Scientists Integrate High-performance Laser Mode-locker On Nanophotonic Chip For The First Time

The use of lasers in everyday life has become relatively common, and it can also be an important tool for observing, analyzing, and quantifying things in nature that are invisible to the naked eye - tasks that, unfortunately, have been limited in the past by the need to use large, expensive instruments.
A team of scientists from the City University of New York and the California Institute of Technology team has experimentally demonstrated a new way to fabricate high-performance, ultrafast lasers on nanophotonic chips - they have demonstrated the world's first electrically pumped mode-locked lasers with high peak pulse power integrated on thin-film lithium niobate photo-chips. The research has recently been published as a cover story in the journal Science.
The research is based on miniaturized mode-locked lasers - which emit a unique laser that emits a train of ultrashort pulses of coherent light at femtosecond intervals, according to team leader Qiushi Guo.
Ultrafast mode-locked lasers play a central role in unraveling the mysteries of nature's fastest time scales, which include studying the formation and breaking of molecular bonds in chemical reactions and exploring the dynamics of light propagation in turbulent media.
It is the development of mode-locked lasers, due to their fast pulse peak intensities and broad spectral coverage, that has also fueled the development of a variety of photonics technologies, including optical atomic clocks, bio-imaging, and light-based data computation in computers.
Unfortunately, even today's state-of-the-art mode-locked lasers are still both expensive and power-hungry, which has led to their use being largely limited to laboratory environments.
The goal of the aforementioned team: to revolutionize the field of ultrafast photonics by transforming large laboratory systems into chip-sized systems that can be mass-produced and deployed in the field. They only want to make things smaller, but they also want to make sure that these ultrafast chip-sized lasers provide satisfactory performance. For example, they need sufficient peak pulse intensity, preferably more than 1 watt, to build meaningful chip-scale systems.
However, realizing and integrating efficient mode-locked lasers on a chip is a challenging task. This research uses thin-film lithium niobate (TFLN), an innovative material platform. Using this material, it is possible to precisely control and efficiently form laser pulses by adding an external RF electrical signal.
In their experiments, Guo's team skillfully combined the high laser gain properties of III-V semiconductors with the highly efficient pulse shaping capabilities of TFLN nanophotonic waveguides, ultimately demonstrating a laser with an output peak power of up to 0.5 watts.
In addition to its compact size, the mode-locked laser they demonstrated has a number of exciting new features that can hold great promise for future applications.
For example, by precisely tuning the laser's pump current, Guo realized the ability to fine-tune the output pulse repetition frequency over a wide range of 200 MHz. Using the demonstration laser's robust reconfigurability, the team hopes to facilitate chip-scale, frequency-stabilized comb sources, which are critical for precision sensing applications.
While realizing scalable, integrated, ultrafast photonic systems for portable and handheld devices presents additional challenges for Kuo's team, the current demonstration marks an important milestone in overcoming major hurdles.
This achievement paves the way for using cell phones to diagnose eye diseases or analyze E. coli and dangerous viruses in food and the environment. It could also help create the chip-scale atomic clocks of the future, enabling navigation when GPS is damaged or unavailable.
Scientists have overcome a major hurdle with this latest demonstration. Nonetheless, scientists are now looking forward to tackling the additional hurdles of developing scalable, integrated, ultrafast photonic systems that may be used on portable and handheld devices.