Compact chips advance timing for comms, navigation and more

The US National Institute of Standards and Technology (NIST) and its collaborators have created compact chips that seamlessly convert light into microwaves. Described in the journal Nature, the chips could improve the accuracy and quality of technologies that rely on high-precision timing and communication, such as GPS, phone and internet connections, and radar and sensing systems.

The team’s technology reduces something known as timing jitter, which is small, random changes in the timing of microwave signals. Similar to when a musician is trying to keep a steady beat in music, the timing of these signals can sometimes waver a bit. The researchers reduced these timing wavers to a very small fraction of a second — 15 femtoseconds, to be exact — making the signals much more stable and precise in ways that could increase radar sensitivity, the accuracy of analog-to-digital converters and the clarity of astronomical images captured by groups of telescopes.

“There are all sorts of applications for this technology; for instance, astronomers who are imaging distant astronomical objects, like black holes, need really low-noise signals and clock synchronisation,” said NIST physical scientist Frank Quinlan. “And this project helps get those low-noise signals out of the lab and into the hands of radar technicians, of astronomers, of environmental scientists, of all these different fields, to increase their sensitivity and ability to measure new things.”

Significantly, the researchers have taken what was once a tabletop-size system and shrunken much of it into a compact chip, about the same size as a digital camera memory card. Reducing timing jitter on a small scale reduces power usage and makes it more usable in everyday devices.

To accomplish this, the researchers use a semiconductor laser, which acts as a very steady flashlight. They direct the light from the laser into a tiny mirror box called a reference cavity, which is like a miniature room where light bounces around. Inside this cavity, some light frequencies are matched to the size of the cavity so that the peaks and valleys of the light waves fit perfectly between the walls. This causes the light to build up power in those frequencies, which is used to keep the laser’s frequency stable.

The stable light is then converted into microwaves using a device called a frequency comb, which changes high-frequency light into lower-pitched microwave signals. These precise microwaves are crucial for technologies like navigation systems, communication networks and radar because they provide accurate timing and synchronisation.

Right now, several of the components for this technology — such as lasers, modulators, detectors and optical amplifiers — are located outside of the chip, as the researchers test their effectiveness, but the ultimate goal is to integrate all the different parts onto a single chip. This would enable the team to reduce both the size and power consumption of the system, which means it could be easily incorporated into small devices without requiring lots of energy and specialised training.

“The current technology takes several labs and many PhDs to make microwave signals happen,” Quinlan said. “A lot of what this research is about is how we utilise the advantages of optical signals by shrinking the size of components and making everything more accessible.

“The goal is to make all these parts work together effectively on a single platform, which would greatly reduce the loss of signals and remove the need for extra technology. Phase one of this project was to show that all these individual pieces work together. Phase two is putting them together on the chip.”

Image caption: NIST researchers test a chip for converting light into microwave signals. Pictured is the chip, which is the fluorescent panel that looks like two tiny vinyl records. The gold box to the left of the chip is the semiconductor laser that emits light to the chip. Image credit: K Palubicki/NIST.