Smart Windows That Can Encode Data in Sunlight

All digital data transmission comes down to modulating signals. The differences are simply about the transmission medium and the way in which transmitters modulate the data. The most basic implementation is simply modulating an electrical signal carried over a traditional copper wire (or several), which is the basis for everything from USB to HDMI. WiFi does the same thing by modulating and broadcasting a 2.4GHz or 5GHz radio signal. Any wave on the electromagnetic spectrum can carry a modulated signal and that includes sunlight. These special polarized smart windows take advantage of that fact to simultaneously transmit data to an unlimited number of devices in a room.

Polarization is the orientation of transverse waves, which are waves that oscillate perpendicular to the wave’s vector. Polarizer film can block waves in one orientation (like on the XY plane), while allowing others (like on the ZY plane) to pass through unobstructed. This isn’t normally visible to the human eye, but is useful in many applications. An LCD screen, for instance, has two polarizer film layers to let the backlight pass through the actual LCD panel. If you removed the outer polarizer, you wouldn’t be able to see the content on the screen. These smart windows utilize a special polarizer film that only polarizes sunlight when it receives electrical current. By quickly turning that polarizer on and off (modulation), one can encode invisible data in the sunlight that passes through the window.

The benefit here is in the reception. A virtually unlimited number of devices scattered throughout the room can receive that modulated sunlight signal. The devices can then decode the sunlight signal using extremely cheap hardware (basically just a light sensor), which is much more affordable than a conventional radio receiver. The data transmission speed is only limited by two factors: the switching speed of the polarizer and the response time of the light sensor. We already have very fast light sensors (fiber optic systems rely on them), so it comes down to the polarizer speed.

The team behind this smart window technology says that they’ve already achieved 16kbps. Dial-up internet was capable of faster speeds, but this is still enough to transmit useful data to devices for applications like IoT and home automation. The team believes they can increase that to megabits or even gigabits per second. That increased speed would expand the utility of these smart windows.

However, these smart windows have two obvious downsides. The first is that they require sunlight, or at least artificial light shining through the windows. In practice, that means that they probably won’t function at night. The second is that the smart windows can only send data — they can’t receive data. But the low cost and energy efficiency of these smart windows give them tremendous potential.