Photopolymers are useful for different applications such as in the development of holographic memories or holographic
optical elements. Photopolymers have an undesirable feature, the toxicity of their components and their low
environmental compatibility, particularly if we analyse the life cycle of the devices made with these materials and their
interaction with the environment. In this sense the University of Alicante has patented new dry biocompatible
photopolymer: Biophotopol. Initially this new photopolymer was optimized to holographic memories application. The
main goal of the previous works was to achieve thick stable layers. On the other hand polyvinyl/acrylamide (PVA/AA)
photopolymers have been widely studied by many research teams. The main drawback of an AA-based photopolymer as
far as the environment is concerned is the acrylamide, a substance which has been known to be carcinogenic for many
years. Recent investigations have characterized PVA/AA based photopolymers at very low spatial frequencies. In
previous works we have proposed the application of interferometric techniques, both in transmission and in reflection, to
characterize in real-time the modulation performance of the photopolymers. We used this approach to characterize the
optical modulation properties of a PVA/AA photopolymer. With this scheme we mainly characterize the properties at
very low spatial frequencies, which can be useful to analyze the applicability of holographic recording materials in
another range of applications, such as recording of diffractive optical elements (DOEs). In this work we have compared
Biophotopol to PVA/AA photopolymers.
Polyvinyl/acrylamide (PVA/AA) photopolymers are often used as holographic recording materials. Depending on each
particular application, different spatial frequencies can be recorded. The only limitation appears when high spatial
frequencies are stored (over 2500 lines/mm the diffraction efficiencies achieved are very low). This cut-off spatial
frequency is due to the finite size of polymer chains. On the other hand, in the case of very low spatial frequencies,
monomer diffusion times are highly increased and so there are important distortions in the shape of the gratings stored.
In order to characterize the hologram formation in these types of materials, many parameters must be taken into account.
One of the most important parameters to measure is the diffusion of the molecules inside the layer. In this sense, when
very low spatial frequencies are recorded, component diffusion and thickness variations can be determined more
accurately. In previous works, we have characterized the photopolymer at the zero spatial frequency limit, where
diffusion does not take place, measuring the refractive index variations and the shrinkage. In this work we have recorded
different long period gratings (at very low spatial frequencies diffusion starts to be important) and we have analyzed the
profiles formed in the material during exposure and the refractive index distributions. This study has been carried out
measuring the transmission and reflection orders of diffractive gratings. Furthermore, to obtain a deeper insight into the
profile of the gratings recorded and especially into the sharpness of their edges, we have obtained numerically the
diffraction-efficiency values fitting a Fermi-Dirac function to each profile.
Recently, we have proposed the application of interferometric techniques, both in transmission and in reflection, to
characterize in real-time the modulation performance of the photopolymers. In this work we use this approach to
characterize the optical modulation properties of a polyvinyl alcohol/acrylamide (PVA/AA) photopolymer. A double
beam interferometer is constructed, both in transmission and in reflection, in combination with the setup to expose the
recording material. Some benefits are provided by this approach: direct calculation of the properties of the material is
possible, index and surface modulation can be decoupled, and additional information can be obtained since the results are
not influenced by diffusion processes. With this scheme we mainly characterize the properties at very low spatial
frequencies, which can be useful to analyze the applicability of holographic recording materials in another range of
applications, such as recording of diffractive optical elements (DOEs). Comparison with the conventional holographic
characterization shows significant differences.
We present the characterization and the optimization of the phase and amplitude modulation of a liquid crystal display
(LCD) applied to holographic data storage. We discuss the main LCD modulation regimes demanded in the literature in
the application to holographic memories: binary amplitude, binary phase and hybrid ternary modulation (HTM). We
show how to obtain optimally these modulation regimes with a LCD. In our strategy it is essential the accuracy
demonstrated by the model we use to describe the modulation properties of the LCD. This accuracy allows for a reliable
computer search of the configurations enabling for an optimum LCD complex amplitude modulation. Results are given
for the calibration of a commercial LCD. Optimum configurations close to the ideal for each of the modulation regimes
are also obtained and the values of the various parameters characterizing the quality of these configurations are provided.
We have also analyzed the performance of these configurations to perform the Fourier transform (FT) of a binary data
page. We see that the optimum configurations obtained for the binary phase and the HTM regimes produce a
homogeneous distribution of the energy in the Fourier plane with no DC peak.
We present a fruitful student's lab experiment allowing for an effective learning of some of the basics in physical optics. We proceed with the characterization of the surface structure of a compact disk (CD) and a digital versatile disk (DVD). This experiment is an effective means to have a direct hands-on experience on diffraction, Young's fringes interference phenomena, and diffraction chromatic dispersion. The fact that both CD and DVD are widespread consumer electronics devices enhances the interest of the student on the experiment.