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Period- and Branch-Calibrated TI-PLM Holography for Selective Industrial LiDAR

Adnan Asghar1, Noah Oliver1
1University of Alberta, Edmonton, Canada

Abstract

Non-mechanical compact beam steering is essential for industrial LiDAR, robotic inspection, optical metrology, and safety monitoring because in most cases, the applications require illumination of specific regions and not a raster scanning over the whole scene with uniform resolution. The Texas Instruments phase light modulator (TI-PLM) provides a solution to the problem via a MEMS-based holographic steering based on phase only. However, the TI-PLM controller is forced to operate on a grid of mirrors, 10.8 μm pixel pitch, and 16 nonlinear phase states instead of a continuous phase ramp. In this research, we consider the reliability of multi-region steering using the TI-PLM controlled by a command protocol that depends on a calibration table containing information about the period-dependent loss of efficiency, phase-mismatch sensitivity due to rotation, and different diffraction power between two regions of interest. The quantitative calibration information includes weak periods of normalized diffraction efficiency at r = 3, 5.5, 6.5, and 7.5, the recovery of diffraction efficiency to 0.42 from 0.37 due to small in-plane rotation at r = 3, and diffraction efficiencies of two regions in symmetric and asymmetric hologram configurations. For a particular command, the steering request can be sent to the device unmodified, rotated, weighted by the branching parameter, or time-separated depending on the diffraction efficiency difference. The analysis demonstrates that the rotation-sensitive r = 3 period provides a 13.5% relative recovery without any hardware changes. Asymmetric two-region steering commands should incorporate amplitude buffer of 17.1% and 20.8% at a weak-branch condition in case of complex-field addition. Therefore, the TI-PLM guidance scheme is appropriate for the use in multi-regional industries LiDAR systems only if the issue of beam positioning is considered a control process, not a geometrical mapping from the required angle to the hologram period.

Keywords: TI-PLM; MEMS phase light modulator; LiDAR; computer-generated holography; beam steering; diffraction efficiency; industrial sensing; region-of-interest illumination; smart manufacturing; optical calibration
Citation
Adnan Asghar, Noah Oliver. Period- and Branch-Calibrated TI-PLM Holography for Selective Industrial LiDAR[J], TK Techforum Journal (ThyssenKrupp Techforum), Volume 2022 (3). 58-75.

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1Mechanical Engineering Department, Kuwait University, P. O. Box: 5969, Safat, 13060, Kuwait
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1Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA