Achromatization for Multiple Narrowband Sources using Hybrid Multi-Order Diffractive Lenses

Abstract

Surface relief diffractive lenses that utilize multiple diffracted orders were first introduced by Sweeney and Sommargren1 and Morris and Faklis2. More comprehensive discussions of these lenses were later presented3,4,5. These multi-order diffractive (MOD) lenses were shown to have the same optical power at a discrete set of resonance wavelengths within a chosen spectral region. The physical difference between a standard diffractive lens and a MOD lens is that the OPD at the zone boundaries of a standard diffractive lens is equal to the design wavelength, whereas, for a MOD lens the OPD is equal to an integer (>1) multiple of the design wavelength. As a result, the diffraction efficiency for each order of a MOD lens has a reduced spectral bandwidth. This efficiency reduction indicates that MOD lenses may be best suited for optical systems which utilize discrete wavelength sources as opposed to broadband sources. This paper will investigate the use of MOD lenses in this class of systems by examining the combination of refractive and diffractive lens power to achieve proper achromatic control in a manner analogous to the standard hybrid lens approach. These hybrid lens combinations may be well suited for applications such as color laser printing and laser machining. Several first order design examples are provided including a two-color hybrid achromat with nearly 100% diffraction efficiency and a three-color hybrid apochromat made from a single material.