Adding boundaries to connect with the Polarizing Beamsplitter

Posted 23.07.2026, 07:18 GMT-4 Electromagnetics, Wave Optics, Simulation Apps Version 6.3 1 Reply

Aadittya Tiwari

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Hello,

I want to use the Polarizing Beamsplitter (PBS), (Application ID: 31041), within a larger system, so I am attempting to add an air boundary (just a rectangle with n=1) to the right of the PBS, but I am getting the result shown in this image link: imglink.cc/i/fkkT6h7BNT

As far as I can tell, in order to create a new domain I need to define the wavevectors in that domain and a phase shift to ensure phase continuity between domains. The wavevector would just be lambda/n_air and the phase shift I calculate using the ODEs that calculated all the prior phase shifts within the PBS, using the new wavevectors I've created. However, I am getting a result that clearly has some noisiness to it and indicates that something is not right. When I change the refractive index of the domain from 1 to 1.6586, the exact refractice index of the adjacent prism, everything works fine and results in the clean image shown: imglink.cc/cdn/ntutmapbAC.png

Changing it from 1 to 1.6585, just 0.0001 less than the refractive index of the adjacent prism, leads to a result almost identical to the first noisy result when n=1. From this I'm assuming that I must be doing something wrong with the wavevectors, as that is the only quantity that would change by a large amount as a result of a tiny change in refractive index. But I have no idea what could be wrong there. Following are some relevant information of the changes I made to the file in order to implement an air domain:

Refractive Index of 'Right Air Domain' = n_air = 1 Interface between right prism and right air domain = x8 = width of PBS divided by 2 k1Airx = k0*n_air = k2Airy k1Airy = 0 = k2Airx k1Prismx*x8+phi180-k1Airx*x8-phiAirx k2Prismy*x8+phi200-k2Airy*x8-phiAiry phiAirx and phiAiry are used in the definitions section for the right air domain as phi1 and phi2 respectively.

I've uploaded my attempt at this after clearing all built meshes. If there are any questions about how I implemented anything I'm more than happy to respond. Thank you for your time!

Attachments:

extended_pbs.mph

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1 Reply Last Post 01.08.2026, 05:29 GMT-4

Aadittya Tiwari

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Posted: 3 hours ago

For anyone having this issue in the future, the issue is that you have to account for the reflections that arise when travelling 100% horizontally/vertically, the wave vectors can't represent them. The simplest solution is to create an antireflection coating between the two domains you want to connect using a Transition Boundary Condition, the refractive index of this coating would be the geometric mean of the two refractive indices you are connecting (here, 1.6586 and 1) and the thickness would be lambda/(4*n_antireflection) for the other. If you just made an actual domain with that thickness and refractive index you might be able to get the same result but might run into mesh issues trying to do something with the thickness of ~100nm.

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