If you need to ask why you would need a transparent smartphone, you probably don’t really need one. After all, not only would it be hard to find, particularly if transparent when powered down, but others could easily see exactly what you are working on. It is only when you take a step back that you realise that the state of being non-transparent, or opaque, is the weaker condition.
If by nature you possess transparency, opacity can be just another option under a menu, while the converse is clearly not true. The real power once you have it, is not just that you get opacity for free, it is that you get everything else in between. A prototype device being developed by Polytron Technologies from Taiwan, pictured above, shows some of the challenges to making the transparent smartphone a reality.
Butterflies and jellyfish (pictured above) have the unique ability to extract pigment-free colour directly from the quantum, so to speak, through precisely configured scales or undulating cilia – tiny “hairs” that protrude from a larger cell. They use these bio-antennae to blink out a measured photon whenever the distance between these hairs matches the wavelength of the illumination that strikes them.
Other organisms, particularly the smaller and thinner ones, have more direct means to utilise or deal with incoming radiation as the case may be. Often they must spend significant energy just to shield their DNA from the mutagenic rays which penetrate their cells. They also may need to work hard just to be able to be seen by their peers. When creatures are trapped in caves, they quickly turn down their pigment production and lose all ability to express it within a couple of generations. This is for good reason, as light-absorbing melanins and carotenoids are metabolically costly to produce and actuate into position.
For larger creatures, like smartphones, there are a host of effects that arise to oppose transparency. The lens of the eye for example, needs to burn a non-trivial amount of energy just to maintain transparency. To make a large scale device transparent, the first thing you need is transparency of the smaller parts that comprise them. While this appears rather obvious, it is not enough just to put transparent parts together. The more difficult requirement you need is to have a smooth variation in the refractive indexes across the subcomponents. Fireflies can efficiently emit light through their bodies only by optimising each interphase in the light path as the different tissues are traversed.
There are many kinds of transparent display options available today, and new methods are being developed all the time. One way to do this is to coat two pieces of glass with transparent but conductive material like indium tin oxide (ITO), and sandwich a gel of polarisable molecules between them. When an electric field is applied, the liquid crystal changes its alignment and becomes transparent or non-transparent, depending on the materials used.
The display is not the problem for the Polytron phone which sports an OLED-based liquid crystal device. The problem is several of the smaller components, like the battery and the memory. Transparent lithium-ion batteries have previously been developed based on PDMS. PDMS is a favourite polymer material often used in the life sciences to build transparent microfluidic sensors, and Polytron plans to incorporate these kinds of batteries in future versions of the phone. They will also start using transparent speakers and touchscreens on both sides of the final product.
What can you do with a transparent phone?
Part of the power of having control over transparency is that, not only can you block light, but you can control the properties of the light that you might let pass through it. In addition to simple point pixel effects like colour or polarisation, more complex phenomena like refraction and diffraction might be controlled if the resolution of the device is high enough. Spatial light modulators (SLMs) used in optics can be switched at speeds of several thousand hertz, to create virtually any kind of wavefront that is desired.
Apps that feed the front camera image to the display have been available for some time but are only a crude and artificial attempt at transparency. True transparency would turn a phone into a virtual cuttlefish. The video above shows how the cuttlefish is able to mirror its local environment by directly controlling the pigments in its skin, which are under control of its nervous system. While the cuttlefish can’t become anything it might choose, as it apparently requires the appropriate visual input from the environment to drive the pigment alterations, a phone, at least in principle, could.