HOLOGRAMS are a staple of science fiction. For many, the very word will conjure an image of Princess Leia from “Star Wars” (pictured), or of the holodeck of the starship Enterprise. Making real moving holograms, though, remains tricky. Every approach tried so far represents a trade-off between the quality of the image, its size and the cost of the kit that produces it—and making the first two acceptable means the third is exorbitant. That could change, though, if Daniel Smalley of Brigham Young University, in Utah, and his colleagues have their way. They have made a gizmo which they hope will eventually be able to project screen-sized moving holograms for not much more than the cost of a high-end television set.

Holography works by squashing all of the three-dimensional information in a scene into a structure called an optical grating. When this grating is illuminated, light bounces off its bumps and troughs in such a way that the reflection reconstructs the original scene. An unchanging grating yields a static hologram, such as is found on a bank card. But gadget-makers and military types would dearly like to use similar trickery to create holo-videos, by continuously varying the grating’s geometry.

Most attempts to do so involve modified liquid-crystal displays (LCDs). But, although commercial LCDs are cheap, the bespoke screens required for holography are costly because they need far smaller picture elements. Dr Smalley’s team, therefore, take a different approach, the latest iteration of which they have just reported in the Review of Scientific Instruments.

Their story began when Dr Smalley was plain Mr Smalley, a student at the Massachusetts Institute of Technology. In 2013 he published the design of a chip that costs roughly $10 to produce and which is capable of making a small, simple hologram.

The chip is a crystal of lithium niobate that has a light-carrying channel called a waveguide carved into it. Lithium niobate is piezoelectric—meaning that when a voltage is applied to it, it contracts or expands, becoming more or less dense as it does so. If the voltage varies, this makes moving patterns of more- and less-dense material. Changing the frequency with which the voltage varies changes the pattern. Since light takes different paths in material of different densities, such patterns can form optical gratings that change sufficiently fast to create moving holograms.

As light passes through such a grating it is diffracted into a horizontal fan, forming a holographic line that is equivalent to one line of a television display. This can then, if desired, be run through a scanner that splits it up into multiple lines, one above another, generating a picture. Using this method, Dr Smalley was able, by employing red, green and blue light simultaneously, to create a coloured, holographic image.

Unfortunately, this single-waveguide image can be seen only by looking straight along the waveguide’s axis. The next task, therefore, is to scale the design up by linking many crystals together, to create an image both bigger than a single crystal’s display and capable of being seen from lots of directions. That means controlling precisely where the optical output of a waveguide goes—which is what Dr Smalley’s latest paper is about.

To align the outputs of many devices, the team needed to know in exquisite detail how the colour and angle of light coming out of each one of them change as the voltage frequency is altered. That is no mean feat of measurement, but by using a bespoke system of detectors Dr Smalley and his collaborators have discovered the crucial voltage frequencies that diffract different colours independently of one another but at angles which overlap nicely. This will allow multicoloured images to be created from numerous waveguides in a way that resembles Monet rather than Jackson Pollock.

In principle, such a display should be able to produce room-sized holograms. Turning that principle into practice will take a while. But if the system does scale up in the way Dr Smalley hopes it will, then living-room holography may be yet another hoary prediction of the future that actually does arrive in the present.