There are two distinct ray tracing modes supported by ZEMAX (Sequential and Non-Sequential), but often times it is necessary to combine the two techniques.   A design which uses both methods of ray tracing is often referred to as a “mixed-mode” system, a “hybrid” system, “non-sequential ray tracing with ports,” or mixed sequential/non-sequential mode.  The term “mixed-mode” is used most frequently.  The mode selection is found under the File menu from within ZEMAX:



Mixed mode systems contain one or more non-sequential object (called an NSC group) which is part of an otherwise sequential system.  An example might be a point or extended surface object which is represented by rays which follow a sequential ray path through one or more conventional lenses, then follow a non-sequential path through a prism or light pipe before illuminating the image surface.

This method of ray tracing requires the use of ports, namely the entry and exit ports, for rays to enter and leave each NSC group.  The entry and exit ports are a vital part of constructing a mixed mode system, and will be discussed in more detail in the following pages of this article.  When using ports, rays are launched from defined field positions on the OBJ surface.  All the usual sequential ZEMAX system data, such as field positions and pupil sizes, determine the properties of rays entering the NSC group. 

Rays enter the group through the entry port, and may only leave the group via the exit port; then continue through the remainder of the sequential system.

The diagram below highlights the progression of rays in a mixed mode design.  A collimated beam passes through the entry port and TIRs a few times from a 30-60-90 prism.  The collimated beam eventually hits the exit port, where the sequential ray trace is resumed, and the light is focused by an equiconvex lens.



So what’s the basic procedure for constructing a mixed mode system in ZEMAX?  Advance to the next page to find out more!