SPONSORED CONTENT Illuminating lidar
Gemma Church examines how Synopsys’ LightTools illumination design software simulates complex automotive lidar systems
L
idar systems can help autonomous vehicles navigate the world’s road networks – but this is
no easy feat. Automotive lidar systems are not only complex entities in themselves but they must also interact with an equally complex and diverse world where the surrounding conditions vary greatly. Whether rain or shine, this
is where illumination software can help. It provides operators with the insights they need to understand how complex lidar systems will perform under such variable conditions. To achieve this, there are many
challenges to face, including the fact that the lidar system itself is difficult to simulate. Dr Jake Jacobsen, technical marketing manager of the Optical Solutions Group at Synopsys, explained: ‘Lidar systems in general are complex electro-mechanical devices. They typically have a moving body, possibly with additional moving parts inside the housing.’ Jacobsen added: ‘This is coupled with the timing mechanisms to give the ranging feedback necessary. The return signal is generally weak, especially for more distant targets, so you have to consider stray light, background illumination from the sun and atmospheric effects. Couple this with the variation in target surfaces and you have a very interesting problem when trying to predict signal strength.’ In fact, there are a vast range
of interconnected variables to consider when selecting the best lidar system components. ‘Other interesting issues involve the size, shape and divergence and power of the laser beam as it emerges from the lidar system. This will depend on
22 Electro Optics June 2020
the particulars of the laser source and the expansion and transmission system in use. These problems involve tradeoffs between beam size, device size, beam divergence and system resolution. The engineer will need to use a package such as LightTools to determine the optical layout necessary to get the desired system performance,’ Jacobsen explained. The LightTools illumination design software from Synopsys can deal with complex, 3D objects, either developed using native geometry tools or imported from a CAD system. It is an easy- to-use system, which is more than capable of dealing with the complexities of simulating the optical performance of automotive-based lidar systems. Once the basic lidar system
simulation is set up, the designer can optimise that system, moving the target or altering other factors to understand the impact of system performance. This can
“Once the basic lidar system simulation is set up, the designer can optimise that system, moving the target or altering other factors”
help designers decide on the type of laser source or detector array, for example, or the impact of changing the detector filter on the background light readings. Jacobsen explained:
‘LightTools allows you to build up the system in a realistic way, and then build the world around the system for the light to interact with. You can then launch light from your system, into the world and back again to your detector.
Figure 1. Cutaway diagram of the test lidar system
Figure 2. Lidar system shown illuminating a target cube at 25m distance
You can also add in external sources such as the sun and look at the returns expected from those sources.’ ‘But maybe more importantly
than modelling the expected return, the designer can use the built-in analysis tools of LightTools to analyse what is going on inside the system,’ Jacobsen added. Using this software system,
the design team can answer questions that might be ‘difficult, time consuming or even impossible to answer with a prototype,’ according to Jacobsen. For example, the designers could locate system losses, understand beam overlaps between adjacent pulses, identify the root causes behind strange signal phenomena, and so on.
Real-world dilemmas ‘Modelling the external world is another issue altogether,’ according to Jacobsen. ‘The real world is endlessly varied. So, the question the designer must consider is what kinds of targets and situations need to be modeled to gain sufficient understanding of the expected performance in the real world.’ Typically, a selection of surfaces is measured in the
laboratory to understand their scattering properties. This information is then directly imported into LightTools, along with models of different vehicle geometries and environmental conditions, such as the location of the sun and possible obstructions in the road and surrounding area. Jacobsen explained: ‘The designer’s job is to select the important situations out of the infinite variety to give confidence in the system performance for the infinite other situations that were not modeled.’ In a recent whitepaper,
Synopsys explores the effects on the expected return signal of scattering properties, incidence angles, and atmospheric conditions for a typical automotive lidar system, using its LightTools illumination design software system. This work highlighted several benefits of this illumination software solution when tackling such complex lidar systems and their surroundings. For starters, the Parametric Controls in LightTools allow users to set up a collection of numeric parameters and equations which can be used to easily drive the geometry, adjust filter settings, and change just about anything in the model.
@electrooptics |
www.electrooptics.com
Synopsys
Synopsys
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