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Proceedings Paper

Frequency-modulated laser ranging sensor with closed-loop control
Author(s): Fabian M. Müller; Gunnar Böttger; Christian Janeczka; Norbert Arndt-Staufenbiel; Henning Schröder; Martin Schneider-Ramelow
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Paper Abstract

Advances in autonomous driving and robotics are creating high demand for inexpensive and mass-producible distance sensors. A laser ranging system (Lidar), based on the frequency-modulated continuous-wave (FMCW) method is built in this work. The benefits of an FMCW Lidar system are the low-cost components and the performance in comparison to conventional time-of-flight Lidar systems. The basic system consists of a DFB laser diode (λ= 1308 nm) and an asymmetric fiber-coupled Mach-Zehnder interferometer with a fixed delay line in one arm. Linear tuning of the laser optical frequency via injection current modulation creates a beat signal at the interferometer output. The frequency of the beat signal is proportional to the optical path difference in the interferometer. Since the laser frequency-to-current response is non-linear, a closed-loop feed-back system is designed to improve the tuning linearity, and consequently the measurement resolution. For fast active control, an embedded system with FPGA is used, resulting in a nearly linear frequency tuning, realizing a narrow peak in the Fourier spectrum of the beat signal. For free-space measurements, a setup with two distinct interferometers is built. The fully fiber-coupled Mach-Zehnder reference interferometer is part of the feed-back loop system, while the other - a Michelson interferometer - has a free-space arm with collimator lens and reflective target. A resolution of 2:0 mm for a 560 mm distance is achieved. The results for varying target distances show high consistency and a linear relation to the measured beat-frequency.

Paper Details

Date Published: 22 February 2018
PDF: 6 pages
Proc. SPIE 10539, Photonic Instrumentation Engineering V, 1053909 (22 February 2018); doi: 10.1117/12.2289585
Show Author Affiliations
Fabian M. Müller, Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (Germany)
Karlsruhe Institute of Technology (Germany)
Gunnar Böttger, Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (Germany)
Christian Janeczka, Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (Germany)
Norbert Arndt-Staufenbiel, Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (Germany)
Henning Schröder, Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (Germany)
Martin Schneider-Ramelow, Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (Germany)


Published in SPIE Proceedings Vol. 10539:
Photonic Instrumentation Engineering V
Yakov G. Soskind, Editor(s)

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