High-performance, ultra-fast lasers that fit on a fingertip

Researchers have demonstrated a novel approach for creating high-performance ultra-fast lasers on nanophotonic chips. Qiushi Guo, a physics professor at the CUNY Graduate Center, analysed how to miniaturise mode-lock lasers — a unique laser that emits a train of ultrashort, coherent light pulses in femtosecond intervals, at a quadrillionth of a second.

Ultrafast mode-locked lasers are indispensable for unlocking the secrets of ultrafast timescales in nature, such as the making or breaking of molecular bonds during chemical reactions, or light propagation in a turbulent medium. The high-speed, pulse-peak intensity and broad-spectrum coverage of mode-locked lasers have enabled numerous photonic technologies, including optical atomic clocks, biological imaging, and computers that use light to calculate and process data. However, state-of-the-art mode-locked lasers can be cost-prohibitive and power-demanding tabletop systems that are limited to laboratory use.

Guo’s team of researchers aimed to transform this large lab-based system into a chip-sized alternative that can be mass produced and field deployed. “Not only do we want to make things smaller, but we also want to ensure that these ultrafast chip-sized lasers deliver satisfactory performances. For example, we need enough pulse-peak intensity, preferably over 1 watt, to create meaningful chip-scale systems,” Guo said.

However, realising a mode-locked laser on a chip is not a straightforward process; Guo’s research leverages a material platform known as thin-film lithium niobate (TFLN). This material enables efficient shaping and control of laser pulses by applying an external radio frequency electrical signal. The researchers combined the high laser gain of III-V semiconductors and the efficient pulse-shaping capability of TFLN nanoscale photonic waveguides to demonstrate a laser that can emit a high output peak power of 0.5 W.

The demonstrated mode-locked laser was compact and exhibited many intriguing properties, offering great potential for future applications. For example, by adjusting the pump current of the laser, Guo was able to precisely tune the repetition frequencies of out pulses in a wide range of 200 MHz. By employing the strong reconfigurability of the demonstrated laser, the researchers hope to enable chip-scale, frequency-stabilising comb sources, which are vital for precision sensing. The researchers will need to address additional challenges to realise scalable, integrated, ultrafast photonic systems that can be used in portable and handheld systems.

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

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