Scientists use light to flick nanoswitch
Light bending Mechanical memory for optical circuits is a step closer, after US scientists successfully buckled nano-sized particles of silicon using laser light, and observed for the first time, the predicted zero-frequency singularity.
The mechanical optic switch, which appears in the journal Nature Nanotechnology, has the potential to form a new type of computer memory that stores data at room temperature, without power and is immune to electromagnetic noise.
Dr Hong Tang, from Yale University, says using a new technique, the researchers were able to buckle a beam of solid silicon using laser light further than previously possible.
"We actually moved [the beam] more than 200 or 300 nanometres," he says. "The beam itself is only a hundred nanometres, so we moved it three times the size of the structure itself. Before that, we could only move it a couple of nanometres."
The beams, which buckle like a deck of playing cards, can be used to encode data in a binary system of buckled ups and downs. Once cooled, the beam retains its shape.
To buckle the beam, laser light enters an optical cavity, and builds up at a resonance frequency, like sound does inside a flute. The optical cavity is coupled to a mirror-like mechanical resonator, which is the beam. When light photons bounce off the 'mirror', they push the beam back. This light-triggered mechanical movement is the field of optomechanics.
Previously, scientists have used extreme temperatures to buckle silicon, but this is the first time it has been done at room temperature.
By pumping more energy into the resonator results in more movement, but there's a catch.
Whenever the mirror moves back, the space inside the optical cavity changes and so does the resonance frequency. Incoming light must adjust to match.
Tang says its similar to pushing a child on a swing.
"The more you push, the higher the kid can swing, so you gain energy," he says. "But at a certain point, as they swing higher, the swing becomes slower."
"If you push at the same frequency you pushed before, you are actually out of sync with the intrinsic frequency of the swing, so instead of adding energy into the swing you are actually taking energy out of it."
It's the same with the resonator. To get around this problem, incoming light was adjusted in real-time by sourcing it from an optical field, rather than an electrical one.
First evidence of slow-down
The researchers were also able to slow the resonator and observe the theoretical zero-frequency singularity.
Buckled beams are very stable; on an energy graph each state is a deep well of low energy with a huge high-energy hill between them.
"Imagine that when you hit the top of the hill between two double wells, the kinetic [moving] energy of the mechanical resonator changes to potential [stored] energy," says Tang.
"You don't have kinetic energy anymore, so the frequency goes to zero. It means the mechanical resonator becomes extremely slow."
Once the frequency drops to zero, the mechanical resonator can be tuned to a large range of different frequencies.
"By slowing down, we can tune them to almost a hundred per cent (instead of two per cent), which is very important."
Tang this study could lead to configurable optical circuits and mechanical memory immune to noise. But one major challenge to overcome is the huge amount of energy currently needed to make the switches.
"I think the result is innovative and clever," says physicist Dr David Reilly of the University of Sydney, who was not involved in the study.
"It has advantages over conventional memory in computers and phones which is electromagnetic, and susceptible to electromagnetic noise," says Reilly.
This gives it an edge in varied applications like defense, satellites and MRI machines; anywhere with a high potential for electromagnetic interference, he says.
"If you wanted an information technology that could withstand a nuclear blast, this comes to mind."