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- How to Perform Freeform Optical Design
How to Perform Freeform Optical Design
- By Mark Nicholson
- Published 1 May 2009
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DLS Optimization
We will now optimize this design using the Damped Least Squares (DLS) optimizer:
Note that each evaluation of the merit function traces 100,000 rays. On the author's dual-quad-core machine, this optimization completes in 20 minutes and yields this design (available as freeform_after_dls at the end of this article):
This design yields a total power of .89 lm, and a peak brightness of 4.2 lm/sr, which is almost 10 times brighter than the starting point. The RMS angular radius is now about 16° (was 49°). At its narrowest point the pipe has a radial height of 1.6 mm. Of the five inital equi-spaced datapoints, three are now in the first bump, and so the data points have moved down to 'shape' the light as it is emitted from the LED.
If we now use the Hammer optimizer on this design, we will get this result (freeform_after_dls_hammer):
Remember that the Hammer optimizer does not self-terminate, and it will carry on forever until the user stops it. In this case the Hammer was run unattended for a few hours. Note that the Freeform object has optimized into a shape very similar to a Compound Parabolic Concentrator (CPC) object. ZEMAX supports a rotationally symmetric CPC object and a Rectangular CPC object. It is left as an exercise for the reader to see if native CPC objects yield better or worse performance than the freeform object in this case.
This is a nice example that sometimes the 'non-parametric' Freeform will tend to an underlying parametric shape if that is a good fit to the problem in hand. Generally speaking, parametric objects will optimize faster than the Freeform object because they require fewer defining parameters.
The hammered design yields a total power of .87 lm, and a peak intensity of 27 lm/sr (>50 times brighter than the starting design!), and has an angular RMS radius of 6°.
Note that each evaluation of the merit function traces 100,000 rays. On the author's dual-quad-core machine, this optimization completes in 20 minutes and yields this design (available as freeform_after_dls at the end of this article):
This design yields a total power of .89 lm, and a peak brightness of 4.2 lm/sr, which is almost 10 times brighter than the starting point. The RMS angular radius is now about 16° (was 49°). At its narrowest point the pipe has a radial height of 1.6 mm. Of the five inital equi-spaced datapoints, three are now in the first bump, and so the data points have moved down to 'shape' the light as it is emitted from the LED.
If we now use the Hammer optimizer on this design, we will get this result (freeform_after_dls_hammer):
Remember that the Hammer optimizer does not self-terminate, and it will carry on forever until the user stops it. In this case the Hammer was run unattended for a few hours. Note that the Freeform object has optimized into a shape very similar to a Compound Parabolic Concentrator (CPC) object. ZEMAX supports a rotationally symmetric CPC object and a Rectangular CPC object. It is left as an exercise for the reader to see if native CPC objects yield better or worse performance than the freeform object in this case.
This is a nice example that sometimes the 'non-parametric' Freeform will tend to an underlying parametric shape if that is a good fit to the problem in hand. Generally speaking, parametric objects will optimize faster than the Freeform object because they require fewer defining parameters.
The hammered design yields a total power of .87 lm, and a peak intensity of 27 lm/sr (>50 times brighter than the starting design!), and has an angular RMS radius of 6°.