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Due to the factors of cost and time, it is common to prototype a design before committing to building production molds or masters. Prototype systems can be used for multiple purposes, such as evaluating the optical performance of a design, testing assembly methods and tolerances, and developing fixturing. They can be also be used by marketing or salespeople to show a company's capabilities, give demonstrations at conferences, or gain customer feedback. In this chapter, we discuss different methods of prototyping a design, both creating the optical and optomechanical parts, as well as issues with assembling and testing the prototype.
7.1 Optics
In order to fabricate prototype optical parts, the first effort is to generate a set of drawings or electronic files. It may very well be that the prototype parts will not have all of the features of the final production parts, so a prototype drawing (as opposed to a production drawing) is required. In some instances, multiple prototype configurations may be developed, with relatively small changes between them, or the parts may be produced by multiple methods. This may require multiple drawings or dash numbers on the drawing to call out the different configurations.
The drawing for the prototype optic should be created with the manufacturing method in mind, as the features included on the prototype parts may partially depend upon the method used to produce them. Prototyping of optical elements is usually performed either by machining (almost always diamond turning) or by molding. A diamond-turned part is unlikely to have gate vestige, or a gate flat, unless it is specifically requested. Similarly, a diamond-turned part does not require draft, although it can be produced with it. Neither method is likely to produce a representative cavity ID, but one could be machined or molded in if necessary. Proper placement of a cavity ID during the design process should limit its effect on any system performance, so in this case not having one on a prototype part should not be a significant issue. Consideration of how closely the prototype part needs to represent the production part may influence the choice of the method of its fabrication as well as determine how complicated the prototype manufacturing process must be.
As mentioned previously, most of the commonly used optical plastics can be diamond turned. Some of the materials (such as polycarbonate, PEI, and PES) do not diamond turn as easily as the others and require extra attention. In the case of PEI and PES, postpolishing is sometimes required to obtain a desired surface roughness. For the other optical plastics, postpolishing should not be necessary.
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