Dear Experts,

I have an optical system entering through two optical wedges (9deg wedge angle) and going through some focusing optics coupling into a SM fiber. I use the wedges for beam deflection. With a coordinate break I make sure to get the beam to the single mode fiber. I have several configurations to simulate different angle (0deg to 57deg).

With the fiber coupling window I can see the fiber coupling efficiency. From the plots you can see that mainly the first surface of the first wedge causes significant vignetting, which is in addition depending on the angle. At larger angles the aperture of the wedge becomes effectively elliptic, shrinking the short axis with the cosine of the angle. Therefore, also the System Efficiency should drop with the cosine of the angle.

31.5mm the radius of the wedge, 50mm the radius of the aperture. First one at 0deg, second one at 57deg. I added 0.8 to roughly model the Receiver Efficiency:

>> 31.5^2*cos(0/180*pi)/50^2*0.8

ans = 0.31752

>> 31.5^2*cos(57/180*pi)/50^2*0.8

ans = 0.17293

Below the 3D layout I show the two output results of fiber coupling in Zemax.

Somehow, these values don’t match with my own octave calculation, which should read 0.31 to 0.17.

Somehow, I don’t get the difference in the calculations. Of course, little difference will be OK, because there will be also some minor other vignetting effects in the system, but my result is 50% loss between 0/57deg, while Zemax shows only ~6% loss between those angle.

Maybe somebody has a hint for me.

Many thanks

Markus