Specifically what problem are you having? Please describe it in detail and if possible attach the design in Zemax Archive (.ZAR) format. 


Best regards,

David 

Thanks David. I am trying to simulate this setup of fiber coupling : Single-mode fiber coupling in OpticStudio · MyZemax with a real lens from thorlabs with 2.97 mm focal lenght. I cant attach ZAR file but you can see in above link the file. 

The problem is how to simulate it with real lenses. I am not getting a collimated beam when I put the lens at 2.97 mm from the fiber. Its really strange.

Hello Hafeez,

In the Knowledge Base article you link to, notice that the object/lens and lens/image distances were set by hand initially to approximate values, but then later finally determined by optimization. The reason for this is that the distance from a real lens to the focal point is measured from an ideal surface called the principal plane. (Google this!) This is a theoretical surface which does not correspond to the apex of the first or last surface. So in your case, while the lens has a focal length of 2.97mm, that is not the distance from the fiber to the first surface of the lens.

In the spec sheet for the lens you are using you will find a specification for the working distance (WD) of 1.31mm. This would be the distance from the focal point to the first lens surface. (Actually lens surface to laser window, but close enough.) But it should be considered approximate for fiber coupling. I suggest that you use this distance in place of the 0.1mm used in the article, and proceed through your design using your lenses, by following the article step by step.

Kind regards,

David