Sequential vs Non-Sequential mode?

  • 11 February 2019
  • 5 replies

Userlevel 6
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What's the difference between Sequential and Non-Sequential Mode? When should I use one over the other?


Best answer by Allie 11 February 2019, 18:44

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5 replies

Userlevel 6
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In Sequential Mode, rays are traced from one surface to another in the sequence the surfaces are defined in the Lens Data Editor. Sequential Mode is limited to tracing a single transmission or reflection path for each ray, depending on whether a refractive or reflective element is used. While Sequential Mode is suitable when analyzing the performance of imaging and afocal systems, it is not suitable for illumination systems or systems where stray light and scattering is important.

Non-Sequential Mode is optimal for analyzing stray light, scattering, and illumination. In this mode, sources, objects and detectors are encountered in the order that the rays physically interact with the Objects after being emitted by a source. The rays may interact with Objects multiple times or not at all. At each interface, a parent ray may split into multiple child rays which are either transmitted, reflected, absorbed or scattered.

For more information, check out the Knowledgebase article "Exploring Non-Sequential Mode in OpticStudio".

It sounds like Non-Sequential Mode is more rigorous in all cases. Why would you ever not use it? Execution speed?

You need to do a better job of explaining the trade-offs here.
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Hi Daniel, 

Non-sequential ray tracing can generally be considered a more rigorous geometrical ray tracing method. This is because it allows for the consideration of ray scattering and splitting so that the user can get a more complete picture of how light will propagate in both expected and unexpected ways through the optical (or opto-mechanical) system. As Allie suggests, this is of critical importance of illumination system design and stray light analysis. 

That said, its rigor does not necessarily mean that Non-Sequential Mode is always the best choice for a design environment. With this rigor comes computational load, which ties directly to execution speed, as you suggest. Non-sequential calculations are generally much slower than their sequential counterparts.

The reason for this boils down to the fact that Sequential Mode greatly restricts the regions in which rays can propagate (i.e. from one defined surface exactly one other defined surface). This restriction allows Sequential Mode to make many assumptions about the optical system which both greatly increase computational efficiency and allow for different types of analyses. For example, limiting Sequential Mode to only one object plane with a defined system stop allows us to calculate and leverage the system's first-order properties. These first order properties subsequently form the basis for several analysis features, such as the Wavefront Map and FFT PSF, which are both of critical importance in many imaging systems. 

The big limitation of Sequential Mode, though, is that rays must follow a clearly defined path; that is, you need to know where you want light to go and generally how to get it there before you start the design. With this, light can also only interact with the optical surfaces of lenses, so you can consider the results to be "idealized," in the sense that you haven't yet considered other objects/surfaces with which light could interact. Non-Sequential Mode, on the other hand, is perfectly situated to model how light interacts with those "other" objects/surfaces, and it doesn't require you to define the intended path beforehand. This makes your life much easier when trying to model extended sources, for example, as it allows you to model the unpredictable interactions between rays and the physical geometry of those sources. 

Let me know if you have any other questions or comments here. 



Hii all,

Is there anyway to find the aberrations by using Non-sequential mode. Any response will be appreciable.





How can we study the aberrations in the non-sequential mode?