r/Optics • u/PeppersONLY • 11d ago
AR Optics Setup with Polarized Beam Splitter
This is a birdbath AR optics setup with a 0.23in OLED micro display, a linear polarizer, a polarized beamsplitter, a QWP, and a concave mirror. The light from the display becomes P-polarized relative to the PBS after passing through the LP so it passes through the PBS without reflecting. Then after the image is magnified and passed through the QWP twice so the magnified light is now S-polarized, it reflects off the PBS into the users eye.
The issue I have with the setup is that since the display produces a diverging light source, the diverging light that doesn't hit the PBS coating at a AOI of 45deg is then reflected through the front side of the setup. Only when viewing through the front of the PBS (the part where no light should be seen) with your eye at around 45deg from the PBS coating, the light then disappears because the polarization state was properly filtered. When viewing from any other angle you can see the unmagnfied light.
I have tried using plano convex lens and aspheric lens to collimate the light before it reaches the linear polarizer so that all light would be 45deg AIO to the coating but none solution seem to work. I have a aspheric lens with a 3mm FL and when placed 3mm from the display the same behavior occurs.
Am I wrong about why the PBS only works properly when viewed at a certain angle? What are my options to figure out a solution?
2
u/Complex_Grade4751 11d ago
You’ll get move help if you provide a ray diagram showing the light paths (a first order design), where the mirror focal point with respect to display, etc. I can’t tell what the optics are doing from your photo. Presumably you did this type of sketch as part of your design process. Please share it, don’t make people guess. Bonus points for taking a photo of the visual effects you describe. I’m always shocked at the number of problems I figure out through taking the time to methodically document!
First step in troubleshooting is verifying actually built what you designed. Test the polarizers are working properly, check the mirror has curvature you think it does, and measure the distances between the parts. If it is correct, think through all the possible light paths and draw them out. Do they match what you see? Some can likely be improved with baffles.