Design concepts for diffusive holographic photopolymers

Abstract

Diffusive photopolymers are an area of intense recent materials development, spurred by interest in holographic data storage, display holography, and custom diffractive optical elements, among other applications. This review examines a range of photopolymer formulations of academic and commercial interest, and places their design strategies in context via quantitative analysis of the recording fidelity, maximum refractive index change and the degree to which they achieve this limit. Finally, this analysis is extended to estimate the scope of achievable future performance improvements. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1021–1035.

Cyclic allylic sulfide based photopolymer for holographic recording showing high refractive index modulation

“…The Δn achieved F I G U R E 3 Diffraction efficiency curve of sample 1 measured at 632.8 nm (p-polarization) as function of the incidence angle with relative fit with the Kogelnik equation is of 0.0061, which corresponds to 35% of the formula limit. This result is consistent with the studies reported in the literature, 27,37 where it is shown that the usable fraction of Δn limit is between 30% and 60% for photopolymer formulations using CAB as binder. The diffraction efficiency was remeasured after 1 month without any apparent change, proving that the grating is stable in time, as also reported in a previous work.…”

“…In order to predict the performances in terms of refractive index modulation (∆n) of a photopolymer system, the formula limit (Δ n limit ) 27 can be computed. It corresponds to the difference between the refractive index of the mixture ( n ave ) and the refractive index of the background material ( n 1 ): Δ n limit = n ave − n 1 .…”

“…24,25 Considering the standard photopolymers, only a certain fraction of the monomer present in the formulation usually diffuses and polymerizes with the desired spatial distribution, thus contributing to Δn. 26,27 This limitation in the Δn may be mitigated by increasing the concentration of the active monomer, but a solubility limit exists and it depends on the monomer/matrix combination. 28 Moreover, it is not effective to have unreacted species inside the film that have to be consumed during the bleaching step (i.e.…”

Numerical Technique for Study of Noise Grating Dynamics in Holographic Photopolymers

“…However, when diffusion is sufficiently fast that radicals can diffuse into the dark region of the fringe before terminating (R m * 1), the visibility of the radical distribution decreases inversely proportional to period squared. This behavior has previously been identified as the resolution limit in published materials [9]. This explains the observation that significant improvement in dynamic range can be achieved by increasing the termination rate via radical traps on the matrix [10].…”

Improving performance oftwo‐stagephotopolymers for volume holographic recording by fluorinatedepoxy‐amine cross‐linkedmatrices

“…Thereby a holographic grating with refractive index modulation (Δn) is gained finally (Figure 1). [5][6][7][8] Many kinds of cross-linked host matrices have been reported, which are a mixture of at least two active substances, such as epoxy-amine, epoxy-thiol, isocyanate-alcohol, orthoester-anhydride, and thiol-allyl. [9][10][11][12][13][14] Compared with other cross-linked systems, epoxy-amine has excellent mechanical properties and low volume shrinkage, which is very important for millimeter-thick media in holographic data storage.…”