Eyeglasses inspire blind-spot-free car mirror

Ashley N. Rice, ashley.rice@photonics.com

Progressive adaptive optics technology used in bi- and trifocal vision correction has been applied to a prototype automobile side mirror that has no blind spot and that does not distort images.

In North America, only passenger-side mirrors can have a “fish eye”-type wide-angle distortion that causes objects in the mirror to appear smaller and farther away than they actually are; driver’s-side mirrors are required to be flat and distortion-free. These flat mirrors provide a more accurate assessment of the nearness of other vehicles, but they also lose sight of cars that enter into the driver’s blind spot.

To remedy this, Hocheol Lee and Dohyun Kim of Hanbat National University and Sung Yi at Portland State University looked to progressive optics.

These images demonstrate the performance differences between the aspheric and progressive mirror (top) and the flat and progressive mirror (bottom). In (a), the standard aspheric mirror is shown with a blue line to indicate the boundary between the two zones. This illustrates the distortion between them. In (b), the progressive prescription developed by researchers at Hanbat National and Portland State universities demonstrates the improved transition between zones, eliminating the blind spot while still giving an undistorted view of objects at a distance. (c) This is the standard flat side-view mirror compared with (d) the wider field of view of the progressive mirror.

“Like multifocal glasses that give the wearer a range of focusing abilities from near to far and everything in between, our progressive mirror consists of three resolution zones: one for distance vision, one for close-up viewing and a middle zone making the transition between the two,” Lee said. “However, unlike glasses, where the range of focus is vertically stacked [from distance viewing on top to close-up viewing on bottom], our mirror surface is horizontally progressive.” The result is a mirror with no blind spot.

The horizontal progressive mirror does have some distortion, but the researchers believe it’s a positive trade-off for the benefits offered. It has more than double the field of view of a traditional flat mirror, and they believe that its manufacturing cost is cheaper than conventional ones with added wide-angle lenses.

“Right now, we just need an empirical prescriptionlike design to permit a binocular disparity and an astigmatism,” Lee told Photonics Spectra.

Lee said that he hopes the mirror will be installed by car makers for safer driving as soon as possible. For this to happen in the US, new regulations will have to be introduced. Also, “manufacturing techniques to bend the glass plate will need to be improved a little,” he said.

The mirrors are now ready for mass production, Lee said, and the research team is looking for distributors.

The findings were published in Optics Letters (doi: 10.1364/OL.38.000317).