Applications of self-processing holographic polymers:: fabrication of Diffractive Optical Elements

Computer generation of Diffractive Optical Elements (DOE's) is a method of considerable value since it allows an user encoding of complex optical functions (e.g. lens arrays). As a rule, Computer Generated Holograms (CGH's) are thin amplitude transmission elements. The duplication of such holograms on a photopolymerizable film leads to thick phase holograms with higher diffraction efficiencies. Indeed, the incident optical information is recorded as a modulation of the refractive index. A great advantage of polymerizable materials over other recording systems is that no chemical or heating post-treatment is required once the hologram was recorded. Swelling and shrinkage effects, that are a feature of wet development processes are, thus, avoided. The different methods of duplication taken into account are conventional holographic recording, contact copying and direct imaging of CGH's on polymer layers. Advantages and drawbacks of the three methods will be discussed. The characteristics of the photopolymer developed in the Mulhouse laboratory, such as low degree of optical aberrations and high diffraction efficiency, make it possible to achieve attractive and promising results.