Holographic photomaterials

Holographic photomaterials belong to the class of photosensible materials that present appropriate performances to be used in holographic techniques.

These performance requirements include: high diffraction efficiency (near 100%), high refractive index modulation Dn, high spectral selectivity, low scattering, high surface optical quality, dimensional and temporal stability and low production cost.

For decades, the concurrence of such characteristics in a single type of photomaterial has been a challenge in the field of holography and holographic data storage. 

The idea of holographic storage was first proposed in 1963 by Pieter J. Van Heerden at Polaroid who predicted that a volume V of holographic recording medium can store about V/(l3) bits of information (where l is the wavelength of light used in the holographic storage device). This yields 6 terabits of information in a cube-of-sugar-like, 1 cm3 storage volume, using green light of wavelength 550 nanometers. This impressive storage capacity can be further increased by several orders of magnitude with sophisticated spectral hole-burning techniques that can overlap as much as 108 different data pages in a single spot of the storage medium (each data page being recorded by a slightly different light frequency).

Our group (GICO-UCM) has been the first one in the world to fabricate in 2001, at the level of a unique prototype, a photopolymerisable glass, under the collaboration with Dr. Cheben at the National Research Council of Canada exhibiting the above mentioned performances. The photopolymerizable glass belongs to the class of hybrid porous inorganic-organic photomaterials. It is synthesized by the sol-gel technique.

As an example of what can be achieved, a 1 mm thick holographic recording material can store up to 100 bits (or pixels) per squared micron, which is 20 times the storage density of a single-layer digital video disk (DVD) (the latter being 4.5 bits per squared microns).

Similar hybrid organic-inorganic glasses can also find applications in re-writable data storage, image processing, programmable optical interconnects and neural networks. This new photosensitive glass has been covered by a number of press releases, including:



Photopolymerizable glass incorporating High refractive Index Spices (HRIS)

 As a continuation of the 2001 proposal, in 2006, and under the collaboration with Dr. Francisco del Monte, from the Institute of Materials Science (CSIC, Madrid), a new generation of photo-polymerizable glass incorporating High Refractive Index Species (HRIS) was developed, based on Zr isopropoxide, gelated with metha-crylic acid and incorporated at a molecular level. This photomaterials exhibits high diffraction efficiency (near 100%), very low scattering due to the nano-composition structure, and very high refractive index modulation. For the first time, to the best of our knowledge, it was achieved a refractive index modulation in a holographic grating recording in such a photomaterial of: Dn = 10-2. The picture displays the phase transmission holographic grating with rich and depleted regions containing the Zr. (From:  F. del Monte et al., Adv. Mat, 18, 2014-2017  (2006))