OLED-power link jumps from useless 50Mb / s to useful 1Gb / s, Ars Technica

That expense comes from the fact that their light sources, even light-emitting diodes (LEDs), combined with the Components required to imprint information on the light (called modulators), are expensive. Many of you will be thinking “Chris, you’ve finally lost your last marbles, LEDs are cheap as chips.” And you are right, especially when it comes to organic light emitting diodes (OLEDs). The issue is that OLEDs cannot be directly modulated at high speed. Indeed, up until now, the fastest reported data transfer rate via a modulated OLED was a paltry . 6Mb / s. Compared to even my own home network, this is simply too slow to be worthwhile. But, all that is now ready to change, as OLEDs capable of modulating data at more than 1Gb / s have been demonstrated. Organic electrons don’t hurry What makes an OLED so pathetically bad for communication purposes? Essentially (although it is more complicated than this), the OLED has to change its brightness very rapidly. To give a simple example, a binary one might correspond to a bright setting, and a binary zero a dark setting. A string of ones and zeros is sent by flashing the OLED on and off. The speed at which the OLED can change brightness is given by two properties. One is the speed with which electrons transit the organic molecule that comprises the LED. This is typically slow because the electron has to hop from site to site in a kind of random, drift-like fashion. The second is that the OLED structure is like a capacitor that has to charge and discharge. So, the OLED electrodes charge up, then the capacitor slowly discharges by electrons drifting through the OLED molecules. All that’s very slow. To get around these problems, a team of researchers started examining how they might optimize the speed at which the OLED responds . The capacitance was the obvious place to start: by reducing the area of ​​the OLED, the capacitance is reduced. Over the course of three generations, the researchers played with ever-decreasing OLED sizes. However, each reduction in area comes at a cost: the amount of light emitted by the OLED goes down since there are fewer molecules sandwiched between the electrodes. In the course of their experiments, the researchers noted that they could not increase the voltage applied to the OLED above about 5V without destroying it. They found that this was not an intrinsic problem with the light-emitting molecules; Instead, the whole diode got too hot and self destructed. That self-destruction is limiting, as the speed with which electrons are driven through the diode is dependent on the voltage. Higher voltages allow for faster switching times.

To allow for faster switching, the researchers started using a silicon substrate in place of glass to transfer heat away from the diode, allowing them to raise the voltage without wrecking everything. To further reduce the switching time, researchers looked for ways to reduce the resistance of the electrodes themselves. OLEDs make use of transparent electrodes made from indium tin oxide, a material with high resistance. This was replaced with a thin layer of silver, while the bottom electrode, which doesn’t need to be transparent, was made from a (comparatively) thick layer of aluminum. In addition, resistance was reduced by running multiple tracks to each electrode. Finally, the researchers changed the chemistry of the OLED by mixing two organic materials, which provided a faster response. These optimizations resulted in a bandwidth in excess of a (MHz.) Blink faster Now, in the modulation scheme I described above, 728 MHz would not be enough bandwidth for a 1Gb / s link. However, no one uses such a simple scheme. The researchers used modern modulation techniques to encode much more data within a small bandwidth (the scheme they used is a subspecies of orthogonal frequency division multiplexing, which is used in most modern devices). By combining this with error correction schemes, they got the data rate up to 1.1Gb / s over a distance of 2m.

The big benefit of OLEDs is that they are cheap and very flexible: you can print an OLED on almost any surface as long as you can connect electrodes. So, if you have a single-use medical diagnostics that requires a light source, an OLED is your best option. Unfortunately, the slow switching of OLEDs means that many applications remain pipe dreams.

This research helps with that somewhat, although not as much as you might think. The big issue remains the heat dissipation. By moving to a silicon substrate (or, indeed, any crystalline substrate), the researchers immediately limited the flexibility of their OLEDs. It is no longer easy to print the OLED on anything. The substrates will make the OLED a bit more expensive, too, undermining the other big benefit of OLEDs. However, for communications, this is definitely the right direction to be going. And, here I don’t just mean between nodes in a data center, but also within-device communication for applications where both expense and speed matter. Unfortunately, the researchers still have a ways to go: DDR5 runs at over (Gb / s, and fast ethernet is already at over) (Gb / s.) Nature Communications, , DOI:

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