Modern Optical Engineering: The Design Of Optic...
Long-established as the definitive reference on optical engineering and lens technology, Modern Optical Engineering has been updated to include all of the latest advances in optical design technology. The Fourth Edition now contains leading-edge content on optical engineering theory, design, and practice, including new chapters on ray tracing, optical system design, and third-order aberration theory.
Modern Optical Engineering: The Design of Optic...
Written by world-renowned lens designer Warren J. Smith, this comprehensive guide provides unsurpassed coverage of such topics as image formation, basic optical devices, image evaluation, and fabrication and testing methods. With over 150 detailed illustrations, Modern Optical Engineering also features new lens designs as well as new problems and exercises. Copublished with McGraw-Hill.
"Warren was a mentor who always listened, and was always very supportive," said Max Riedl, who worked with Smith at Infrared Industries in Santa Barbara, CA. "A clear and critical thinker, he was never satisfied with 'just' solving an optical problem. During the 23 years we worked together, I never saw any of his designs that did not bring the predicted results."
Long-established as the definitive optics text and reference, Modern Optical Engineering has been completely revised and updated to equip you with all the latest optical and lens advances. The Fourth Edition now contains cutting-edge information on optical engineering theory, design, and practice, including new chapters on ray tracing, optical system design, and third-order aberration theory.
These are the subjects of this "gentle introduction." Our hope is to give you a flavor of what is involved, and to point you to other sources in case you want to learn more. Our business is based largely on what is commonly called "lens design" or (more correctly) optical design. This article is for the general reader who may be curious about this area of applied optics.
One interesting fact about light is that it acts sometimes like a wave, other times more like a stream of very fast particles or quanta called photons. This wave/particle duality remains one of the mysteries of nature, but in practice we emphasize and use whichever aspect makes our calculations easier! In lasers and detectors, quantum effects are especially important, but in optical design, wave or "physical" optics tends to dominate.
Under the right circumstances, we can further simplify our calculations with the additional concept of light rays. Rather than thinking about waves propagating through space, we think about lines that are normal to the waves (i.e., traveling in the direction of the advancing wave front), and we call these lines light rays or simply rays. The behavior of these rays can be modeled by some relatively simple equations (remember Snell's Law?), and much of optical design is therefore based on rays. This is called geometrical optics (don't worry, we still keep track of quantum and physical optics effects when needed to get the right answers!).
As with other fields of engineering, computers are important to many (perhaps most) optical engineers. Computers are used with instruments, for simulation, in design, and for many other applications. Engineers often use general computer tools such as spreadsheets and programming languages, and they also make frequent use of specialized software designed specifically for their field.
With this terminology, the lens designer today is more often called an optical designer, though the older term is still widely used, along with such whimsical descriptive names as "ray bender." It is increasingly common today for "lens designer" to be but one of a number of titles worn by an optical engineering generalist (who may or may not have a specific optics background -- many people doing lens design today are physicists or other types of engineers by original training).
With this background, a lens (or optical system) can actually contain any number and combination of lens elements, mirrors, prisms, rotating polygon scanners, filters, diffraction gratings, holographic elements, and other sorts of optical components. The designer also has to think about what sort of light source will be used with the lens (light bulbs, LEDs, lasers, stars, the sun, etc.). Also important is the type of "detector" (detectors are devices that react to light, such as film, photodetectors, CCD arrays, or the unsurpassed human eyeball). Systems for infrared (IR) and ultraviolet (UV) light expand the number and types of sources and detectors we consider, but the principles are the same, and lens designers work frequently with IR and UV systems as well as with visible light (special materials are often required for IR/UV work since normal optical glass doesn't work well outside the visible spectrum).
So the modern lens designer may work on "lenses" that are a long way from your bifocals or pocket 35 mm camera (although the compact lens in a pocket camera can represent some clever design and cost-effective engineering). If a system uses light in some way (including any system that uses laser beams), lens design is almost certainly involved. Some examples:
The Hubble Space Telescope is perhaps the most famous space-based optical system, and several engineers at Optical Research Associates (ORA was acquired by Synopsys) actually worked on the design and other aspects of the repair optics (ORA even won a NASA award for this and other space-related work).
Optimization - Once you define a set of variables (parameters such as curvature, thickness, index of refraction, etc. that the program can change to try to improve performance), an error function (measure of optical quality, zero typically implying "perfection"), and constraints (boundary values that restrict possible configurations), you are ready to optimize the lens. Numerical methods are used to alter the variables in systematic ways that attempt to minimize the error function while honoring all constraints. Sometimes it goes smoothly, more often it doesn't, so changes are necessary, injecting designer guidance to resolve conflicts (though some software is pretty smart about many types of optimization problems, no program is yet fully automatic, if only because some requirements and esthetic judgments may remain in the designer's head and not in the error function).
Spherical aberration (SA) is perhaps the simplest to understand, since it depends only on distance from the optical axis. Most optical surfaces are sections of spheres, since these are the easiest surface shapes to make . For a simple spherical-surface lens or mirror, rays at different heights on the surface are not bent to the same degree, so they focus at slightly different distances along the axis; this is SA. With simple lenses, you can reduce SA by choosing the right lens form ("lens bending", as we say in the trade). With mirrors (as in the HST), you can correct it by making the mirror a slightly non-spherical conic section (but you have to create the CORRECT conic shape, which was HST's problem -- they built it perfectly against the wrong test standard!). Of course there are OTHER aberrations too, and their interactions may prevent you from making a correction you would like (the old lump-in-the-rug effect -- correct in one place and it pops up in another). This can make lens design a bit challenging (and leads to the next subject of optimization).
Optimization is such an important subject in optical design that we need to say more about it, even though it was briefly described under How to Design a Lens. Remember that the goal of optimization is to take a starting lens of some sort and change it to improve its performance (the starting lens should have a suitable number of optical surfaces of suitable types, since optimization can change only the values of the parameters, not the number or types of surfaces). Since optics is very precise (distances of micrometers can make a big difference), we need to closely determine the values of all our variables at each step of the optimization.
Software can help with almost all of these problems, although the designer remains essential in identifying problems and priorities. Even with all of this, it is still a challenge to turn it all to practice and produce lenses that meet all the requirements in actual use. If you are interested in optical design tools, the Optical Solutions Group at Synopsys offers several software solutions to help you achieve your objectives. For help choosing which optical design software is best for your application, visit our Choosing An Optical Design Software Solution page.
The Optical Engineering track addresses the growing demand for skilled professionals who can conceptualize, design, and manufacture optical components and systems. This track emphasizes lens design, radiometry (sources, optics, and detectors), and optical systems engineering.
Conceptual block diagram of the designed ultrawide-angle optical system for ophthalmology and dermatology applications: (a) focused in the eye, (b) unfocused to cover a wide area, and (c) focused outside the eye.
Primary Text: Optics, 4th edition, by Eugene Hecht, (Addison Wesley Longman, 2002) Supplementary Text: Modern Optical Engineering, 3th ed., Warren J. Smith, Mc Graw Hill, 2000) Course Details: Optical devices are employed in an ever increasing range of applications, from simple lenses to electronic cameras and displays, to complex fiber-optic communication networks. This course provides an introduction to modern optical engineering, covering the fundamental concepts as well as practical techniques and applications. Basic optical principles are presented, particularly reflection, refraction, aberrations, diffraction, interference, brightness and coherence. Practical aspects of optical materials will be covered as well. Building on this foundation, a wide variety of optical devices and processes are then discussed, including lenses and imaging systems, prisms, simple optical instruments, fiber optics, photodetectors, and lasers. 041b061a72