Pulsed Laser Innovations Power Nobel-Winners’ Research
When Neil Armstrong took his first steps on the Moon, the video and his first words—transmitted across nearly 240,000 miles and broadcasted around the world—were instantly famous.
These days we take for granted that astronauts can post tweets from orbit and data can stream back from across the solar system. We see high-definition images of Pluto taken by a spacecraft over three billion miles away and monitor the progress of the Curiosity rover on the surface of Mars.
But all that information has to travel to Earth—and as the quantity and quality of the instruments being sent into space get better and the sheer number of spacecraft is growing, the amount of data is only getting bigger and bigger.
In short, we need more bandwidth. And right now, it looks like the answer is lasers.
That’s where Malcolm Wright’s group at the Jet Propulsion Laboratory (JPL) comes in. For the last 20 years, he’s been working on developing the technology to build optical communications into spacecraft.
If that sounds a little familiar, you’re not wrong. We already use optics—usually fiber optics—for high-definition cable television, telephone lines, and high-speed Internet access. And in fact, Wright says his team’s goal was to find existing laser-based telecommunications infrastructure that could be adapted for space communication.
Today, ground-to-space communications are typically transmitted through microwave-frequency radio waves. The amount of data you send in a given time is governed by the length of the wave, Wright explains, with shorter wavelengths able to pack in more information.
Lasers transmit light waves, which have a much higher frequency. They also focus the light a lot more precisely than radio transmitters do, Wright says. “Radio communications energy spreads out. But with a laser, all that light can be concentrated on a small spot. That means, for a small amount of transmitted power, we can get a stronger signal back on Earth.”
That’s a big part of the reason optics have been so successful in telecommunications on the ground too. But space-to-ground was going to require some pretty important modifications. For one thing, in fiber optics, the fiber acts as a guide for the laser, Wright explains, so no light is lost from transmitter to receiver. But you can’t run a fiber from the International Space Station to the ground, let alone from Mars or the further reaches of the solar system.
Laser beams can still travel those long distances, he says, but the beam will diverge somewhat, diminishing how much signal reaches the receiver. That means the system needs to start off with more power.
The other difference is in how the information is transmitted over extremely long distances, say from the Moon or deep space to Earth. Transmitters use very short but very high-powered pulses, explains Wright, rather than transmitting continuous streams of ones and zeroes. “It’s very data-efficient. You don’t need a lot of signal to determine when a bit comes.”
These pulses need to be extremely fast to avoid over-taxing the laser—and to avoid the need for a very power-hungry laser. “The average power requirement is not too demanding, around a few watts, but peak power might be up to a kilowatt,” Wright says. “All that energy but only for a short amount of time.”
For communications, Wright was looking for lasers capable of nanosecond pulses—pulses that last just a billionth of a second.
For that, he turned to a San Jose, California-based PolarOnyx. “Their expertise was in making these lasers support very high peak powers,” Wright says.
PolarOnyx had built its expertise in telecommunications lasers and received Phase I and II Small Business Innovation Research (SBIR) contracts from JPL in 2002 to develop short-pulse fiber lasers for optical communications from space. (Unlike with fiber-optic telecommunications, the fiber in this case refers to how the laser pulse is generated and amplified, rather than how it travels.)
Since those JPL contracts, PolarOnyx Inc. has received additional SBIR funding from Goddard Space Flight Center, Langley Research Center, and JPL to continue developing fast-pulsed lasers and amplifiers.
Company founder Jian Liu says the company has benefited tremendously from the SBIR funding. “Through those projects, we have developed several key technologies for the fiber laser project.” Among other advances funded by the SBIR contracts, he says, was the ability to scale up a laser’s power to 100 watts while managing thermal issues and others that could damage equipment at high power.
So far, the company has delivered several laser systems to NASA under the SBIR funding, including a few recent 20-watt lasers that can pulse at nanosecond rates with repetition rates up to 100 megabits per second. Wright says these projects have not been for specific space missions. “This is more like, show me the capability so when the project comes along we can say, hey, we can do this.”
However, he says, looking forward he can see applications in the next generation of upcoming space communication projects. “What we use right now, you can get six megabits per second from Mars using radio frequencies. And we would be pitching from 30 to 100 megabits per second using laser communications.”
But in the meantime, Liu says the laser systems designed thanks to SBIR funding are already finding plenty of customers on the ground.
PolarOnyx spun off a subsidiary, called Laser-Femto, to commercialize the fiber laser systems like those developed with SBIR funding, and Liu says they have found a solid market among research institutions, including well-known universities such as Howard, Yale, Stanford, and more. The Army and Air Force research labs are also customers.
Among other selling points, the company took the work it did for NASA and improved it by building it into femto-pulsed lasers. While nanosecond pulses last a billionth of a second, femtosecond pulses are orders of magnitude faster, lasting a quadrillionth of a second.
“We are the leading company in ultra-fast pulsed fiber laser in this field. We are able to offer the highest energy and the highest power and the shortest pulse in a fiber laser,” Liu says, adding that the company has sold more than 400 lasers since around 2005.
The company has won multiple awards for its “first-to-market” femtosecond fiber laser products. And being first positioned them well for the most cutting-edge research, Liu notes, in fields such as physics, materials processing, and biomedical science. “Our lasers have supported three Nobel Prize winners,” he boasts.
Most recently, Donna Strickland won in 2018 for “groundbreaking inventions in the field of laser physics.” Although the Nobel-winning research was published in 1985, Strickland has used PolarOnyx lasers in her more recent work: the company notes that Strickland bought her first system from Laser-Femto back in 2006 and has been a loyal customer ever since.
Liu says the NASA funding has been instrumental in the company’s success, particularly in staying ahead of low-cost competitors. “We had to keep innovating to stay ahead of the market,” he explains. “The NASA funding enabled us to do that—so we could move faster than every competitor.”