As any smartphone aficionado knows, the accelerometer is one of the key sensors within the device – it allows the phone to know when and by how much it’s been moved. Accelerometers also have many other applications, being major components of things like navigation systems, various automotive systems, and image stabilization systems in cameras. Now, researchers from the California Institute of Technology are developing a laser-based accelerometer, that they claim should offer much better performance than is currently possible.
Most often, accelerometers work by using an electrical circuit to gauge tiny movements of something known as a proof mass. The proof mass is flexibly mounted to the accelerometer, so acceleration in any direction causes it to move. In the experimental Caltech accelerometer, however, that circuit is replaced with laser light.
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On a silicon microchip, the scientists created a tiny “optical cavity” measuring around 20 microns in length, a single micron in width, and with a thickness of a few tenths of a micron. Within that cavity are two parallel rail-like silicon “nanobeams,” that guide laser light as it enters the cavity. That light is guided to a point where it is made to bounce back and forth across the gap between the two beams.
The accelerometer’s proof mass is attached to one of the nanobeams. When that mass moves, it causes the size of the gap between the beams to change. This in turn affects the intensity of the laser light coming out of the optical cavity. The accelerometer is able to detect incredibly small amounts of movement, by analyzing those changes in intensity.
Just how sensitive is it? According to Caltech, it can register proof mass movements “as small as a few femtometers (roughly the diameter of a proton).” Such tiny movements obviously don’t take very long to occur, but the accelerometer is up to the task. It is reportedly “sensitive to motions that occur in tens of microseconds, thousands of times faster than the motions that the most sensitive sensors used today can detect.”
Before the technology can see common use, however, engineers still have to figure out how to cost-effectively integrate lasers and the associated optics into silicon microelectronics.
A paper on the research was recently published in the journal Nature Photonics.