Simple HUD optics design can be described with below image.
As you can see, if combiner and colimating lens(after fold mirror) aligned to the center, i think view point(eye pupil) can see colimating lens(after fold mirror) according to the re-reflecting rays by combiner(another expression mirror reflection).
Simple test with a couple Beam splitter as shown below image
As above, we can see colimating lens(small b.s) at the big b.s(combiner).
Here are my questions:
To avoid those problems, should the ray have to be tilt(combiner, source ray's incident angle) obliquely to avoid re-reflecting ray. I think using this solution is a normal way. how can I remove above problem(re-reflecting ray) in HUD optics?
it just idea, can I solve the problem with using polarization?(PBS or wave-plate)
i think it seems to look like this
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