Multicomponent photopolymer systems for volume phase holograms and grating devices

Novel photopolymer systems for the fabrication of high-resolution volume phase holograms and grating devices are reported. Previously reported techniques use a single monomer (or a mixture of similar monomers) and rely solely on density modulation. In contrast, we have found it advantageous to use a mixture of components chosen to have differing reactivities and polarizabilities, which results in a composition modulation. During the image-forming exposure the more reactive monomer is polymerized while the less reactive species is excluded from the irradiated regions. Two-way diffusion, which must be invoked to explain our results, leads to a modulation of the chemical composition and hence of the polarizability of the final material. In some systems the polarizability effect was strong enough to exceed the density effect, even when these factors were in opposite directions. As in previous systems, an over-all exposure is used to fix the images. With appropriate monomer systems, stable images were obtained even when one component was unreactive. The peak-to-peak refractive index differentials achieved in our systems were as high as 1.5%. This is an order of magnitude larger than that reported for initially all liquid systems and 50% larger than that reported for related solid materials. The use of a liquid system enables us to fill small cavities with our materials and then record a high-resolution image. We have made gratings of >3000 lines mm(-1) inside hollow fibers, with 80 microm i.d., filled with a photopolymer material. For white light guided in the core, the expected band-stop filter response was observed.