New microchip developed using two Nobel Prize-winning techniques

Physicists at the Delft University of Technology have built a new technology on a microchip by combining two Nobel Prize-winning techniques. This microchip could measure distances in materials at high precision, for example underwater or for medical imaging. Because the technology uses sound vibrations instead of light, it is useful for high-precision position measurements in opaque materials. The instrument could lead to new techniques to monitor the Earth’s climate and human health. The research findings have been published in Nature Communications.

The microchip mainly consists of a thin ceramic sheet that is shaped like a trampoline; this trampoline is patterned with holes to enhance its interaction with lasers and has a thickness about 1000 times smaller than the thickness of a hair. As a former PhD candidate in Richard Norte’s lab, Matthijs de Jong studied the small trampolines to determine what would happen if a simple laser beam was pointed at them. The trampoline’s surface started vibrating intensely — by measuring the reflected laser light from the vibrating surface, the team noticed a pattern of vibrations in the shape of a comb they hadn’t seen before. They realised that the trampoline’s comb-line signature functions as a ruler for precision measurements of distance.

This new technology could be used to measure positions in materials using sound waves. The technology does not need any precision hardware and is therefore easy to produce. Norte said it only requires the insertion of a laser, and nothing else. “There’s no need for complex feedback loops or for tuning certain parameters to get our tech to operate properly. This makes it a very simple and low-power technology that is much easier to miniaturise on a microchip. Once this happens, we could really put these microchip sensors anywhere, given their small size,” Norte said.

The new technology is based on two unrelated Nobel Prize-winning techniques, called optical trapping and frequency combs. Norte said that both of these concepts are typically related to light, but these fields do not have any real overlap. “We have uniquely combined them to create an easy-to-use microchip technology based on sound waves. This ease of use could have significant implications for how we measure the world around us,” Norte said.

When the researchers pointed a laser beam at the tiny trampoline, they realised that the forces that the laser exerted on it were creating overtone vibrations in the trampoline membranes. These forces are called an optical trap, because they can trap particles in one spot using light.

“This technique won the Nobel Prize in 2018 and it allows us to manipulate even the smallest particles with extreme precision. You can compare the overtones in the trampoline to particular notes of a violin. The note or frequency that the violin produces depends on where you place your finger on the string. If you touch the string only very lightly and play it with a bow, you can create overtones; a series of notes at higher frequencies. In our case, the laser acts as both the soft touch and the bow to induce overtone vibrations in the trampoline membrane,” Norte said.

Optical frequency combs are used in labs for very precise measurements of time and to measure distances. Due to the importance to measurements in general, optical frequency combs were given a Nobel Prize in 2005. The researchers made an acoustic version of a frequency comb, made out of sound vibrations in the membrane instead of light. “This technology could for example be used for precision measurements underwater to monitor the Earth’s climate, for medical imaging and for applications in quantum technologies,” Norte said.

Image caption: Artist’s impression of the trampoline-shaped sensor. The laser beam passes through the middle of the trampoline membrane creating the overtone vibrations inside the material. Image credit: Sciencebrush