For decades, ultrafast lasers have been some of the most important tools in modern optics and devices. These lasers are capable of producing pulses that last only a few hundred femtoseconds, or in other words, quadrillionths of a second. This has enabled many advances, most notably in eye surgery, precision manufacturing or spectroscopy, the study of light and its movement across objects.
Despite these recent advancements, ultrafast lasers are commonly incredibly expensive and large, occupying an entire optical table’s length of space. These more recent innovations, however, have found a way to dramatically reduce the size of the machinery.
Researchers at Swiss Federal Institute of Technology, led by Professor Tobias J. Kippenberg, have been working day and night to develop this new technology.
Writing in Nature, the researchers first report that the integrated ultrafast laser is capable of achieving performance comparable to conventional tabletop femtosecond lasers while operating completely independently on a photonic chip.
The device is capable of producing pulse energies of 1.05 nanojoules in a duration of a mere 147 femtoseconds, which is a significant step towards making more powerful ultrafast lasers much smaller and also more affordable.
“For more than twenty years, a high-pulse-energy femtosecond laser on chip was widely regarded as a holy grail of integrated photonics,” Kippenberg said. “Our result shows that it is not only possible, but that it can be achieved with a surprisingly elegant architecture that the integrated-photonics community had overlooked.”
The photonic chips use microscopic structures, known as waveguides, in order to control and direct the laser’s light, similarly to how an electronic circuit would guide electricity towards a computer chip.
These waveguides allow for the light to be processed very effectively within these incredibly small structures “etched onto a wafer.” Chips like these are already frequently used within telecommunications, and they have helped researchers shrink the optical technologies that once required the aforementioned larger equipment.
The breakthrough relies on an existing laser design known as a Mamychev oscillator. Although this laser design has been used in other laser systems for various reasons, it has received relatively little attention for integrated photonic systems. This design uses a different kind of waveguide, a nonlinear one, which is positioned between two optical filters which transmit different portions of light across the spectrum, allowing for incredible precision.
As lasers travel through his waveguide, the nonlinear design allows the pulse to spread across a broader range of colors and this broadened light is capable of passing through filters and continue circulating through the laser cavity.
“This design is especially attractive because it does not require any component that is difficult to make on this erbium-doped silicon nitride chip,” Zheru Qiu, a co-leading author of the research, said. This allows for the electronics to be deeply compressed down to a point that the laser only takes up a small space, as opposed to a larger one.
This design could also benefit from large-scale manufacturing. Since designing photonic chips can be produced at the wafer level which is incredibly quick and also cheap, possibly providing ultrafast laser technology to more people.
“With kilowatt-level peak powers, the chip can drive demanding applications that have long depended on large, expensive laboratory lasers,” Qiu said.
Researchers believe the technology could eventually support portable devices for different things like environmental monitoring, material inspections, diagnostics from a medical lens and spectroscopy research. Furthermore, it could contribute to the development of the optical atomic clock, which will be increasingly important in potentially galactic travel and other communications technologies.
