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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Coherent Two-Photon LIDAR with Incoherent Thermal Light

Chung-Hyun Lee, Yosep Kim, Dong-Gil Im, U-Shin Kim, Vincenzo Tamma, Yoon-Ho Kim

Published Jun 26, 2023• 0 citations
Publisher

Abstract

The counterintuitive emergence of second-order interference beyond the coherence length has been observed and reported in quantum optical systems [1], [2]. This phenomenon can lead to potential remote sensing applications by overcoming the key limitation of the coherent LIDAR (Light Detection and Ranging), such as the source coherence length, which defines the maximum detection range. In this work, we present an experimental demonstration of coherent two-photon LIDAR beyond the coherence length with thermal light.

DOI
10.1109/cleo/europe-eqec57999.2023.10231901

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The counterintuitive emergence of second-order interference beyond the coherence length has been observed and reported in quantum optical systems [1], [2]. This phenomenon can lead to potential remote sensing applications by overcoming the key limitation of the coherent LIDAR (Light Detection and Ranging), such as the source coherence length, which defines the maximum detection range. In this work, we present an experimental demonstration of coherent two-photon LIDAR beyond the coherence length with thermal light.
Coherent light detection and ranging (LIDAR) offers exceptional sensitivity and precision in measuring the distance of remote objects by employing first-order interference. However, the ranging capability of coherent LIDAR is principally constrained by the coherence time of the light source determined by the spectral bandwidth. Here, we introduce coherent two-photon LIDAR, which eliminates the range limitation of coherent LIDAR due to the coherence time. Our scheme capitalizes on the counterintuitive phenomenon of two-photon interference of thermal light, in which the second-order interference fringe remains impervious to the short coherence time of the light source determined by the spectral bandwidth. By combining this feature with transverse two-photon interference of thermal light, we demonstrate distance ranging beyond the coherence time without relying on time-domain interference fringes. Moreover, we show that our coherent two-photon LIDAR scheme is robust to turbulence and ambient noise. This work opens up novel applications of two-photon correlation in classical light.
It has recently been shown that counter-intuitive Franson-like second-order interference can be observed with a pair of classically correlated pseudo thermal light beams and two separate unbalanced interferometers (UIs): the second-order interference visibility remains fixed at 1/3 even though the path length difference in each UI is increased significantly beyond the coherence length of the pseudo thermal light [Phys. Rev. Lett.119, 223603 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.223603]. However, as the pseudo thermal beam itself originated from a long-coherence laser (and by using a rotating ground disk), there exists the possibility of a classical theoretical model to account for second-order interference beyond the coherence time on the long coherence time of the original laser beam. In this work, we experimentally explore this counter-intuitive phenomenon with a true thermal photon source generated via quantum thermalization, i.e., obtaining a mixed state from a pure two-photon entangled state. This experiment not only demonstrates the unique second-order coherence properties of thermal light clearly but may also open up remote sensing applications based on such effects.
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.
Abstract A novel thermal light interferometer was recently introduced by Tamma and Seiler (2016 New J. Phys. 18 032002). Here, two classically correlated beams, obtained by beam splitting a thermal light beam, propagate through two unbalanced Mach–Zehnder interferometers. Remarkably, second-order interference between the long and the short paths in the two interferometers was predicted independently of how far, in principle, the length difference between the long and short paths is beyond the coherence length of the source. This phenomenon seems to contradict our common understanding of second-order coherence. We provide here a simple description of the physics underlying this effect in terms of two-photon interference.
We report the observation of a counterintuitive phenomenon in multipath correlation interferometry with thermal light. The intensity correlation between the outputs of two unbalanced Mach-Zehnder interferometers (UMZIs) with two classically correlated beams of thermal light at the input exhibits genuine second-order interference with the visibility of 1/3. Surprisingly, the second-order interference does not degrade at all no matter how much the path length difference in each UMZI is increased beyond the coherence length of the thermal light. Moreover, the second-order interference is dependent on the difference of the UMZI phases. These results differ substantially from those of the entangled-photon Franson interferometer, which exhibits two-photon interference dependent on the sum of the UMZI phases and the interference vanishes as the path length difference in each UMZI exceeds the coherence length of the pump laser. Our work offers deeper insight into the interplay between interference and coherence in multiphoton interferometry.
We report an experimental demonstration for a counter-intuitive phenomenon in multi-path interferometer with thermal light. The intensity correlation between the outputs of two unbalanced Mach-Zehnder interferometers (UMZIs) with two correlated beams of thermal light at the input exhibits genuine second-order interference with the visibility of 1/3. Here, the second-order interference does not degrade at all no matter how much the path length difference in each UMZI is increased beyond the coherence length of the thermal light.