This is the second of three articles introducing the concept of k-space and discussing how to plan for an exit pupil expander design.

The role of augmented reality in medical applications is growing. One area of note: The run-of-the-mill blood draw.

For those with veins that collapse or are hard to locate, getting blood drawn for a cholesterol test or annual physical scan can be painful and frustrating. Fortunately, advancements in augmented reality (AR) can make the experience a little less tense. With an AR device, blood stands out on infrared overlay, making it easier for the phlebotomist to know where to aim for the vein. This makes the process quicker and much more accurate, vastly improving patient comfort.

In this article we will discuss how the exit pupil expander (EPE) with diffractive optics works in OpticStudio. This is Part 2 of a three-part series. If you missed Part 1, you will find it here.

Precise imaging is imperative for the design and development of an AR device. Gratings are a key optical element that separates light into wavelengths or colors, helping to produce an accurate virtual environment for the end user. In this article, we will continue with the set-up of an exit pupil expander (EPE) using the RCWA tool for an augmented reality (AR) system in OpticStudio, discussing the waveguide and three gratings that were used in our process:

1.  Waveguide and first (in-coupling) grating - The first step is to set up the waveguide and first grating as shown in Figure 1.​​  

   

    Figure 1 Waveguide and first grating.                                

2. Second (turning) grating - In the second step, a turning grating is added. This grating expands the incident beam in one direction and turns its propagation direction by 90 degrees. 
   

   Figure 6 A turning grating added to the system.                      

3. Third (out-coupling) grating and detector - The final step is to add the third grating and a detector to detect the out-coupled light. When rays hit the third grating, they split. Part of energy goes to diffraction order +1 and leaves the waveguide. Another part of the energy keeps going in the same direction, which is the zero order. 
   

   Figure 9 Exit pupil expander with 3 gratings.

In Part 3 of this series, we will complete the set-up, discussing how to check the footprint diagram and simulate the image for the EPE system. We will also touch on points for designers to consider when creating their own system.

To learn more, Zemax customers can access the entirety of this Knowledgebase article and the entire series on MyZemax.com. Otherwise, please reach out to Zemax Sales to learn more about OpticStudio.

Author: 

Michael Cheng
Senior Optical Engineer
Zemax