It’s clear as glass

By integrating microscopic ducts into the glass that screens are made of, researchers have developed an amazing interface
Marc-André Sabourin
Electronic engineering
An conceptual image of a finger touching a free-floating screen, with action icons streaming out the back.

There’s no point in asking to see Jérôme Lapointe’s invention. “It’s invisible — that’s the innovative part!,” says the engineering physics Ph.D. student at Polytechnique Montréal. His large fingers hold a thin sheet of “Gorilla Glass,” the ultra-strong glass used to make screens for our phones and tablets. To the naked eye, the glass is perfectly transparent, but it actually contains dozens of ducts, each one a third of the width of a human hair, which make it a surprisingly versatile interface.

Touch the glass with your fingertip, and it reads your body temperature. Place a drop of liquid on it to measure the liquid’s refractive index. These are only two examples of the many applications made possible by the light circulating in the ducts, also known as waveguides. “They’re a kind of circuit, only with photons instead of electrons,” explains Lapointe.

The 32-year-old researcher became interested in optical physics because of his colour-blindness. During his studies, he also invented an ocular prosthesis with an artificial pupil that reacts to ambient light, making it much more lifelike than a regular glass eye. His dream, however, is to create transparent screen-computers like those in sci-fi movies. His invisible waveguides are the first step towards that goal.

On their own, the waveguides are nothing new. Researchers were engraving them in glass using lasers back in 1996. But that method had the downside of leaving thin white lines that looked like scratches, and most importantly, the light losses were too great for most applications, so the technology was shelved.

Lapointe was confident he could do better and teamed up with Polytechnique Montréal physics and electrical engineering professor Raman Kashyap. The Ph.D. student gives an example: “When you break a wine glass while doing the dishes, the pieces are difficult to find because light is deflected in a similar way by both the glass and the water.” That is the phenomenon the two men wanted to reproduce using waveguides and Gorilla Glass.

The waveguides are sculpted using a laser beam whose point of focus is inside the glass, leaving the surface intact. The researchers studied the interaction between lasers and matter and found a way to polish the ducts’ walls, thus reducing the amount of light deflected.

Then came the time to perform tests. Lapointe spent two years tweaking and optimizing the laser beam’s parameters: “I must’ve run about 10,000 tests!” His efforts bore fruit — the waveguides he and Kashyap created are not only invisible to the naked eye, but also 10 times more efficient than the best ones made to date.

This feat would probably not have been possible on any other type of glass than Gorilla Glass. Its density and strength, which make it popular for electronics, were perfect for making waveguides. “These properties reduce losses and allow us to sculpt ducts just a few microns below the surface without any breakage.”

The invention has attracted the attention of many phone and tablet manufacturers, including South Korean giant Samsung. “Space is a huge constraint for these companies,” mentions Lapointe. Waveguide-infused screens being perfected opens up a new playground for them — a whole continent of possibilities to explore.

We shouldn’t expect to see interactive glass in the next iPhone, though, or even the one after that. To be functional, each waveguide must be connected to a light source and a detector. These conditions are much easier to set up in a photonics lab than in a phone! Several multinationals have invited Lapointe to come solve this challenge under their roof, but the young man declined, preferring to start his own business in Quebec to develop his discovery and market it someday.

Until that day comes, the inventor can dream as he looks at his smart-phone screen, on which he drew a waveguide for fun. The guide serves no purpose, but it is definitely invisible.

This article was translated from its original, which appeared in French in the January/February 2016 issue of Quebec Science magazine.