1. ECEN 4616/5616 Optoelectronic Design Class website with past lectures, various files, and assignments: http://ecee.colorado.edu/ecen4616/Spring2014/ To view video recordings of past lectures, go to: http://cuengineeringonline.colorado.edu and select “course login” from the upper right corner of the page. Lecture #34: 4/9/14

3. Non-Sequential Zemax Models We have been using Zemax in the Sequential mode – Every row in the Lens Data Editor defined a surface, and Zemax traces rays to these surfaces in the order in which they are in the editor. For example, here is a simple lens that we have adjusted the conic constant on to get perfect focusing of an on-axis beam through a glass plate:

4. Non-Sequential Zemax Models If we enter a negative distance between the components, such that their actual position is reversed: Rays are still traced through the surfaces in the order in which they appear in the LDE, not the actual order they are arranged in space:

5. Non-Sequential Zemax Models There are optical systems we would like to model, however, in which we can’t specify exactly which order all the rays will strike the surfaces – some rays may miss some surfaces entirely, while some may bounce multiple times from a single surface. An example of this would be a bent light pipe: “Torus Pipe.zmx” in the Zemax directory Samples\Non-sequential\Miscellaneous

6. Setting up Non-Sequential Zemax Models (Tips to avoid frustration) Let’s start with just a 5mm beam of rays passing through two surfaces and hitting the Image Plane: A pretty plain system.

7. Non-Sequential Zemax Models Let’s put a surface after the Stop and make it a Non-Sequential Component surface: Attempting a 2D layout gives us this error message:

8. Non-Sequential Zemax Models The 3D layouts still work fine: But, the NSC surface (note the smaller diameter in the LDE) appears a short distance in front of surface #3, even though we are not allowed to put a thickness in the LDE. The NSC “surface” doesn’t actually define a surface – it defines a pair of “Ports”: The “Entrance Port” where rays from the Sequential system enter the Non- Sequential system (defined in the NonSequential Editor), and the “Exit Port” where the rays exit the Non-Sequential system back into the rest of the sequential system. This is Zemax’s “Mixed-Mode”, or “NSC with Ports” (see Ch 12 in the Manual). The pure Non-Sequential Mode must be selected at startup from the ‘File’ menu: Select “File-Non-Sequential Mode”.

9. Non-Sequential Zemax Models The size of the Entrance Port is defined by the size of the NSC surface; The size of the Exit Port is defined by the size of the surface immediately following the NSC surface. Let’s make them both larger, so they stand out:

10. Non-Sequential Zemax Models The location of the Entrance port is the location of the NSC surface. The Exit Port location is determined by parameters on the NSC surface in the LDE: The ‘Exit Loc(ation) Z’ is 1 by default. If we change it to 10, the layout shows the Exit Port now 10 mm away from the Entrance Port: Note that there are 6 parameters to adjust the Exit Pupil location and orientation.

11. Non-Sequential Zemax Models The Exit Pupil acts like a Coordinate Break: Shifting it shifts the rest of the system by the same amount: And tilting it tilts the rest of the optical system:

12. Non-Sequential Zemax Models The “Draw Ports” parameter determines which ports will be shown in the layouts: 0: No ports 1: Entrance Port 2: Exit Port 3: All ports

13. Non-Sequential Zemax Models A new editor is now available under the “Editors” menu tab: The Non Sequential Component Editor (NSC). By default it contains a “Null Object” when the NSC surface is entered into the LDE. Let’s insert a second object, a “Rectangular Volume”. By default, it is 2 x 2 x 1 long, and located at the entrance port:

14. Non-Sequential Zemax Models Let’s reference the Rectangular Volume (NSC 2) to the Null Object (NSC 1) and give the Null Object a Z-position of 5 mm: The block now appears 5 mm “down-Z” from the Entrance Pupil: We could have accomplished the same thing by giving the Rectangular Volume a Z Position of 5mm, but there are advantages to using Null reference Objects that will become evident later. One advantage is that a Null Object only defines a point, and it can’t interfere with any other objects. Hence you can use a Null Object to drag and rotate other real objects without worrying about the Null Object causing an error.

