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Frequency-modulated laser ranging sensor with closed-loop control

 
: Müller, F.M.; Böttger, G.; Janeczka, C.; Arndt-Staufenbiel, N.; Schröder, H.; Schneider-Ramelow, M.

:

Soskind, Y.G. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Photonic Instrumentation Engineering V : 30 January - 1 February 2018, San Francisco, California, United States
Bellingham, WA: SPIE, 2018 (Proceedings of SPIE 10539)
ISBN: 978-1-5106-1564-9
ISBN: 978-1-5106-1563-2
Paper 1053909, 6 pp.
Conference "Photonic Instrumentation Engineering" <5, 2018, San Francisco/Calif.>
Conference "Optoelectronics, Photonic Materials and Devices Conference" <2018, San Francisco/Calif.>
Photonics West Conference <2018, San Francisco/Calif.>
English
Conference Paper
Fraunhofer IZM ()

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.

: http://publica.fraunhofer.de/documents/N-520752.html