[Webinar] Modeling Flash Lidar in OpticStudio, Part 2: Lidar Simulation in Non-Sequential Mode [Q&A]

@bspokoyny 

Q: When using importance sampling, is the power reaching the detector actually meaningful? Or is it artifically "high"?

A: Importance Sampling is a method for sampling scattered rays from a surface scatter definition, which takes into account the actual scattering profile defined on the surface. It improves the signal that the target object receives (the target which you are “aiming” scattered rays at) by having OpticStudio selectively trace rays within a cone originating on the scatter location which will subtend the scatter target. The power of these scattered rays will be attenuated to match the power contained in that specific solid angle of the BSDF/other scatter profile you have on the surface.

The main detail to keep in mind is that while OpticStudio will use the scatter profile defined on the surface, all scattered rays carry the same flux within the scattering solid angle, as it will take the average power within that solid angle. So it’s best suited for scatter profiles where the range of scattered ray vectors measured from the surface normal (shown on the plot below as the region between vertical red bars) does not have a rapidly changing scatter function or if it’s an adequate approximation to take the average scatter function value within that range of scatter vectors. The average scatter function value is shown as the horizontal red line in the chart below:

For more information, feel free to take a look at the article here: How to use importance sampling to model scattering efficiently – Knowledgebase (zemax.com)

Q: In the more enhanced image Angel showed, there were dark grid marks on the image that were not present in the scene.  What made those marks?

A: Just to make sure, you were referring to this part of the presentation?:

This is coming from the size of my extended source and the diffraction angle from my “2D grating” (the crossed linear grating objects). I just didn’t size my source large enough to have overlaps in the boundaries from the diffraction angle, so these gaps could be quickly filled in by adjusting the grating’s period or by making the source larger.

@Hui.Chen 

Q: does ZOS calculate optical path length of each individual ray?

A: Yes, OpticStudio keeps track of the optical path length of each ray in both sequential and non-sequential tracing modes. This path length tracking is what enables the API solution used in this webinar – you can read more about the Time-of-Flight User Analysis here: How to create a Time-Of-Flight User Analysis using ZOS-API – Knowledgebase (zemax.com)

@madeleine.akeson_01 

Q: Will the Lumerical solver be included in all OpticsStudio versions? Where can I find the webinar about the Lumerical solver DLL?

A: The Lumerical solver is separate software that you will need a license to run. By running the Diffractive DLL in OpticStudio which connects to Lumerical, it will look for a valid Lumerical license to finish the calculation. So it would be a separate procurement to OpticStudio.

For some more information, here is the webinar for the RCWA dynamic link functionality: [Webinar] AR waveguide design and optimization based on dynamic linking between Zemax OpticStudio and Lumerical RCWA [Q&A] | Zemax Community

@Mansour Das. 

Q: whats is the advantage of the NSM to the sequential design?

A: Defining such a system in sequential versus NS mode really comes down to the particular part of the design process you are in. Sequential Mode will be best used for measuring image quality of your respective systems, and you could also do a fair bit of optimization for the shape of the output beam using a method like described here: How to design a Gaussian to Top Hat beam shaper – Knowledgebase (zemax.com)

Non-Sequential Mode would be better suited for more thorough stray light analysis, incorporating housing of the lidar to gauge your system performance, and also to use enhanced functionality, such as the Time-of-Flight User Analysis or upcoming RCWA link as mentioned in this webinar.

Q: How is spatial information in x,y, and z extracted?

A: In non-sequential ray tracing, you can save the executed ray trace in full detail as a Ray Database File (.ZRD extension). This includes global XYZ intercepts on all objects a ray interacted with, the path length of the ray segment, direction cosines of propagation, and so on. So, you can use the .ZRD file to extract this information if you’re post-processing the ray database information (I already linked to it above, but here’s that time-of-flight article again for convenience 😊).

Q: Does the system form 3-D images from return signal? And how does it handle interference from different objects in field of view?

A: The depth information shown in the Time-of-Flight user analysis is obtained by calculating the total path length of each ray segment landing on your specified detector. OpticStudio is not natively generating 3D images, but the demonstration shows how you can leverage existing data to compute desired results. As for different objects in the field of view, at this time, the demonstration User Analysis will report the average of the path lengths hitting the pixel, so it would change the reported distance depending on the number of rays that are coming from the different objects in the scene.

Q: Can you calculate maximum range and spatial resolution of the LIDAR?

A: We covered this question a bit in the Part 1 thread, but the long story short is that while we did not calculate the maximum range of this lidar, this is certainly something you could set up to further characterize the model, as you can directly specify the input power of your sources, define the reflectance for various objects in the scene, as well as generate for yourself the ratio of some incident beam’s area on your scene to an object that will scatter/reflect the beam. It would have the added benefit to considering any losses from optical coatings or absorption of the lenses themselves, if you have absorption data defined for those materials.

@Yisi.Liu 

Q: when will you post this video and the part 1, and the previous webinar "Cell Phone Lens: The Fundamentals Behind the Optical System Design"?

A: Please see above for Parts 1 and 2 for this webinar series! As for the other webinar you mentioned, you can access that on-demand recording here: [Webinar] Cell Phone Lens: The Fundamentals Behind the Optical System Design [Q&A] | Zemax Community