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

Optical Ranging using a Subthreshold Laser Diode

Peng Kian Tan, Christian Kurtsiefer

Published Jun 21, 2021• 0 citations
Publisher

Abstract

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.

DOI
10.1109/cleo/europe-eqec52157.2021.9542011

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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.
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.
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 this article, we demonstrate theoretically and experimentally how one can exploit correlations generated in monolithic semiconductor quantum light sources to enhance the performance of optical target detection. A prototype target detection protocol, the quantum time-correlation (QTC) detection protocol, with spontaneous parametric down-converted photon-pair sources, is discussed. The QTC protocol only requires time-resolved photon-counting detection, which is phase-insensitive and therefore suitable for optical target detection. As a comparison to the QTC detection protocol, we also consider a classical phase-insensitive target detection protocol based on intensity detection. We formulated the target detection problem as a probe light transmission estimation problem, and we quantify the target detection performance with the Fisher information criterion and the receiver operation characteristic analysis. Unlike classical target detection and ranging protocols, the probe photons in our QTC detection protocol are completely indistinguishable from the background noise and therefore useful for covert ranging applications. Finally, our technological platform is highly scalable and tunable and thus amenable to large scale integration necessary for practical applications.
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.
Semiconductor diode lasers have been widely used in atomic physics and quantum optics. Advanced semiconductor lasers have the capability of modulation in intensity or optical frequency at the rate greater than a few GHz by modulating the driving current. This characteristics makes semiconductor laser diodes ideal light sources in the study of optical coherent transient phenomena with the time scale ranging from few milliseconds to sub-nanoseconds. In this paper, we discuss the applications of semiconductor lasers in coherent transient measurements and report our experimental results.