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How to Perform Freeform Optical Design
- By Mark Nicholson
- Published 1 May 2009
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OD Optimization
We now return to the starting design, and repeat the optimization using the Orthogonal Descent (OD) optimizer:
This design is very different to the other two:
It can be seen that by using a narrow neck at the start of the freeform shape, high-angle light is lost, but the remaining energy is well collimated. Only 0.61 lm of power is transmistted, but the peak beam brightness is almost 10 lm/sr, and the RMS angular cone is 8°. The file is available as freeform_after_OD at the end of this article.
Running the Hammer optimizer with the Orthogonal Descent optimizer used as the local optimizer yields a radically different design:
Note that this design does not use total internal relection at all, and is purely refractive. This implies that a two-lens solution exists and is worth investigating! The design yields a total transmission of 0.99 lm, a peak brightness of 78 lm/sr (>150 times the original brightness) and an RMS angular radius of 4°.
This demonstrates another of the key benefits of the freeform object. A CPC object when optimized can only yield the best-form CPC object, obviously. The Freeform object can take whatever shape yields the lowest merit function. This may be useable directly itself, or it may point to other objects to be used. In this case, it is worth investigating what a two-lens design could offer instead of a lightpipe.
This design is very different to the other two:
It can be seen that by using a narrow neck at the start of the freeform shape, high-angle light is lost, but the remaining energy is well collimated. Only 0.61 lm of power is transmistted, but the peak beam brightness is almost 10 lm/sr, and the RMS angular cone is 8°. The file is available as freeform_after_OD at the end of this article.
Running the Hammer optimizer with the Orthogonal Descent optimizer used as the local optimizer yields a radically different design:
Note that this design does not use total internal relection at all, and is purely refractive. This implies that a two-lens solution exists and is worth investigating! The design yields a total transmission of 0.99 lm, a peak brightness of 78 lm/sr (>150 times the original brightness) and an RMS angular radius of 4°.
This demonstrates another of the key benefits of the freeform object. A CPC object when optimized can only yield the best-form CPC object, obviously. The Freeform object can take whatever shape yields the lowest merit function. This may be useable directly itself, or it may point to other objects to be used. In this case, it is worth investigating what a two-lens design could offer instead of a lightpipe.