Molding Hybrid Diffractive IR & Plastic Lenses: More Power, Less Glass

Posted by Aimee Schenck on Dec 7, 2016 10:30:00 AM

A hybrid diffractive lens is a refractive optical element with a custom-designed diffraction profile encoded onto one surface. Such a hybrid literally combines the power of refraction and diffraction; as such, a single hybrid lens can replace two or more refractive lenses, especially when utilizing aspheric surfaces. Furthermore, because diffractive surfaces have “negative optical dispersion,” a hybrid lens can make an excellent single-element achromat(*). This technique of combining multiple lenses into single hybrid lenses enables optical designers to reduce the overall mass, volume, and material cost of an optical system.

Hybrid diffractive lenses have particular appeal to IR system designers who are challenged by both fewer materials and higher costs. To date, there have been few options for high-volume fabrication of diffractive aspheres. Conventional manufacturing methods are limited to engraving the diffraction pattern onto the refractive surfaces one at a time, using single-point-diamond-turning (SPDT). While RPO certainly has a host of SPDT machines to produce individual hybrid lenses to support small-volume customers, when it is time to step up production, RPO is able to offer unique fabrication capabilities.

RPO’s core technology is our innovative approach to precision glass molding of optical elements. Once a hybrid optical element has been designed and tested, it is a straightforward process for RPO to convert that design into a mold master of the hybrid part. From that point, producing the hybrid optical elements is only slightly different than producing a simple spherical element. The up-front cost of creating the mold master sees an immediate return on investment. The break-even point is quite low, especially for expensive IR materials.

Our customers are already seeing the tremendous power that diffractive hybrid lenses provide. In one recent thermal imaging project, we enabled a customer to replace twelve surfaces in the initial design with only two hybrid lenses — a three-fold reduction in material cost alone!

If you think your project could benefit from our diffractive hybrid lens capabilities, contact our optical engineering team to see how they can help you.

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(*) The base lens acts as the crown while the diffractive surface functions as the flint, both with positive optical power.

Topics: Infrared, Molded Optics