A breakthrough in the development of waveguide technology could extend the reach of light signals to support long-range laser communications and environmental monitoring in the upper atmosphere and beyond, reports new research from scientists at the University of Maryland.
Known as an “air waveguide,” the new technology acts much like a fiber-optic cable, guiding light beams over long distances without a loss of power. Traditional fiber consists of a transparent glass core encompassed by a cladding material with a lower refractive index that reflects light inward; similarly the air waveguide’s core is made of high-density air contained within a “wall” of lower-density air with a similarly lower refractive index.
However, unlike traditional fiber, which requires physical support and can only handle a limited amount of power and therefore distance, the virtually weightless air waveguide could push light beams further, say the U-Maryland researchers.
According to a press release from the University of Maryland, Howard Milchberg, a professor of physics and electrical and computer engineering; physics graduate students Eric Rosenthal and Nihal Jhajj; and associate research scientist Jared Wahlstrand used an air waveguide to conduct light from a spark to a detector approximately a meter away.
The air waveguides are created using extremely short but powerful laser pulses that collapse into a narrow beam known as a filament. These high-speed filaments heat up the air as they travel, Milchberg explains, causing the air to expand and reveal a “hole” of low-density air with a lower refractive index than the surrounding air.
The experiment yielded a strong enough signal—1.5 times more powerful than an unguided signal—to analyze the chemical composition of the air that was initially broken down with a laser to create the spark. Extrapolated over a larger distance, the signal enhancement could be much greater, say the researchers. In addition, because the waveguides are long-lasting, a single waveguide could both send out a laser and collect a signal.
“It’s like you could just take a physical optical fiber and unreel it at the speed of light, put it next to this thing that you want to measure remotely, and then have the signal come all the way back to where you are,” Milchberg said.
Milchberg hopes to soon demonstrate that the air waveguides can be used over distances of 50 meters of more, which could allow the technology to be used for a myriad of measuring applications in which easy access is limited, such as the upper atmosphere or nuclear reactors. The waveguides could also be used for LIDAR, a remote sensing method that uses light instead of radio waves to develop high-resolution topographic maps.
The research paper, “Collection of Remote Optical Signals by Air Waveguides,” is published in the journal Optica. The research was supported by the U.S. Air Force Office of Scientific Research, the Defense Thread Reduction Agency and the National Science Foundation.
