Theses Doctoral

Visible to near-infrared integrated photonics light projection systems

Shin, Min Chul

Silicon photonics is leading the advent of very-large-scale photonic integrated circuits (PICs) in which lasers, modulators, photodetectors, and multiplexers are integrated on a single chip and synchronized to enable faster data transfer both between and within highly integrated chips. Silicon photonics now extends beyond communication applications, paving new paths for many emerging applications and holding great potential in creating a compact beam projector.

Compact beam steering in the visible and near-infrared spectral range is required for emerging applications such as augmented reality (AR) and virtual reality (VR) displays, optical traps for quantum information processing, biosensing, light detection and ranging (LiDAR), and free-space optical communications (FSO). Here we discuss two novel integrated beam steering platforms in the visible and near-infrared wavelengths, optical phased array (OPA) and focal plane switch array (FPSA), that can shape and steer a light beam.

Previous OPA demonstrations have been mainly limited to the near-infrared spectral range due to the fabrication and material challenges imposed by the smaller wavelengths. Here we present the first active blue light phased array at the wavelength of 488 nm, leveraging a high confinement silicon nitride (Si₃N₄) platform. We randomly and sparsely place the emitters to remove grating lobes, alleviate fabrication constraints at this short wavelength and achieve a wide-angle 1D beam steering over a 50° field of view (FoV) with a full width at half maximum (FWHM) beam size of 0.17°. This demonstration is a crucial first step in realizing a non-mechanical fully-integrated beam steering device for many emerging applications.

Unlike 1D steering OPA, designing 2D OPA impose a different challenge. Numerous issues arise, including complicated waveguide routing and optical crosstalk between channels. Also, creating a highly directional beam without ghost images is required to deploy visible OPAs in emerging applications. However, current demonstrations of visible OPAs, including our first demonstration, suffer from the issue of low directionality due to the presence of grating lobes, high background noise and a low percentage of power in the main beam. We demonstrate an integrated OPA that generates a highly directional beam at blue wavelengths (488 nm) by leveraging a disordered hyperuniform distribution of emitters. This exotic distribution is found in birds’ cone photoreceptor arrangements, the most uniform sampling given intrinsic packing constraints. Such unique distribution allows us to mitigate fabrication and waveguide routing constraints and achieve a beam with low background noise, high percentage of power and no grating lobes. Large-scale integration of the platform enables fully reconfigurable high-efficiency light projection across the entire visible spectrum. The novel platform offers a viable platform for next-generation applications in visible-spectrum addressing, imaging, and scanning displays.

Although OPA is an invaluable device for creating a highly directional beam on a chip-scale, OPA has an inherent power consumption issue. Its architecture requires simultaneous control of all the phase shifters in the system for operation. We propose a novel silicon photonics FPSA system for beam steering with orders of magnitude lower electrical power consumption than other state-of-the-art platforms. The demonstrated system operates in the near-infrared wavelength regime; however, this can be extended into different wavelengths. Our demonstration enables low-size, weight, and power (SWaP) LiDAR for precision and autonomous robotics and optical scanners for mobile devices.


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More About This Work

Academic Units
Electrical Engineering
Thesis Advisors
Lipson, Michal
Ph.D., Columbia University
Published Here
October 12, 2022