gained significant momentum as the next potential mass-market opportunity for photonic integrated circuits (PICs), particularly due to the automotive industry's growing interest in LiDAR. Many different technologies have spawn to address challenges related to high accuracy sensing and fast scanning and develop scalable and cost-effective solutions. Among the various existing integration platforms, silicon nitride (SiN) and polymer-based photonic integration are particularly interesting for remote sensing applications, primarily due to their low loss waveguides and passive components, their wide spectral range of operation, and the high-optical-power handling capabilities. This work leverages these platforms to develop two novel functionalities: optical frequency shifting (OFS) for heterodyne interferometry and two-dimensional laser-beam steering based on optical phased arrays (OPAs). OFS is based on stress-optic index modulation, that offers larger bandwidth than conventional thermo-optic phase shifters, by using lead zirconate titanate (PZT) thin films deposited on top of the SiN waveguides with a wafer-scale process. The OFS PICs are integrated into a NIR laser Doppler vibrometer (LDV) system for non-contact measurements of a vibrating surface. Furthermore, a process for hybrid integration of polymer waveguides on top of the SiN platform is introduced, to combine functionalities from both platforms in a fully compact manner. Optical phased arrays (OPAs) are implemented in the polymer-based technology platform, where multiple waveguiding layers are used to form rectangular apertures at the edge facet of the PICs. Two-dimensional (2D) steering of a NIR laser beam is demonstrated by individual phase control of each OPA channel using thermo-optic phase shifters. Linear aperiodic OPAs with non-uniform emitter spacing are explored to enhance the field of view and reduce control complexity. OPA characterization and calibration aspects are discussed, as well as fabrication considerations for multi-layer polymer PICs. Although the multi-waveguide-layer approach for 2D edge-emitting OPAs has been previously suggested, this work presents the first experimental demonstration of 2D beam steering based on this concept.