optical software
Illuminating optics
Optics for Hire (OFH) using Zemax EE. The
Paul Schreier reviews a sample of the applications and
complete lens is a hybrid of a reflector and
breakthrough products that advanced optics software
small lens, which is placed at the centre to
collect low-angle rays while high-angle rays
have made possible
are reflected by the side of the complete lens
without the need for a reflective coating.
It doesn’t surprise us that state-of-the-art ‘Without this kind of software,’ explains
optics software has made contributions to OFH president John Ellis, ‘engineers would
the development of impressive projects need to calculate by hand each path of the
such as futuristic space telescopes or in the 10,000 to 1 million rays of light – which
cockpit illumination of next-generation would take months compared to minutes or
airliners, but we often overlook how such hours with the software.’
software lets us enjoy the benefits of everyday
products whether automobile headlamps Balancing styling with functionality
or LED flashlights. By examining those We might take automobile headlamps
applications, you can gain an appreciation for granted, but their design can be very
of the multitude of areas where this class of complex. They must provide adequate
software can be applied. illumination of the travel lane and the side
of the road along with enough light to read
collecting scattered light signs, all without blinding oncoming drivers.
Zemax ee analysis of a tir lens in an leD
If you peer into the lighting end of a
flashlight (courtesy of optics for Hire).
Meeting these conflicting requirements is
traditional flashlight with a filament bulb, a delicate balance, states Mike Zollers of
you’ll probably look through a flat piece of diameter (e.g. three inches) and angular Optical Research Associates (ORA). If
protective plastic and see the reflector that diversion (e.g. < 5°). Next you create a given enough volume for the headlamp,
gathers and concentrates the light into a merit function, based on these specifications the design task is relatively trivial, he adds.
beam. In contrast, look into an LED flashlight and enter a starting design that can at least However, a headlamp is a crucial aspect
and you may instead see a very complex trace rays through the system. Activating of a car’s styling, so generally the design
lens. Such a lens is needed because an LED the software’s optimisation routines then team creates a small cavity into which the
is far from a perfect optical source; many varies the parameters of the starting design headlamp must fit. But if the lens area is too
radiate over as much as 180° and also have to provide an initial result, and users can small, it can’t collect enough light.
a ‘batwing’ profile: most light leaves at an also perturb the parameters to simulate The goal is to please the styling department
angle between 40 and 50° with less coming manufacturing tolerances. One interesting yet meet legal requirements that regulate
out straight ahead and little coming at 90°. aspect is that, as Nicholson states, ‘ray things such as vibration, thermal aspects,
This pattern might be good for front-panel tracing is embarrassingly parallel’ because electrical as well as optical standards. Other
controls where the operator wants to see the the rays don’t interact with each other, and questions that arise include: are high/low
LED from many angles but with a flashlight you can divide the several million rays in beams implemented with the same bulb?
or a projector you want a collimated beam the analysis among the number of cores in What is the light source: one of the many
that projects the illumination straight ahead a machine. As do recent versions of other types of halogen bulbs, HID (xenon) lamps,
without any halo effects – and the lens that optics packages, Zemax-EE checks with the or LEDs? Is there just one cavity for low/
creates this column of light from the output operating system to see how many cores are high beams, and do both beams use the same
of an LED is a complex, highly engineered available for the work and transparently optics? Even more important, the headlamp
piece of optics whose aspheric structure divides the computational work among must be manufacturable at a reasonable
varies considerably over the aperture. them – and the speed increase is roughly price. Clearly, headlamp design is a very
Using the Zemax-EE software from Zemax proportional to the number of cores, interdisciplinary task.
Development Corp, it is possible to arrive at assuming the PC has enough memory to ORA’s illumination-design software
an optimised lens that increases brightness keep all the cores busy. for this job, LightTools, works with ray
within the beam by a factor of 10x in only a The figure above shows the cross section tracing techniques. The geometry exists as
few minutes, reports Mark Nicholson, VP of of a TIR (total internal reflection) lens that thousands of B-spline surfaces. For optical
operations. You start with the requirements sits on top of and literally envelopes an LED. analysis, you must determine where light hits
for the flashlight, including the beam This analysis was performed by the company each surface as well as the surface normal at
20
scieNtific coMpUtiNG worlD february/march 2009 www.scientific-computing.com
SCWfeb09 pp20-24 Optical.indd 20 4/2/09 10:47:26
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