Laser sight

 by D.H. | London

DIGITAL photography has made the creation of two-dimensional images a trivial task. Adding a third, however, is still expensive. The traditional approach is stereoscopy, which combines two or more flat pictures taken from different angles, to create an illusion of depth in a way similar to that which the brain employs in processing the different perspectives seen by the left and right eyes. The problem with this method is that, like the brain, it is subject to optical illusions. Separating objects of interest from the background, and shadows from holes, is hard. So is determining distances precisely.

An alternative—and in many ways better—approach is lidar. Light detection and ranging (by analogy with radio detection and ranging, or radar) sweeps a laser beam over the field of view. By recording how quickly reflections return from different places, a lidar knows exactly how far away they are. The result can then be used by, for example, a robot that wishes to move around in that environment.

Lidar, however, has two problems: it is bulky and it is expensive. But engineers at Vescent Photonics of Denver, Colorado, hope to change this. They have developeda lidar that they think can be shrunk to the size of a box of matches and which will, according to Scott Davis, one the firm’s co-founders, cost hundreds, rather than thousands of dollars if mass produced.

Existing lidars sweep the beam mechanically, and this mechanism takes up space. Vescent has managed to replace these moving mechanical parts with a solid-state beam-steering system. The Steerable Electro-Evanescent Optical Refractor (SEEOR), as the company dubs its invention, sends the laser beam along a glass waveguide that has a special liquid-crystal cladding. Most of the light passes through the glass but part of it, known as the evanescent wave, skims the surface of the liquid crystal. And that allows the whole beam to be manipulated.

One property of liquid crystals is that applying a voltage to them changes their refractive index—that is, the speed of light passing through them. This, in turn, causes the light’s angle of travel to shift. Altering the voltage across the liquid crystals in a SEEOR thus instantly shifts the direction of the emerging beam.

Vescent is not the first outfit to come up with the idea of using liquid crystals to manipulate a lidar beam, but previous attempts to do so have managed to move the beam only a degree or so. SEEOR can scan a beam horizontally over an angle of 60°, and vertically over 20°, thanks to the use of a special liquid crystal, whose refractive index is particularly sensitive to changes in voltage, and also by the perfection of the evanescent-wave approach (previous prototypes sent the whole beam through the liquid crystal, which is less efficient).

Dr Davis thinks that is just the start. He is confident the next version of SEEOR will be able to sweep 120°, both vertically and horizontally. Its range will increase, too, from a few hundred metres to several kilometres. And its size, currently that of a paperback book, will shrink to that of a pack of cards – and ultimately to that of a matchbox.

Vescent’s first customer is likely to be the American armed forces. They have helped pay for SEEOR’s development, and they plan to use it to provide electronic eyes for various types of small robots, including aerial drones and unmanned ground vehicles.

Civilian applications should follow soon, though. Lidar is already widely used for surveying and mapping. Vescent hopes to obtain part of that market. The firm also has its sights on the collision-avoidance systems installed in top-of-the-range cars. At the moment, these employ radar. But lidar is more accurate, and it is also immune to interference from other electrical equipment. Moreover, if the visionaries of automobile automation have their way, collision-avoidance is just the start. The end will be self-driving cars—civilian versions of the robotic vehicles the army would like to build. That would be a huge market for lidar, if it ever came to pass.

More prosaically, cheap, compact lidars should have applications in manufacturing and other tasks requiring accurate measurement. They might also be useful in security systems.

Dr Davis even sees non-sensory applications, for steerable beams are useful in communications too. They might, for example, be fitted to miniature satellites, known as cubesats. These are cheap to launch but are currently restricted in their ability to talk to the ground because their radio transmitters have a capacity of only a few kilobits per second. Vescent’s system, by contrast, can manage megabits—in a laboratory, at least.

Eventually, Dr Davis hopes, beamsteerers will be small enough to fit into devices like smartphones, improving both their ability to communicate and the quality of any pictures they are used to take. Existing camera phones have already transformed people’s attitude to photography. Add a third dimension, and who knows what will happen? economist