ZEMAX Help for coupling Diode Stack

[Evilmanta]

Hello!

So I've been working on a project to couple a 15 bar diode stack into a 600 micron fiber. Using an old design that I've used in the past but it's giving me some issues. I don't have a plethora of experience with ZEMAX so I'm hoping to leverage the collective consciousness of the internet for some assistance.

I tried using a hybrid simulation first to minimize the spot size and then translate it to a pure nonsequential setup but that didnt' work quite so well. And I'm having little to no luck using the MFE to optimize the Non Sequential layout.

The basic setup is a diode stack, a bi-convex cylinder lens, a plano-convex cylindrical lens, a plano-concave cylindrical lens, and an aspheric lens. All I've been able to do is get the spot size to approximately 0.7 mm but I'm told that it's possible to get it smaller as it's been done before.

The Diode Stack I have configured as follows:
# of Layout Rays: 100
# Analysis Rays: 1000000
Power (Watts): 1500
Wavenumber: 0
Color #: 0
Astigamatism: 0
X-Divergence: 1.146
X-SuperGauss: 1.000
Y-Divergence: 0.229
Y-SuperGauss: 1.000
Number X': 5
Number Y': 15
Delta X: 0.5
Delta Y: 2.0
X-Width: 0.400
X-Width Hx: 5.000
Y-Width: 1.000
Y-Sigma: 1.000
Y-Width Hy: 1.000

This is for a pretty standard diode stack that you can get from most suppliers, in this case Jenoptik. They do both Fast and Slow Axis Collimation on the stacks so I tried to shortcut that by approximating the size of the beam post-collimation lenses. It ends up being a rectangle (per emitter) of 0.5 mm by 1 mm by the time its' exiting the lens. That was the assumed expansion anyways. There are more than 5 emitters per bar but just using a simplification. This may be where a majority of the problem lies.

Following this diode stack is the bi-convex cylinder lens. The two radii are 109.4 mm and the dimensions are 40 by 20mm made of N-BK7.

Object Type: Toroidal
Z Position: 70.6 mm
Material: N-BK7
Radial Height: 20.000
X Half-Width: 10.000
Thickness: 5.000
rotation R1: 0.000
Radius1: 109.400
Radius 2: -109.400

Followed by a Optosigma lens: 022-0662. I rotated it by 180 degrees about the Y -axis and 90 Degrees about the Z-Axis. It's Z-Position is 43.6mm from the Bi-Convex Lens.

After that, another Optosigma Lens: 022-1255. located 22.4 mm from the previous lens

The main point of this entire simulation was to find approximately where to place 1 of 2 aspheres. 1 is a custom lens:
Object Type: Even Asphere
Tilt About Y: 180
Material: SF10
Radial Aperture: 12.368
Thickness: 5.000
Radius 1: 12.368
Conic 1: -1.107
a2 = -0.021477756
a4 = 1.0005501e-005
a6 = -5.7028691e-009
a8 = 7.0445577e-011
a10 = 5.3181675e-013
a12 = -3.3489312e-014
a14 = 3.39617225e-016
a16 = 1.5218404e-018
Radius 2: 0
Conic 2: 0

The best I've been able to accomplish in the fast axis is 0.7 mm spot size. I need to do better. Slow Axis I'm less concerned about for the time being. Anyone have any ideas what I might be doing wrong? Or a way to use the optimizations tools in NSCE?

I can provide some more details or some pdfs of Zemax things I've done. Just let me know

 

[Mech_Engineer]

It would help if you could post some pictures of the geometry and a couple of simple raytraces, just giving the numbers means we have to build your model to see it. Don't forget- a picture is worth 1000 words.

 

[Evilmanta]

Hey! Thanks for the reply. Yeah I was going to put pictures up but I kind of thought I'd see what people wanted to see before I just blindly posted like 20 pictures :)

 

[Mech_Engineer]

Have you done an aberration analysis? Which terms are contributing most to your spot size?

 

[Evilmanta]

I have not done the abberation analysis. This is where my lack of experience comes into play.
As far as I can tell, the distance of the concave lens from and to the asphere & and the radii of the bi-convex/concave lens affect the fast-axis compression.

 

[Mech_Engineer]

You'll have to do a proper aberration analysis to understand what's driving the spot size. When you run an optimization in ZeMax it's important to have a feel for the driving factors in the design and what you're optimization's fitness function should be balancing.

Are you an optical engineer?

 

[Evilmanta]

Electrical Engineer. I have basic training in ZEMAX and was sent to the introductory course for ZEMAX but I haven't had any design training. Mostly just normal optics/photonics courses. So while I understand things like aberration I dont' understand how it affects design and thigns as such. But at the moment I'm the best choice that my company has to do this verification/tweaking. It's just a little more complicated than we thought.

I'll google aberration analysis and some things and get back to you tonight! Thanks for the help so far!

 

[Mech_Engineer]

Honsetly a couple of classes in ZeMax won't cut it... it sounds to me like you might be in over your head, but at least you can do some basic iteration to try and maximize performance given what you already have.

A great quote from one of my optics professors:

The difference between an Optical Engineer and a Mechanical Engineer with optical software is the fundamental understanding of the optical system's limitations and tradeoffs, and how to set up the fitness function in an optimization to take advantage of those properties.

 

[Evilmanta]

Well I appreciate your honesty. It was really supposed to be just a quick simulation/verification that all the lenses were going to work as intended and maybe tweak the distances, and the source was originally set up wrong and like it's based off an existing design so my superiors are convinced that I just need to change some parameters or something isn't set up wrong.

But I totally agree with you, unfortunately I didn't realize Optical Engineering was a degree until later on in my academic career, and I was already well vested in my Electrical degree at U of Michigan, so I maximized the optics courses I could take and went from there since there is no optical engineering major.

Hopefully I can make some progress today and pick your brain some more. Thank youf or all the help so far.

 

[Mech_Engineer]

Look into doing a ray fan analysis and spot diagram of the system. If you can post those, we might be able to give you a little more specific feedback on your system's performance.

 

[Evilmanta]

So I don't know how to get a ray fan analysis/spot diagram in Non-Sequential Mode. I'm like 90% sure I'm just not setting up the source right, but I don't know how else to do it.