Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Low cost HDPE objective

Two optical designs were investigated upon the functional input parameters. The first one is a very low cost solution based on injection moulded optical parts, and particularly Fresnel lenses made of high-density polyethylene (HDPE). HDPE has found extensive use as an optical material for low-end non-imaging applications; extension to high-end imaging applications has so far been prevented by its poor transmittance compared to semiconductor crystals or chalcogenide glasses; this fact makes it necessary to implement HDPE lenses as thin Fresnel elements (<1mm), so as to maximise the radiation throughput. HDPE Fresnel lenses can be manufactured by hot pressing, particularly suited to flat lenses, or injection moulding, required for curved lenses; the former allows a good moulding accuracy, while the accuracy of the latter is limited by the shrinkage of the material (>2-3%), which leads to rounding of the microrelieves and deformation of the substrate.

Lower-risk solutions based on hot-pressed chalcogenide glasses was also considered; In particular the low cost solution is based on a doublet of chalcogenide material. As is known, chalcogenide lenses are less expensive than lenses based on crystalline semiconductors, thanks to the lower cost of the raw materials as well as the cost-effective manufacturability (through moulding).

The HDPE objective was, finally, successfully designed, tested and manufactured.

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