Researchers at the City University of New York have demonstrated a new way to create high-performance ultrafast lasers on nanophotonic chips, according to a new cover article published in Science magazine. This miniaturized mode-locked laser can emit a series of ultrashort coherent light pulses at femtosecond (trillionth of a second) intervals.
Ultrafast mode-locked lasers can help unlock the secrets of nature's fastest time scales, such as the formation or breaking of molecular bonds during chemical reactions, or the propagation of light in turbulent media. The high speed, peak pulse intensity, and broad spectral coverage of mode-locked lasers also enable many photonic technologies, including optical atomic clocks, biological imaging, and computers that use light to calculate and process data.
However, the most advanced mode-locked lasers are still extremely expensive desktop systems with high power requirements, which are limited to laboratory use. The goal of the new research is to turn it into a chip-sized system that can be mass-produced and deployed in the field.
Chip-scale ultrafast mode-locked lasers based on nanophotonic lithium niobate. Photo Credit: Alireza Marandi
This time, the researchers used an emerging material platform of thin film lithium niobate (TFLN), which can effectively shape and precisely control laser pulses by applying external radio frequency electrical signals. The team combined the high laser gain of III-V semiconductors with the efficient pulse shaping capability of TFLN nanoscale photonic waveguides to develop a laser emitting 0.5 watts of high peak output power.
In addition to the compact size of a fingertip, the newly demonstrated mode-locked laser also exhibits many characteristics that conventional lasers cannot achieve, such as the ability to precisely tune the repetition rate of output pulses over a wide range of 200 MHz as long as the pump current is adjusted. The team hopes to achieve chip-scale, frequency-stable comb sources through the powerful reconfigurability of lasers, which is essential for precision sensing.
Practical applications of this achievement include the use of mobile phones to diagnose eye diseases, or to analyze E. coli and dangerous viruses in food and the environment, and to navigate when GPS is damaged or unavailable.
