Scientists create powerful lasers that fit on a fingertip

“Our goal is to revolutionize the field of ultrafast photonics by transforming large lab-based systems into chip-sized ones that can be mass produced and field deployed,” said lead researcher Qiushi Guo, a faculty member with the CUNY Advance Science Research Center’s Photonics Initiative and a physics professor at the CUNY Graduate Center. 

Guo clarified that the main aim of his team was to guarantee that these incredibly rapid, chip-sized lasers performed satisfactorily in addition to being smaller. To achieve this, they would need to create devices that could produce sufficient pulse-peak intensity, preferably greater than 1 Watt. 

However, realizing efficient mode-locked lasers small enough to fit on a chip proved a challenging task. To overcome some of the issues inherent in the development of tiny lasers, Guo’s team used thin-film lithium niobate, a well-known crystalline material with unique optical, electro-optic, and piezoelectric properties, to engineer a tiny laser with a high output peak power of 0.5 Watt. 

In addition to being small, the new shrunken mode-locked lasers had numerous interesting qualities that are not present in conventional models. For instance, Guo was able to precisely tune the repetition frequencies of the lasers’ pulses in a very wide range of 200 MHz by varying the lasers’ pump currents. 

Portable and handheld devices

These qualities have significant implications for laser-based applications in the future. With this latest demonstration, Guo's group has cleared a significant barrier toward the realization of scalable, integrated, ultrafast photonic systems that can be implemented in portable and handheld devices. However, further hurdles still need to be addressed and the team said this is just the beginning of their work.

With a goal of achieving pulses of 50 femtoseconds, the researchers intend to keep developing this technology in order to enable it to operate at even shorter timescales and higher peak powers. This would be a 100-fold improvement over the current devices, which produce pulses that are 4.8 picoseconds in length.

“This achievement paves the way for eventually using cell phones to diagnose eye diseases or analyzing food and environments for things like E. coli and dangerous viruses,” Guo said. “It could also enable futuristic chip-scale atomic clocks, which allows navigation when GPS is compromised or unavailable.”

The study is published in the journal Science.

Study abstract:

Mode-locked lasers (MLLs) generate ultrashort pulses with peak powers substantially exceeding their average powers. However, integrated MLLs that drive ultrafast nanophotonic circuits have remained elusive because of their typically low peak powers, lack of controllability, and challenges when integrating with nanophotonic platforms. In this work, we demonstrate an electrically pumped actively MLL in nanophotonic lithium niobate based on its hybrid integration with a III-V semiconductor optical amplifier. Our MLL generates ∼4.8-ps optical pulses around 1065 nm at a repetition rate of ∼10 GHz, with energies exceeding 2.6 pJ and peak powers beyond 0.5 W. The repetition rate and the carrier-envelope offset frequency of the output can be controlled in a wide range by using the driving frequency and the pump current, providing a route for fully stabilized on-chip frequency combs.