## 1 Introduction  
Photopolymers are light sensitive materials with adequate characteristics for application as recording material in new devices such as optical elements, holographic memories or as holographic recording media in research. A specific set of parameters is required of the photopolymers: good energetic sensitivity in order to save energy during the recording process, an adequate spectral sensitivity, and a high resolution to enable fidelity reproduction of the stored information. Additionally, new trends in photopolymers include better environmental compatibility, low toxicity, ease of production and good recycling properties. We describe our line of research on this subject and the main results obtained with biophotopol, a new type of photopolymeric material that the Holography and Optical Processing research team at the University of Alicante is developing [1; 2; 3]. Usually, photopolymers have a photoinitiator system that absorbs light and generates free radicals that initiate the radical polymerization reaction of one or various monomers. In the case of holographic recording, the basic mechanism of hologram formation involves modulation of the refractive index between polymerized and non-polymerized zones, corresponding to the \"bright\" and \"dark\" zones respectively, in the diffraction grating generated due to the interference of the recording beams [4]. There are many types of photopolymers, which can be differentiated by the type of binder, since this component determines to a great extent the choice of monomer, dye and initiator used in the photopolymer. Examples of photopolymers with a hydrophobic binder are polyesters of methacrylic acid, which contain acrylic ester type monomers. Photopolymers with a hydrophilic binder include hybrid materials made using the sol-gel procedure. Photopolymers with a poly (vinyl alcohol) (PVA) or gelatine binder and acrylamide (AA) based monomers are also hydrophilic. All these photopolymers have an undesirable feature, the high 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. The environmental compatibility and life cycle are important features that must always be considered when developing new materials [5]. Hydrophilic photopolymers with AA as the polymerizable monomer are versatile materials for use as holographic recording media. Our research team optimized these photopolymers in layers up to 1 mm thick and they were used to obtain holograms with high diffraction efficiency and good energetic sensitivity. These photopolymers have good properties, in particular, their good energetic sensitivity compared with that of other available materials; the possibility of easily adapting their spectral sensitivity to the type of recording laser used by simply changing the sensitizer dye; high diffraction efficiency, together with an acceptable resolution and signal/noise ratio [6]. The high thickness of the 1 mm PVA/AA photopolymer facilitates its possible use in WORM (write once read many) type holographic memories. Using a specific holographic set-up, we multiplexed data pages on this material and determined the response of the photopolymer in terms of different holographic parameters: diffraction efficiency, sensitivity, bit error rate and angular response [7]. 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 confirm its toxic potential [8; 9]. In order to develop a new photopolymer with environmental compatibility we used the 1 mm PVA/AA photopolymer as a reference and evaluated its most environmentally unfriendly components in order to propose alternatives. We developed a new photopolymer called biophotopol with photochemical and holographic features similar to those of AA-based materials but with an improved design from the environmental point of view.