Breakthroughs in Laser Research

Since the fiber industry relies on laser technology, I periodically look to see the latest breakthroughs and news in the field of laser research.

Beaming Lasers Through Tubes. Luc Thévenaz and a team from the Fiber Optics Group at the École Polytechnique Fédérale de Lausanne in Switzerland have developed a technology that amplifies light through hollow-tube fiber cables.

Today’s fiber has a core of solid glass. As light moves through the glass, the light signal naturally loses intensity due to impurities in the glass, losses at splice points, and light that bounces astray. Eventually, the light signal must be amplified and renewed if the signal is to be beamed for great distances.

Thévenaz and his team reasoned that the light signal would travel further if it could pass through a medium with less resistance than glass. They created hollow fiber glass tubes with the center filled with air. They found that there was less attenuation and resistance as the light traveled through the air tube and that they could beam signals for a much greater distance before needing to amplify the signal. However, at normal air pressure, they found that it was challenging to intercept and amplify the light signal.

They finally struck on the idea of adding pressure to the air in the tube. They found that as air is compressed in the tiny tubes that the air molecules form into regularly spaced clusters, and the compressed air acts to strengthen the light signal, similar to the manner that sound waves propagate through the air. The results were astounding, and they found that they could amplify the light signal as much as 100,000 times. Best of all, this can be done at room temperatures. It works for all frequencies of light from infrared to ultraviolet and it seems to work with any gas.

The implications for the breakthrough is that light signals will be able to be sent for great distances without amplification. The challenge will be to find ways to pressurize the fiber cable (something that we used to do fifty years ago with air-filled copper cable). The original paper is available for purchase in nature photonics.

Bending the Laws of Refraction. Ayman Abouraddy, a professor in the College of Optics and Photonics at the University of Central Florida, along with a team has developed a new kind of laser that doesn’t obey the understood principles of how light refracts and travels through different substances.

Light normally slows down when it travels through denser materials. This is something we all instinctively understand, and it can be seen by putting a spoon into a glass of water. To the eye, it looks like the spoon bends at that point where the water and air meet. This phenomenon is described by Snell’s Law, and if you took physics you probably recall calculating the angles of incidence and refraction predicted by the law.

The new lasers don’t follow Snell’s law. Light is arranged into what the researchers call spacetime wave packets. The packets can be arranged in such a way that they don’t slow down or speed up as they pass through materials of different density. That means that the light signals taking different paths can be timed to arrive at the destination at the same time.

The scientists created the light packets using a device known as a spatial  light modulator which arranges the energy of a pulse of light in a way that the normal properties if space and time are no longer separate. I’m sure like me that you have no idea what that means.

This creates a mind-boggling result in that light can pass through different mediums and yet act as if there is no resistance. The packets still follow another age-old rule in Fermat’s Principle that says that light always travels to take the shortest path. The findings are lading scientists to look at light in a new way and develop new concepts for the best way to transmit light beams. The scientists say this feels as if the old restrictions of physics have been lifted and has given them a host of new avenues of light and laser research.

 The research was funded by the U.S. Office of Naval Research. One of the most immediate uses of the technology would be the ability to communicate simultaneously from planes or satellites with submarines in different locations.  The research paper is also available from nature photonics.