Integrated laser platform: A single chip generates narrow linewidth and tuneable visible light covering all colours. (Courtesy: Myles Marshall/Columbia Engineering)

Researchers in the US have created the first high-performance, tuneable and narrow-linewidth visible-light lasers that are small enough to fit on a photonic chip. Developed by a team at the Columbia University School of Engineering and Applied Science, the new lasers operate at wavelengths shorter than the red part of the electromagnetic spectrum and could be employed in technologies such as quantum optics, bioimaging and laser displays.

“Until now, lasers with performance similar to ones we have developed were benchtop-sized and expensive, which made them unsuitable for high impact technologies such as portable atomic clocks and AR/VR [augmented reality and virtual reality] devices,” explains Mateus Corato Zanarella, a member of Michal Lipson’s nanophotonics group at Columbia. “In our work we show how we can use integrated photonics to drastically shrink the size of complex laser systems.”

Integrated photonics has already revolutionized the way we control light for applications such as data communications, imaging, sensing and biomedical devices, he adds. By routing and shaping light using micro- and nanoscale components, it is now possible to shrink full optical systems down to objects that can fit on a fingertip. Despite great advances, however, high-performance chip-scale lasers have been lacking – meaning that a key component for complete miniaturization remains out of reach.

Columbia’s new on-chip laser platform is the first to demonstrate tuneable and narrow linewidth light at wavelengths shorter than red, with the smallest footprint and shortest wavelength (404 nm) of an integrated laser platform. It is composed of commercial Fabry-Perot laser diodes as the light sources and a photonic integrated chip (PIC) with micron-sized silicon nitride resonators. The latter component is designed to modify the laser emission to be single-frequency, easily tuneable and narrow in linewidth through a physical process known as self-injection locking. Without this PIC, the device would emit at several wavelengths and would not be easily tuneable.

“Each laser diode originally emits impure light of different shades of a colour and we design our PIC to ‘purify’ that emission,” Zanarella tells . “When we combine the diode and the chip, the selective and controllable optical feedback provided by the PIC forces the laser to emit a single colour of high purity instead of multiple shades.”

The researchers say they can generate and control pure light at colours from near-ultraviolet to near-infrared in a precise and fast fashion – up to 267 petahertz/second. Such light could be employed in high-end applications such as portable atomic clocks that were previously not possible because of the of the size of the required laser sources. Other potential applications include quantum information, biosensing, underwater laser ranging (LiDAR) and Li-Fi (visible light communications).

Ultrashort visible light pulses made easy

“What’s exciting about this work is that we’ve used the power of integrated photonics to break the existing paradigm that high-performance visible lasers need to be benchtop and cost tens of thousands of dollars,” Zanarella says. “Until now, it’s been impossible to shrink and mass-deploy technologies that require tuneable and narrow-linewidth visible lasers. A notable example is quantum optics, which demands high-performance lasers of several colours in a single system. We expect that our findings will enable fully integrated visible light systems for existing and new technologies.”

The Columbia researchers now intend to turn their chip-scale laser into standalone units that can be easily deployed in practical applications. They have also filed a patent for their technology, which they describe in .