Technique for “phase locking” arrays of tiny lasers could lead to terahertz security scanners.
Terahertz radiation — the band of electromagnetic radiation between microwaves and visible light — has promising applications in security and medical diagnostics, but such devices will require the development of compact, low-power, high-quality terahertz lasers.
In this week’s issue of Nature Photonics, researchers at MIT and Sandia National Laboratories describe a new way to build terahertz lasers that could significantly reduce their power consumption and size, while also enabling them to emit tighter beams, a crucial requirement for most practical applications.
The work also represents a fundamentally new approach to laser design, which could have ramifications for visible-light lasers as well.
The researchers’ device is an array of 37 microfabricated lasers on a single chip. Its power requirements are so low because the radiation emitted by all of the lasers is “phase locked,” meaning that the troughs and crests of its waves are perfectly aligned. The device represents a fundamentally new way to phase-lock arrays of lasers.
In their paper, the researchers identified four previous phase-locking techniques, but all have drawbacks at the microscale. Some require positioning photonic components so closely together that they’d be difficult to manufacture. Others require additional off-chip photonic components that would have to be precisely positioned relative to the lasers. Hu and his colleagues’ arrays, by contrast, are monolithic, meaning they’re etched entirely from a single block of material.
“This whole work is inspired by antenna engineering technology,” says Qing Hu, a distinguished professor of electrical engineering and computer science at MIT, whose group led the new work. “We’re working on lasers, and usually people compartmentalize that as photonics. And microwave engineering is really a different community, and they have a very different mindset. We really were inspired by microwave-engineer technology in a very thoughtful way and achieved something that is totally conceptually new.”
The researchers’ laser array is based on the same principle that underlies broadcast TV and radio. An electrical current passing through a radio antenna produces an electromagnetic field, and the electromagnetic field induces a corresponding current in nearby antennas. In Hu and his colleagues’ array, each laser generates an electromagnetic field that induces a current in the lasers around it, which synchronizes the phase of the radiation they emit.
This approach exploits what had previously been seen as a drawback in small lasers. Chip-scale lasers have been an active area of research for decades, for potential applications in chip-to-chip communication inside computers and in environmental and biochemical sensing. But as the dimensions of a laser shrink, the radiation the laser emits becomes more diffuse. “This is nothing like a laser-beam pointer,” Hu explains. “It really radiates everywhere, like a tiny antenna.”
If a chip-scale laser is intended to emit radiation in one direction, then any radiation it emits in lateral directions is wasted and increases its power consumption. But Hu and his colleagues’ design recaptures that laterally emitted radiation.
In fact, the more emitters they add to their array, the more laterally emitted radiation is recaptured, lowering the power threshold at which the array will produce laser light. And because the laterally emitted radiation can travel long distances, similar benefits should accrue as the arrays grow even larger.
“I’m a firm believer that all physical phenomena can be pros or cons,” Hu says. “You can’t just say unequivocally that such-and-such a behavior is universally a good or bad thing.”
In large part, the energy from the recaptured lateral radiation is re-emitted in the direction perpendicular to the array. So the beam emitted by the array is much tighter than that emitted by other experimental chip-scale lasers. And a tight beam is essential for most envisioned applications of terahertz radiation.
In security applications, for instance, terahertz radiation would be directed at a chemical sample, which would absorb some frequencies more than others, producing a characteristic absorption fingerprint. The tighter the beam, the more radiation reaches both the sample and, subsequently, a detector, yielding a clearer signal.
Hu is joined on the paper by first author Tsung-Yu Kao, who was an MIT graduate student in electrical engineering when the work was done and is now chief technology officer at LongWave Photonics, a company that markets terahertz lasers, and by John Reno of Sandia National Laboratories.