15. Non-Sequential Zemax Models Let’s give the Rectangular Volume enough heft to interact with the rays – this means specifying a material as well: This puts the back of the volume uncomfortably close to the Exit Pupil, so let’s go back to the LDE and move the Exit Pupil back another 5 mm:

16. Non-Sequential Zemax Models Rotating the object (actually, the Null Object to which it’s referenced) shows that it now has an effect on the rays: If we keep rotating, we can see the difference between sequential and non-sequential ray tracing: In non- sequential, the ray is allowed to propagate until it hits any surface: Notice that rays that miss the Exit Port are truncated. This could be fixed either by moving the Exit Port, or enlarging it.

17. Non-Sequential Zemax Models The Entrance and Exit Ports can be shaped by adding apertures to the NSC surface and the surface just after it in the LDE: The “Spider” aperture is meant to model the arms which hold the secondary mirror on mirror telescopes. User-defined apertures (UDA’s) are easy to make: See pages 82 – 86 in the Manual.

18. Non-Sequential Zemax Models What happens if the Object interferes with one of the Ports? Let’s move the block closer to the Entrance Port and rotate it: Eventually (not always right away) a geometry error is generated:

19. Non-Sequential Zemax Models How do you trace a geometry error (assuming it’s not obvious like now)? There is a handy tool under the “Tools” menu in the NSC editor that makes a Non-Sequential Source at the point where the error occurred. This adds a “Source Ray Object” to the NSC. To see the ray, you usually have to turn off the sequential rays in the layout window:

20. Non-Sequential Zemax Models What happens to the NSC source ray if you fix the Geometry Error? Rays from NSC sources (that is, sources described in the NSC editor, and therefore between the Entrance and Exit Ports) stop when they run out of other NSC objects to hit. They won’t exit the NSC group through the Exit Pupil. We can add a detector object to the NSC group after the block to record the NSC rays:

21. Non-Sequential Zemax Models Non-Sequential Detector Objects act like real detectors; They have pixels (you define how many in the NSC editor) which record energy. Some types can record interference fringes and generate Huygens PSFs. Unlike real detectors, some detector types can be arbitrarily curved. Detector input and output is controlled via the “NSC Ray Trace Control” dialog accessed from the main Zemax window via the “Analysis-NSC Ray Tracing-Ray Trace” menu choice. Although in some ways it is easier to use pure NonSequential tracing (you don’t have to get the rays to hit the Exit Port), and it is necessary for systems that don’t have a natural Entrance Port, such as an automobile headlight (the light source is inside the reflector), you lose a number of analysis features (such as MTF and Wavefront measures) and a lot of Merit Function Operands by using pure NSC. For systems that need very specifically described inputs, and diverse analyses, the NSC with Entrance and Exit Ports is best. For systems with unusual geometry, or which have no natural Entrance Port location, the NSC without ports is best. Before using NSC, read at least the NSC Overview in Chapter 12 of the Manual.

22. Non-Sequential Zemax Models Points to remember: 1.Starting Mixed Sequential and Non-Sequential: Add a Non Sequential Compontents “Surface” to the LDE; o The Entrance Port is the position and size of the NSC surface. o The Exit Port is the size of the next surface after the NSC surface. o The Exit Port location is set in the parameters on the NSC surface. o Rays must leave the Exit Port before any analysis can be done. 2.Starting Pure Non-Sequential Modeling: Select “File-NonSequential Mode” from the main Zemax menu o You will no longer have a Lens Data Editor – all objects, including sources and detectors must be placed in the Non-Sequential Components (NSC) editor. o The order of objects in the NSC is unimportant – rays from sources are propagated until they hit objects, or miss all objects. o Analysis of Detector Objects’ output is done via the “Analysis – NSC Ray Tracing” selection on the Main Zemax window.

23. Example Non-Sequential Model Optical Networking Tunable Drop Filter: The filter passes a narrow channel, selected by angle tuning, and the other channels are reflected into a fixed path. Both transmitted and reflected light beams are stationary and can be coupled into single-mode fibers.

