Achromatic refractive–diffractive double-relief microprisms

Abstract

The Fresnel-prism technique has become an important medical option for the diagnostics and treatment of strabismus in children. However, the application of prisms in ophthalmology generally involves chromaticity problems: the formed optical images are distorted due to the dispersion of white light at the microrelief and the applied microprisms reduce the contrast of the images of the test charts, and in turn, the accuracy of eye diagnostics drops. In this study, a novel method was developed for the total chromatism compensation using a special microprismatic refractive–diffractive structure with double microrelief: the first refractive microrelief was used for light beam deflection, whereas the second diffractive one was used for compensating the chromatism of the first microprism. The dispersion chromatism of the first refractive prism and the diffraction chromatism of the second microprism grating are oppositely directed. Thereby, dispersion chromatism can be completely compensated by diffraction grating. The optimal characteristics of these achromatic refractive–diffractive structures were calculated, and the necessary angles and optimal relief pitches of the ophthalmic microprisms were obtained. Achromatic structures were manufactured according to the calculated parameters, and their optical characteristics were experimentally investigated. The main advantage of such optical devices is that they are flat and very thin. The findings indicate the possibility of designing effective achromatic microprisms.