2012

Designing Optical Systems With Off-The-Shelf Products

Utilization of COTS (commercial off-the-shelf) products is now almost a bylaw of government and military design projects and is becoming of increasing interest in commercial designs, as well. Optical systems are no exception; the use of stock optics can provide tremendous advantages in terms of reduced cost and development effort. The key is finding the most appropriate way of employing stock optics in a custom design.

altThe obvious benefit of using COTS products is reduced cost. Volume production yields reduced unit cost, especially in optical components. Using a stock product avoids setup fees and tooling costs that can make a custom optic as much as ten times more expensive in small quantities. Further, that differential only begins declining when production volume reaches 1000 pieces, a quantity seldom reached in high-end optical system manufacturing.

Stock optics can also help reduce design and development time because they are readily available. Rather than waiting months for a custom optic to arrive before assembling a prototype to begin testing, designers can obtain stock optics overnight. This high availability also provides benefits during final production by eliminating the need to maintain an expensive in-house inventory. Because vendors seldom discontinue or alter their stock optics, supply issues seldom arise.

Custom vs. Stock

altThere are drawbacks to using stock optics in certain situations, however. Stock optics work best when the optical system is relatively slow and paraxial in its design requirements. An optical speed of f/8 or higher with a field angle of 15° or less are easy to obtain using only stock components. When seeking lower f/#, though, the ability to customize the exact curvature, composition, and coatings of lenses may prove more efficient than restricting a design to using only stock optical components. Despite the vast range of stock components available, there may not be a precise match to the design’s needs. Any mismatches will compound the need for making design iterations in order to optimize performance. When performance needs are extremely demanding, then, custom optics may provide the fastest route to final design despite the wait for initial delivery.

Custom optics may also be necessary when the optical system must meet tight size and weight constraints. While a design composed of stock optics may be able to achieve the same performance as one using custom components, the stock design may involve multiple lenses and a longer optical path to achieve the equivalent performance of a single custom lens. When size and weight are critical, then, custom optics may be essential.

Often a system that will employ custom optics in the final design, however, will want a stock component solution for the early stages of development where availability and low cost are critical. A development team might, for instance, need to create a demonstration or proof-of-principle prototype in order to obtain funding for full product development. A prototype optical element may also be needed in order to support the development and evaluation of other system elements before establishing definitive final optical performance requirements. Custom optics can quickly become prohibitively expensive when there are many design iterations involved.

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