It would be impossible not to notice the rapid increase in 3D media over the last few years. Of course the most widespread of these is the return of 3D to the cinema screen. In this case the movies deliver a separate image to each eye by using glasses to filter out specific polarization states. By using a separate perspective for each eye it is possible to produce the illusion of depth. This technology is thus limited to providing just two perspectives, which is fixed during filming.
Researchers based at the University of Arizona and Nitto Denko Technical have succeeded in making great strides towards real time holography. This has the advantage over polarization spectroscopy, as special glasses are not required, and the viewer is free to choose the viewing angle. The new development means that the team can record and display moving, color holograms [Blanche et al., Nature, (2010) 468, 80].
This isn’t the first time that an updatable display has been built, as photoreactive organic crystals have also been used to create color holograms. However due to the difficulty of producing these crystals it is unlikely they will ever spread beyond the laboratory. Two years ago Blanche and coworkers premiered their approach to the holographic display in the form of a photo-reactive polymer. At that time the display was monochromatic and it took over four minutes for the image to be re-written. In addition the system was also very sensitive to the environment; having to be shielded from vibrations and temperature changes.
Now the team has managed to produce a display that can be refreshed in two seconds, meaning that motion can be conveyed, albeit in a somewhat stilted fashion. This is an improvement of greater that two order of magnitude in just two years.
Lead author Prof. Pierre-Alexandre Blanche explains that the photorefractive polymer works by changing its refractive index when illuminated by photons (particles of light). He told Materials Today that “when photons strike the polymer, it generates electrical charges. Both negative (electrons) and positive (holes) charges are created. But only one of those can move in the polymer matrix.” The result is a charge difference between light and dark regions, which means there is an electric field between these areas. Molecules whose refractive index is directionally dependent then align according to the electric field.
If this technology is to make it to market the refresh rate will have to be increased to a true video rate, of 30 images per second. This means another 100 fold increase. However, if the groups can achieve the same rate of improvement, we may only need to wait another two years.
Stewart Bland