Because the radius of curvature of an aspheric lens varies with distance from its optical axis, it can require more complex fabrication techniques than a conventional spherical lens. Each of these techniques has its own advantages and disadvantages.
Precision glass molding of aspheric lenses
During precision glass molding, optical glass cores are heated to high temperatures until their surfaces become malleable enough to be pressed into an aspheric mold. They are then cooled to room temperature, maintaining the shape of the mold. Until recently, the technology was not available for lenses greater than 10mm in diameter, but new tools, optical glass and metrology processes have made larger lenses possible. Creating the mold increases initial startup costs, but once the mold is finished, the incremental cost for each lens is lower than that of standard manufacturing techniques, making it a favorable option for high volume production.
Precision polishing of aspheric lenses
Grinding and polishing one aspheric lens at a time has been the standard manufacturing technique, but technological advances now allow for previously unattainable levels of accuracy. Computer controlled precision polishing can automatically adjust tool dwell parameters to polish away high spots where more polishing is needed. If higher quality polishing is required, magneto-rheological finishing (MRF) is used to finalize the surface. This provides high performance surfaces unattainable using standard polishing techniques because of its precise control of the removal location and high removal rate. While other manufacturing techniques require specialized molds, precision polishing utilizes standard tooling, which makes it the primary option for prototyping and low volume production.
Plastic molding of aspheric lenses
Plastic molding involves injecting molten plastic into an aspheric mold. Since plastic is not as thermally stable and resistant to pressure as glass, it requires special treatment to create a comparable aspheric lens. Nevertheless, plastic is advantageous because it is light weight, easily molded and can be integrated with a mount to create a single piece. While the selection of optical quality plastic is limited, its cost and weight benefits sometimes dictate its use.
Selecting the appropriate aspheric lens
Based on your requirements for volume and cost, the experts at Esco Optics can help you select the exact aspheric lens and method of fabricating it that best fits your requirements.