Research On Applications Of Multi-Layer Diffractive Optical Elements

This paper provides an overview of development of muliti-layer diffractive optical elements and the basic theory of muliti-layer diffractive optical elements. Characteristics of multi-layer diffractive optical elements (DOEs) are discussed. Optimization design of the maximum grating depth of multi-layer DOEs is presented and diffractive efficiency contribution of the two single-layer DOEs which compose multi-layer DOEs to the efficiency of the whole element is analyzed principally. Through the way of optimization design of the maximum grating depth, an example of a multilayer diffractive optical element which employs material of PS and PMMA is given. The minimum diffractive efficiency of this multi-layer DOE is greater than 98% in 0.436～0.656nm visible waveband. So multi-layer DOEs can improve broadband efficiency while for single-layer DOEs, the broadband efficiency falls down obviously when the wavelength is off the design wavelength. Then, a long focal length objective lens with that elemet is designed. In the system, the focal length is 1000mm, the entrance pupil diameter is 125 mm, the field angle is 3.5°, the spectrum is from 510 nm to 656.3 nm while the design wavelength is 589.3nm, MTF is higher than 0.35 in 1001ps/mm.Multi-layer DOEs used in hybrid diffractive-refractive optical systems not only have benefits to imaging quality but also to reducing weight and complexity of optical systems. Instead of employing special expensive material in some systems, cost of optical systems is reduced. All above indicates that multilayer DOEs are significant to application of optical systems.