Max Julius Bode and Sarah Cwalina of the research group “Optical Metro, Access and In-House Networks” of the Photonic Networks department at the Fraunhofer Heinrich Hertz Institute (HHI) received the Best Paper Award at the IEEE International Workshop on Metrology for Automotive for their paper “Investigating Temperature Effects in Directly Modulated Laser-Diodes in Coherent FMCW-LiDAR Systems”. The event took place in Parma, Italy, and focused on the automotive sector - Dallara, the legendary motorsport manufacturer, presented the award.
LiDAR stands for “Light Detection and Ranging” and is a method of environmental detection. More precisely, the technology uses a laser source to create a 3D model from the captured environment. A distinction is made between various measuring principles such as “Time of Flight (ToF)” and “Frequency Modulated Continuous Wave (FMCW)”. The latter was used in the award-winning work.
More accurate and cheaper method
In FMCW-LiDAR, the continuous wave (CW) laser signal is modulated with a so-called frequency chirp. For distance measurement, the emitted signal, which is time-delayed by the distance to the target, is mixed with the signal without time delay (local oscillator signal). This results in a significantly lower intermediate frequency. The known modulation parameters of the frequency chip and the measured intermediate frequency are used to draw conclusions about the time delay and therefore also about the distance.
The aim of the project was to find out the temperature effects on the performance of LiDAR systems. The HHI researchers found that small fluctuations in the operating temperature of the semiconductor laser led to large errors in the lasing frequency and therefore in distance measurement. The prior characterization of the dynamic bandwidth of the lasers thus enables an efficient, novel compensation technique. This allows for omission of the temperature stabilization, thus increasing robustness and decreasing cost, making FMCW-LiDAR systems mor suitable for automotive applications.