Researchers Use Silicon Photonics to Create Quantum Random Number Generator

A chip-based device measuring just 1 sq mm has demonstrated the potential to generate quantum-based random numbers at gigabit (Gb)-per-second speeds, using minimal power. The tiny device, which is enabled by silicon photonics, could be used as a stand-alone or in devices such as laptops and smartphones to encrypt data in real time.

Researchers at the University of Bristol have demonstrated a random number generator based on randomly emitted photons from a diode laser. Because the photon emission from the laser is inherently random, it is impossible to predict the numbers that will be generated. The other required optical components of the quantum random number generator (QRNG) are integrated on a millimeter-scale monolithic silicon-on-insulator (SOI) chip.

Researchers created a chip-based device measuring 1 sq mm that can potentially generate quantum-based random numbers at gigabit-per-second speeds. The small square to the right of the penny contains all the optical components of the random number generator. Courtesy of Francesco Raffaelli, University of Bristol.

The device converts the photons that are emitted into optical power using an interferometer. Tiny photodetectors integrated into the chip detect the optical power and convert it into a voltage that can be used to generate random numbers.

Researchers said that only a small amount of light is actually able to reach the photodetectors, because light is lost inside the chip. To mitigate this effect, researchers optimized the parameters and designed low noise electronics to detect the optical signal inside the chip.

For testing purposes, researchers had a foundry fabricate their random number generator chip; and after characterizing the optical and electronic performance of the chip, they used it for random number generation. They estimate a potential randomness generation rate of nearly 2.8 Gb/s for their device — a rate that would be fast enough to enable real-time encryption.

Researcher Francesco Raffaelli said that in addition, random number generation was demonstrated using about one-tenth of the power used in other chip-based quantum random number generator devices.

The new chip-based device is more portable and also more stable than the same type of device made using bulk optics, partly because conditions, such as temperature, are easier to control in a small chip. It is also easier to precisely reproduce thousands of identical chips using semiconductor fabrication techniques rather than bulk optics.

Researchers used an external laser and electronics and measurement tools that required an optical table to demonstrate their QRNG. They are now working to create a portable device about the size of a mobile phone that includes both the chip containing the optical components and the necessary electronics. The team believes that widespread integration of its design in more complex systems could be possible, considering the device’s size; its simple, robust and low-power operation; and the growing use of silicon photonics in industry.

The team says that their QRNG could be directly integrated into silicon devices, such as quantum key distribution (QKD) systems. The team further believes that its QRNG could find applications whenever a low-impact, high rate source of random numbers is required in SOI devices.

“While part of the control electronics is not integrated yet, the device we designed integrates all the required optical components on one chip," said Raffaelli. “Using this device by itself or integrating it into other portable devices would be very useful in the future to make our information more secure and to better protect our privacy.”

The research was published in Optics Express, a publication of OSA, The Optical Society (doi: 10.1364/OE.26.019730).