J. Eur. Opt. Society-Rapid Publ. 2026, 22, 40 Ó The Author( s), published by EDP Sciences, 2026 https:// doi. org / 10.1051 / jeos / 2026019 Available online at: https:// jeos. edpsciences. org
EOSAM 2025 Guest editors: Omar El Gawhary, Stefan Witte, Ignacio Moreno
Journal of the European Optical Society-Rapid Publications
RESEARCH ARTICLE
Eye-safe non-line-of-sight localization using compact nanosecond laser diodes and single-photon-avalanche-diode arrays
Konstantin Albert 1, 2,*, Julian Klein 1, Manuel Ligges 1, and Anton Grabmaier 1, 2
1 Fraunhofer Institute for Microelectronic Circuits and Systems, 47057 Duisburg, Germany 2 University of Duisburg-Essen, 47057 Duisburg, Germany
Received 26 November 2025 / Accepted 24 February 2026
Abstract. Active optical non-line-of-sight( NLOS) imaging faces severe photon loss and stringent timing demand, often motivating bulky, non-eye-safe systems with femto- or picosecond lasers and spatial scanning schemes. We present an eye-safe, compact NLOS localization approach that uses a single-photon-avalanchediode array with on-chip timing and inexpensive and compact nanosecond pulsed laser diodes. To circumvent first-photon induced saturation in soft-gated detectors, the scene is illuminated from two positions placed outside the detector’ s field of view. The detector observes the relay wall in parallel, yielding a photon-efficient, nonconfocal measurement. Transient simulation of multiple scattered laser pulses, that returned to the relay wall after an object interaction, are used with back projection reconstruction to assess illumination schemes. It is shown that superimposing reconstructions from two non-central illumination positions reduces the pulsewidth-induced uncertainty of the determined target position, which is validated by measurements. Further compensation of the extended pulse width is analyzed with temporal and spatial filters. Matched filtering in the temporal domain outperforms spatial edge detection in the reconstruction volume, so that localization resolution becomes primarily limited by the detector’ s temporal resolution and measurement geometries rather than temporal pulse width. We outline a hybrid LiDAR-NLOS system for direct relay-wall calibration, pointing toward practical, eye-safe NLOS localization, with compact solid-state hardware.
Keywords: Non-line-of-sight, Eye-safe, Localization, Single-photon-avalanche-diode.
1 Introduction
Most environmental sensing systems, i. e. radar, light detection and ranging( LiDAR), ultrasonic sensors or conventional cameras are designed to observe a scene in direct line of sight. The measured area or volume of interest varies substantially, spanning from single-point intensity measurements to spatially resolved, three-dimensional information. When the observing systems cannot be positioned to view the scene of interest directly, systems based on non-lineof-sight( NLOS) approaches might be used. Potential applications for such approaches include collision avoidance in automotive and robotic contexts, locating people behind doors or rubble for public safety and rescue, and industrial inspection of occluded defects. Although NLOS systems can employ various remote sensing modalities [ 1 – 4 ], time-correlated photon-based approaches have been the main focus of research to date [ 5 – 10 ]. They exploit diffuse reflections from everyday surfaces and afford discrete illumination positions
* Corresponding author: konstantin. albert @ stud. uni-due. de and high temporal resolution, which are crucial for highresolution reconstruction of hidden scenes [ 9 ].
Active optical NLOS imaging refers to measuring multiple scattered laser pulses to extract information about scene elements that are not directly visible to the observer. The system typically comprises a collimated pulsed laser and a detector with high temporal resolution, which together illuminate and observe multiple positions on a relay wall positioned in the direct line of sight. The pulse scatters off the relay wall into the NLOS scene, where it undergoes secondary scattering from objects hidden in the scene and the rebounds back to the relay wall, where it can be observed directly by an optical detector( see Fig. 1a). The resulting multiply scattered transients on the relay wall are measured with spatial and temporal resolution. Such optical NLOS systems are differentiated by the arrangement of illumination and detection points. Confocal arrangements [ 8, 10 – 12 ] scan the relay wall and measure transients only at the current illumination point, ignoring most returning reflections and thus being inherently photon-inefficient. In contrast, non-confocal arrangements, with arbitrary numbers and positions of illumination and
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