24. Example Non-Sequential Model Beam Switch: We use the ability of a rotating block of glass to translate a parallel beam without changing it’s direction: To create a beam direction switch that only uses low precision movement. Blocks unrotated: Beam passes straight through. Blocks rotated: Beam is lowered to mirror, then raised by second block in new direction.

25. Matrix Switch Element Example Non-Sequential Model

26. Matrix Switch Element

27. 3 x 3 Matrix Switch Basic switch elements can be combined to make a “Matrix Switch”: Every input can be switched to every output. Switch movements are non-precision – blocks only need to be aligned to a few degrees, since the beam parallelism is maintained by the accuracy of the block’s fabrication, not its positioning. Example Non-Sequential Model

28. 3 x 3 Switch (1)

29. 3 x 3 Switch (2)

30. 3 x 3 Switch (3)

31. 3 x 3 Switch (4)

32. 3 x 3 Switch (5)

33. 3 x 3 Switch (6)

34. Example Non-Sequential Model The angle sensitivity of an angle-tuned telecom filter becomes very sensitive at high angles. This is an example of a 100GHz bp filter’s tuning between adjacent channels at the low end of the band: 25.000 0 24.977 0 Encoders accurate to 1/300 degree are expensive. We would like a zero-backlash, low angular resolution method of tuning the filter through these small angles. The distance between channels is 0.023 degrees, but the resolution must be 1/10 th that, or 0.003 degrees to avoid interference.

35. Non-Sequential Zemax Models Solution: The “Wobble Filter” Depending on parameters, a 300:1 mechanical advantage is possible at the high- angle (sensitive) end of the tuning range, allowing tuning with only 1 0 precision.

36. Non-Sequential Zemax Models Solution: The “Wobble Filter” Depending on parameters, a 300:1 mechanical advantage is possible at the high- angle (sensitive) end of the tuning range, allowing tuning with only 1 0 precision.

37. Non-Sequential Zemax Models Solution: The “Wobble Filter” Depending on parameters, a 300:1 mechanical advantage is possible at the high- angle (sensitive) end of the tuning range, allowing tuning with only 1 0 precision.

38. Non-Sequential Zemax Models Solution: The “Wobble Filter” Depending on parameters, a 300:1 mechanical advantage is possible at the high- angle (sensitive) end of the tuning range, allowing tuning with only 1 0 precision.

39. Non-Sequential Zemax Models Solution: The “Wobble Filter” Depending on parameters, a 300:1 mechanical advantage is possible at the high- angle (sensitive) end of the tuning range, allowing tuning with only 1 0 precision.

40. Non-Sequential Zemax Models Solution: The “Wobble Filter” Depending on parameters, a 300:1 mechanical advantage is possible at the high- angle (sensitive) end of the tuning range, allowing tuning with only 1 0 precision.

41. Non-Sequential Zemax Models Solution: The “Wobble Filter” Depending on parameters, a 300:1 mechanical advantage is possible at the high- angle (sensitive) end of the tuning range, allowing tuning with only 1 0 precision.

42. Non-Sequential Zemax Models Solution: The “Wobble Filter” Depending on parameters, a 300:1 mechanical advantage is possible at the high- angle (sensitive) end of the tuning range, allowing tuning with only 1 0 precision.

43. Non-Sequential Zemax Models Solution: The “Wobble Filter” Depending on parameters, a 300:1 mechanical advantage is possible at the high- angle (sensitive) end of the tuning range, allowing tuning with only 1 0 precision.

44. Non-Sequential Zemax Models The “Wobble Filter” The LDE consists of only two lenses and a NSC Group:

45. Non-Sequential Zemax Models The “Wobble Filter” The NSC editor references all the rotating parts to the filter support plate: Which is then rotated in the MCE to animate the filter:

46. Example Non-Sequential Model “Beam Walk-Off” in the filter layers is modeled, and the correction by refraction in the filter substrate is shown: Beam walk-off occurs because the light reflects back and forth multiple times in the thin film layers. The idea of a “Contra-Rotating” plate to correct beam walk-off is patented; the author apparently didn’t realize that simply making the substrate thick enough automatically corrects the walkoff. Lack of ray tracing knowledge resulted in wasted time and money.