Micro-LEDs boost random number generation

Miniature LEDs called micro-LEDs have been shown to generate random numbers at gigabit-per-second speeds by a team of researchers from Saudi Arabia and the United States^[1].

The generation of random numbers is vital for many tasks, including data security — where it is used to create encryption keys and passwords — and computer simulations of complex systems such as the weather and financial markets.

There is, therefore, a strong demand to develop cost-effective random number generators that are small enough for chip-scale integration while also offering a fast generation rate.

The most robust and reliable way to generate true random numbers is to sample and digitize a physical process underpinned by the intrinsic randomness of quantum mechanics. For example, the thermal noise, chaos, and jitter from electronic and optoelectronic devices have all been investigated in the past.

Now, Heming Lin, Boon Ooi, and coworkers from KAUST, King Abdulaziz City for Science and Technology (KACST), and the University of California at Santa Barbara report that intensity fluctuations in the spontaneous emission from blue GaN micro-LEDs, ranging in size from 5-100 μm, can serve as a quantum random number generator (QRNG) with an ultra-high generation rate of 9.375 Gbit/s.

“Micro-LEDs are compact, reliable, and cost-effective,” say Lin and Ooi. “They consume less power and require simpler electronic and photonic system architectures than other competing technologies.”

The idea of using LEDs to generate numbers is not new. Over the past decade, research teams have explored measuring photon number and arrival time. However, a major limitation of these previous schemes is that they have provided much slower generation rates, typically on the scale of no more than a few hundred megabits per second.

“Systems relying on single-photon detection typically extract only two bits per sampling cycle, whereas our system achieves six bits by leveraging intensity fluctuations,” explain Lin and Ooi.

Importantly, for any QRNG to be trusted, its output must be stringently tested to ensure it is sufficiently random. The tests developed by the U.S. National Institute of Standards and Technology (NIST) are the gold standard. The KAUST team tested a variety of micro-LEDs with different sizes — spanning from 5 × 5 μm² to 100 × 100 μm² — and drive currents ranging from 0.5 to 100 mA. All passed the NIST tests.

The team’s future work will focus on boosting generation rates by creating 2D arrays of micro-LEDs that enable parallel random number generation.

The researchers are also planning to create a fully integrated system, rather than using discrete components. At present, the KAUST system comprises a GaN micro-LED, which is temperature stabilized using a thermoelectric cooler and has its light emission fed to an avalanche photodetector. This, in turn, is connected to a sampling oscilloscope via an electronic amplifier.

Lin and Ooi add:“Our next step is to integrate an on-chip photodetector with the micro-LED and subsequently incorporate all the required electronic components to realize a fully integrated QRNG chip.”