A Tale Of Two Technologies

By John Oncea, Editor

Two legacy technologies – Ben Franklin’s lightning rod and lithium niobate photonics – are in the news. One because it’s getting a second life, the other because it’s being replaced. Which is which?

Apologies to Charles Dickens.

One’s a colorless solid, the other’s an inanimate rod, one’s insoluble in water, one redirects lightning, one can be doped by magnesium oxide, one requires a connection to earth to perform its protective function, one is grown, one is made of conductive materials, one has hope, one faces despair, one has everything before it, one has nothing before it, one is experiencing a rebirth, one is going direct the other way — in short, lithium niobate is finding a new life in photonics, the lightning rod is fading away, maybe forever.

Whew. Did I lose you? Let’s get this article back on track.

Sooner Or Later, Everything Old Is New Again * (Unless It Isn’t)

The two technologies we’re talking about here – and admittedly I’m using “technologies” a bit loosely – are lithium niobate and the lightning rod. Lithium niobate is making a comeback in the world of photonics while lasers are replacing the lightning rod. So, where do you want to start? Lithium niobate? You got it.

* Dickens and Stephen King in one article? Cool.

Unlocking The Electromagnetic Spectrum With Lithium Niobate

“Lithium niobate, first discovered in 1949, is finding new uses in the field of photonics because unlike other materials it can generate and manipulate electromagnetic waves across the full spectrum of light,” Optics.org quotes The University of Adelaide’s Dr. Andy Boes as saying. Boes and fellow researcher Arnan Mitchell, RMIT University’s Distinguished Professor, are both experienced in developing lithium niobate to harness its “exceptional properties in photonic chips” for new and diverse future applications such as space navigation and more.

Silicon has long been the go-to material for electronic circuits, but its limitations have become increasingly apparent in photonics. “Lithium niobate has come back into vogue because of its superior capabilities and advances in manufacturing mean that the material is now readily available as thin films on semiconductor wafers,” says Boes.

A one-micron-thick layer of lithium is placed on a semiconductor wafer/substrate. Photonic circuits are tailored according to the chip’s intended use and are printed into the layer. “The ability to manufacture integrated photonic chips from lithium niobate will have a major impact on applications in technology that uses every part of the spectrum of light,” said Mitchell. “Photonic chips can now transform industries well beyond optical fiber communications.”

One benefit of using lithium niobate on photonic chips will be allowing for navigation on the moon as there is no GPS available in lunar rovers. “By detecting signals in the infrared part of the spectrum a photonic chip irradiated by a laser can measure movement without needing external signals,” writes Optics.org.

Mitchell adds, “This is not science fiction, it’s happening now, and competition to harness the potential of lithium niobite photonic technology is heating up.”

The Harvard John A. Paulson School of Engineering and Applied Sciences joins the Australians in rediscovering lithium niobate, creating a new chip with a circuit made of the material. “Collaboration with Cristina Benea-Chelmus at the Laboratory of Hybrid Photonics (HYLAB) in EPFL’s School of Engineering, and ETH Zurich, [has allowed for the development] of a new thin-film circuit that, when connected to a laser beam, produces finely tailorable terahertz-frequency waves,” writes Harvard.

“The device opens up a world of potential applications in optics and telecommunications by exploiting the so-called terahertz gap, which lies between about 300-30,000 gigahertz on the electromagnetic spectrum. This range is currently something of a technological dead zone, describing frequencies that are too fast for today’s electronics and telecommunications devices, but too slow for optics and imaging applications.”

And what is allowing that world to be opened? You guessed it – an extremely thin chip with an integrated photonic circuit made of lithium niobate which isn’t only producing terahertz waves but allows for “engineering a solution for custom-tailoring their frequency, wavelength, amplitude, and phase. Such precise control over terahertz radiation means that it can now potentially be harnessed for next-generation applications in both the electronic and optical realms.”

The Lightning Rod Is Dead. Long Live The Lightning Rod!

Now then, what about the lightning rod? Well, it’s been around for almost 250 years and really isn’t going anywhere. But Nature reports a rapidly-firing laser capable of producing 1,000 pulses of light per second has caused lightning bolts to change course high in the Alps, a finding that suggests laser beams could be used as lightning rods to protect infrastructure.

“Physicists have wondered whether lasers could enhance protection because they can reach higher into the sky than a physical structure and can point in any direction,” Nature quotes Stelios Tzortzakis, a laser physicist at the University of Crete who was not involved in the research, as saying. “But despite successful laboratory demonstrations, researchers have never before succeeded in field campaigns.”

A group of approximately 25 researchers set out to change that, creating the Laser Lightning Rod project that tested the high-power laser. The laser was set up next to the Säntis telecommunications tower, a tower frequently struck by lightning.

“A sufficiently intense laser beam can create a conductive path for lightning to travel down, just as a metal wire can,” reports Nature. “Physicists think that it does this by shifting the properties of air so that the beam focuses into a thin, intense filament. This rapidly heats the air, reducing its density and creating a favorable path for lightning. ‘It’s like drilling a hole through the air with the laser,’ says Aurélien Houard, a physicist at the Laboratory of Applied Optics in Paris, who led the project.”

Researchers spent 10 weeks observing and “spotted the laser channeling four lightning events during 6 hours of thunderstorms. A high-speed camera clearly showed one strike following the straight line of the laser beam, rather than taking a branching path.”

“What they’ve done is very impressive,” Scientific American reports Jerry Moloney, an optical scientist at the University of Arizona, who was one of the early pioneers of this laser application but was not involved in the study as saying. “It’s ‘a very, very sophisticated setup.’”

One place where this technology would be particularly useful is airports, Scientific America reports. According to Irene Miller, an assistant professor of aviation at Southern Illinois University, who was not involved in the new study, lightning strikes wreak havoc in the form of flight delays and injuries (even death) to employees and travelers, says.

At present, it’s unclear how laser lightning rod technology might be adapted to airports because even tiny lasers aimed at the sky are notoriously dangerous to pilots. One solution would be to adjust the laser’s wavelength and power, and the study authors hope to explore that idea in future projects, notes Scientific American before concluding, “For now, though, Benjamin Franklin’s innovation will have to do.”