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Nature Communications

Thermal light with enhanced oscillating bunching in field-tested photon-counting LIDAR

Theodor Staffas, Jim Cleveborg, Jun Gao, Ali W. Elshaari, Val Zwiller

Published Dec 29, 2025• 0 citations
Publisher

Abstract

Abstract Traditional Light Detection and Ranging (LIDAR) systems rely on a modulated light source to encode information in the probe signal to measure distances. Alternatively, thermal LIDAR uses non-modulated thermal sources of bunched light. In this work, we demonstrate a bunched photon source at telecom wavelength, incorporated in a photon-counting LIDAR system, which determines distances by measuring the second-order correlation. The source is a sub-threshold laser spectrally filtered to extend coherence time, producing an oscillating g (2) curve with an enhanced bunching peak. Utilizing this oscillating bunching increases the signal-to-noise ratio and decreases the number of correlation events required to perform a measurement. This system achieves 2 ps resolution in both fiber-based and free-space measurements with up to 65 dB attenuation and ranges up to 87 km in optical fibers. Our approach demonstrates the possibility of increasing the bunching of classical light sources and improving their usability for LIDAR.

DOI
10.1038/s41467-025-67830-1

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Abstract Traditional Light Detection and Ranging (LIDAR) systems rely on a modulated light source to encode information in the probe signal to measure distances. Alternatively, thermal LIDAR uses non-modulated thermal sources of bunched light. In this work, we demonstrate a bunched photon source at telecom wavelength, incorporated in a photon-counting LIDAR system, which determines distances by measuring the second-order correlation. The source is a sub-threshold laser spectrally filtered to extend coherence time, producing an oscillating g (2) curve with an enhanced bunching peak. Utilizing this oscillating bunching increases the signal-to-noise ratio and decreases the number of correlation events required to perform a measurement. This system achieves 2 ps resolution in both fiber-based and free-space measurements with up to 65 dB attenuation and ranges up to 87 km in optical fibers. Our approach demonstrates the possibility of increasing the bunching of classical light sources and improving their usability for LIDAR.
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Conventional optical ranging techniques require timing modulated light sources to provide for the time-of-flight information, which may allow for detection, jamming or decoy by a third-party with information to the modulation pattern. Quantum ranging techniques, or quantum lidar, use spontaneous parametric down converted light sources to provide the timing correlation, where entanglement is not necessarily exploited in the simplementation, and is complex and expensive. Here we propose the use of stationary broadband light generated from a laser diode operating below threshold to provide the timing correlation, as extracted from thermal photon bunching.
Thermal light exhibits intensity fluctuations or photon bunching that has been used as a source of entropy or temporally correlated light. However, its low spectral density limits its use in practical applications like LIDAR. One method of remedying this is optical amplification to boost its brightness. In this paper, we show that the normalized second order coherence function g(2)(τ)g^{(2)}(τ)g(2)(τ) of a thermal light source is preserved after amplification. We then use amplified thermal light to demonstrate a LIDAR raster scan of a building at 1.3 km with a depth resolution of 2 cm.
This paper proposes a novel quantum lidar scheme based on the bunching effect of thermal light. By utilizing signal photons of the correlated photons via pulsed-pumped periodically poled lithium niobate (PPLN) waveguide, the system achieves a ranging precision of 156ps (corresponding to 4.7cm) with unambiguous distance measurement. Furthermore, by employing thermal light with the coherence time on the femtosecond scale, the ranging precision can be enhanced to the micrometer level. The proposed technique holds significant potential for applications in high-precision metrology, quantum imaging, and remote sensing, paving the way for future advancements in optical ranging technologies.
Classical sensing techniques such as range finding and clock synchronization use timing modulated light sources to provide the timing correlations needed for their implementation. Corresponding quantum schemes utilise spontaneous parametric down converted light sources to provide the timing correlations without the need for timing modulation, although entangled states are too fragile to be fully exploited presently. Here we demonstrate the use of thermal light as an alternative source for timing correlations, via the photon bunching generated from a laser operating below threshold, and showcase its practical viability by successful range finding measurements.
In order to enhance LIDAR performance metrics such as target detection sensitivity, noise resilience and ranging accuracy, we exploit the strong temporal correlation within the photon pairs generated in continuous-wave pumped semiconductor waveguides. The enhancement attained through the use of such non-classical sources is measured and compared to a corresponding target detection scheme based on simple photon-counting detection. The performances of both schemes are quantified by the estimation uncertainty and Fisher information of the probe photon transmission, which is a widely adopted sensing figure of merit. The target detection experiments are conducted with high probe channel loss (≃1−5×10−5\simeq 1-5\times10^{-5}≃1−5×10−5) and formidable environment noise up to 36 dB stronger than the detected probe power of 1.64×10−51.64\times 10^{-5}1.64×10−5 pW. The experimental result shows significant advantages offered by the enhanced scheme with up to 26.3 dB higher performance in terms of estimation uncertainty, which is equivalent to a reduction of target detection time by a factor of 430 or 146 (21.6 dB) times more resilience to noise. We also experimentally demonstrated ranging with these non-classical photon pairs generated with continuous-wave pump in the presence of strong noise and loss, achieving ≈\approx≈5 cm distance resolution that is limited by the temporal resolution of the detectors.