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Emerging Imaging and Sensing Technologies for Security and Defence

Quantum lidar using stationary broadband light

Peng Kian Tan, Xi Jie Yeo, Li Jiong Shen, Christian Kurtsiefer

Published Sep 8, 2021• 1 citation
Publisher

Abstract

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.

DOI
10.1117/12.2593008

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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.
We demonstrate an optical ranging technique using stationary light implemented on a semiconductor laser diode operating below threshold, with the required time-of-flight information extracted from thermal photon bunching. In contrast, conventional ranging techniques require a light source to be timing modulated in intensity, phase, or frequency, with which to correlate the reference and probe-to-target beams. This reference-probe correlation provides for time-of-flight information from which the target distance can then be measured. Presently, quantum ranging schemes derive timing correlation information from spontaneous parametric down-conversion sources which need not be timing modulated [1] , [2] . However, such light sources are complex and expensive to construct.
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.
Single-photon light detection and ranging (LiDAR) is a key technology for depth imaging through complex environments. Despite recent advances, an open challenge is the ability to isolate the LiDAR signal from other spurious sources including background light and jamming signals. Here we show that a time-resolved coincidence scheme can address these challenges by exploiting spatiotemporal correlations between entangled photon pairs. We demonstrate that a photon-pair-based LiDAR can distill desired depth information in the presence of both synchronous and asynchronous spurious signals without prior knowledge of the scene and the target object. This result enables the development of robust and secure quantum LiDAR systems and paves the way to time-resolved quantum imaging applications.
Single-photon light detection and ranging (LiDAR) is a key technology for depth imaging through complex environments. Despite recent advances, an open challenge is the ability to isolate the LiDAR signal from other spurious sources including background light and jamming signals. Here we show that a time-resolved coincidence scheme can address these challenges by exploiting spatio-temporal correlations between entangled photon pairs. We demonstrate that a photon-pair-based LiDAR can distill desired depth information in the presence of both synchronous and asynchronous spurious signals without prior knowledge of the scene and the target object. This result enables the development of robust and secure quantum LiDAR systems and paves the way to time-resolved quantum imaging applications.
The range and speed of a moving object can be ascertained using the sensing technique known as light detection and ranging (LiDAR). It has recently been suggested that quantum LiDAR, which uses entangled states of light, can enhance the capabilities of LiDAR. Entangled pulsed light is used in prior quantum LiDAR approaches to assess both range and velocity at the same time using the pulses' time of flight and Doppler shift. The entangled pulsed light generation and detection, which are crucial for pulsed quantum LiDAR, are often inefficient. Here, we study a quantum LiDAR that operates on a frequency-modulated continuous wave (FMCW), as opposed to pulses. We first outline the design of the quantum FMCW LiDAR using entangled frequency-modulated photons in a Mach-Zehnder interferometer, and we demonstrate how it can increase accuracy and resolution for range and velocity measurements by n\sqrt{n}n​ and nnn, respectively, with nnn entangled photons. We also demonstrate that quantum FMCW LiDAR may perform simultaneous measurements of the range and velocity without the need for quantum pulsed compression, which is necessary in pulsed quantum LiDAR. Since the generation of entangled photons is the only inefficient nonlinear optical process needed, the quantum FMCW LiDAR is better suited for practical implementations. Additionally, most measurements in the quantum FMCW LiDAR can be carried out electronically by down-converting optical signal to microwave region.
Quantum lidar leverages the quantum properties of light to gain advantages over classical lidar, such as enhancing range accuracy and reducing the emitted optical power needed to detect a target. The low optical power makes quantum lidar especially attractive for minimizing the probability of being detected by an adversary. Various quantum sources have been considered for quantum lidar; however, a practical comparison between such widely different systems is challenging. Here, we develop a theoretical model tailored to quantum lidar for stealth ranging and imaging, and compare the performance of such systems using an attenuated pulsed laser, a quantum dot single-photon source, and a spontaneous parametric down-conversion correlated photon pair source. To ensure a fair comparison, all sources employ time correlations for detection and are equalized in terms of optical power and detectability by an adversary. Furthermore, we demonstrate the limitation of the signal-to-noise ratio (SNR) as a sole metric, as it ignores the acquisition time required to confidently identify a target. To address the limitation of SNR, we supplement this metric with receiver operating characteristic (ROC) curves. With the inclusion of ROC curves, we find that the pulsed laser and the quantum dot single-photon source outperform the correlated photon pair source when an adversary possesses a non-photon-number-resolving detector. In contrast, when facing a photon-number-resolving detector, the quantum dot single-photon source remains optimal while the correlated photon pair source outperforms the pulsed laser. Our findings demonstrate that the use of a correlated photon pair source for quantum lidar does not always outperform alternative sources with equal SNR and optical power. Finally, using ROC curves, we establish the practical range limitations of quantum lidar.