# Ansys SPEOS: How to Create a Focusing Lens

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A common question we get asked is: can a focusing lens be created within Ansys SPEOS? And the answer is yes! And luckily, it’s pretty simple.

For this example, we will use an aspheric lens from Edmund Optics. The drawing provides all the optical parameters needed as inputs in SPEOS.

## Create the Lens in Ansys SPEOS

The lens will be created as a Projection Lens, which can be found in the design Tab of the ribbon bar in the Optical Part Design toolset.

The definition panel of the Projection Lens is where we can specify all the optical parameters. The z-axis was chosen as the optical axis of the lens to match the optical guidelines of ray propagation. The back focal length, lens thickness, and surface types are all found on the drawing of the lens. The orientation of the lens will follow the side view presented in the drawing. The construction parameters were left as the default settings.

The optical parameters of the back face were inserted from the drawing specifications. The curvature refers to the radius of curvature of the face. The definition panel contains the aspheric terms of each face. The aspheric terms correspond to the lettered terms provided in the aspheric sag equation in the drawing such that D in the drawing corresponds to the 2nd index in SPEOS, E corresponds to the fourth index, F to the 6th index, and so on.

Once all the parameters are defined, the lens should look like this:

Since we chose the back face to be the convex surface, the lens is 78.18 mm from the origin, which corresponds to the back focal length. But since the lens will be focusing collimated light to a point, the back focal length value defined does not matter for this example. If the light was diverging from a point source, then the lens would be rotated such that the plano face hits the incoming rays first. This configuration would make the back focal length a critical parameter.

## Define Material Properties in Ansys SPEOS

The next step is to define the material properties of the lens. Per the drawing, this lens is made of BK7 substrate, which is part of the Schott Catalog. Luckily for us, there is a Schott Catalog in the Optical Materials Library that contains material properties of BK7. The material file was copied from the Materials Libraries to the project input files. A new material was created and renamed “BK7 Glass.” The Volume Properties Type was set to Library and the material file for BK7 was chosen. The surface property was set to “Optical Polished.” The material was then applied to the lens.

## Simulate the Lens in Ansys SPEOS

Now the lens is all set-up, we can observe its focusing capabilities by having a collimated beam hit the lens and get focused to a point, corresponding to the focal length of the lens.

A detector was placed just past the focal length of the lens to observe the beam after focus. The collimated light has been transformed to a Gaussian Beam, as expected.

Now that we know how to create a lens in SPEOS, there is an even easier way that skips the Projection Lens creation altogether. Off-the-shelf manufacturers like Edmund Optics provide important files for their parts, like the drawing presented earlier in this post, the corresponding Zemax files, and the .STP files!

This means that all we would need to do is download the .STP file for this lens and import it into SPEOS. Once it is imported, all that is needed is to apply the same BK7 material properties as before. And voila! You’ve got your aspheric lens. Try it out with the Edmund Optics lense we used in this example.

We hope you find this useful. If you have any questions about Ansys SPEOS or any of the other Ansys optical simulation tools like Ansys Zemax OpticStudio or Ansys Lumerica, please contact us. Also, remember we can help with training, mentoring, and overflow simulation work.

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