“The use of phased arrays of antennas is widespread in the microwave and allows one to direct radiation in a very narrow beam, in a specific direction,” says Benjamin Williams, an associate professor of electrical engineering at the University of California at Los Angeles. “In the microwave, however, it is straightforward to drive each antenna with the same phase so that all the contributions to the field add up constructively in the far field. It is more complicated to do the same thing using an array of laser emitters, since you can’t easily control the phase of each element. Rather, you must coax each laser emitter to phase-lock with its neighbors through some mechanism. This work has shown a new method to phase-lock large arrays of lasers.”
“The work is also important for addressing an ongoing challenge for terahertz QC [quantum cascade] lasers, namely, how can you generate a high-quality beam with good efficiency?” he adds. “This has traditionally been tough for terahertz QC lasers, since the individual laser cavities are smaller than the wavelength. It turns out that this fact means you can borrow many of the techniques from the microwave — like phased-array antennas. The work shows a high-quality beam with very high slope efficiency in a monolithic surface-emitting package.”
Learn more: New approach to microlasers
The Latest on: Microlasers
via Google News
The Latest on: Microlasers
- These "Microlasers" Turn Infrared into Laser Light, and May Play a Role in Next-Gen Medical Tech on June 27, 2018 at 9:35 am
The biggest, brightest lasers make for good headlines, but this isn’t a story about those. This is a story about lasers so tiny you need a microscope just to see them—lasers smaller than red blood cel... […]
- Scientists Create Continuously Emitting Microlasers With Nanoparticle-Coated Beads on June 18, 2018 at 8:10 am
Researchers have found a way to convert nanoparticle-coated microscopic beads into lasers smaller than red blood cells. These microlasers, which convert infrared light into light at higher frequencies ... […]
- Scientists create continuously emitting microlasers with nanoparticle-coated beads on June 18, 2018 at 8:04 am
A scanning electron micrograph image (left) of a 5-micron-diameter polystyrene bead that is coated with nanoparticles, and a transmission electron micrograph image (right) that shows a cross-section o... […]
- A dash of gold improves microlasers on October 6, 2017 at 2:11 pm
Gold. The word brings to mind wedding rings, buried treasure and California in the 1840’s. But when gold is reduced to 1/100,000 the size of a human hair, it takes on an entirely new personality. By a... […]
- Biocompatible and biodegradable microlasers that can be injected into the human body on April 30, 2017 at 5:00 pm
The goal of InjectableLasers is to make for the first time biocompatible and biodegradable/resorbable microlasers, which could be injected into human body. The lasers proposed here will be made comple... […]
- A new trick for controlling emission direction in microlasers on June 17, 2016 at 6:21 am
Click to share on Facebook (Opens in new window) Click to share on Twitter (Opens in new window) Click to share on Tumblr (Opens in new window) Click to share on LinkedIn (Opens in new window) Click t... […]
- A new trick for controlling emission direction in microlasers on June 16, 2016 at 5:00 pm
Artist's view showing the control of the emission direction of lasing at exceptional points in a whispering gallery mode microlaser. The tori and the spheres represent the microtoroid resonators and t... […]
- Solid-state proteins drive low-threshold microlasers on August 2, 2015 at 5:00 pm
Due to its distinctive structure, a protein from a bioluminescent jellyfish produces very bright solid-state fluorescence and constitutes a good laser gain medium. In Aequorea victoria, the GFP acts a... […]
- Capasso lab demonstrates highly unidirectional 'whispering gallery' microlasers on December 13, 2010 at 7:38 am
Utilizing a century-old phenomenon discovered in St. Paul's Cathedral, London, applied scientists at Harvard University have demonstrated, for the first time, highly collimated unidirectional microlas... […]
- Yale and Bell Labs Use Chaos Theory to Make Microlasers 1,000 Times More Powerful than Conventional Counterparts on January 1, 2001 at 3:59 am
Using chaos theory, a team of scientists from Yale University, Lucent Technologies’ Bell Labs, and the Max Planck Institute of Physics in Germany have demonstrated novel semiconductor microlasers with ... […]
via Bing News