Microresonator boost for chip scale lasers
Researchers in Switzerland have a chip-scale laser source that enhances the performance of semiconductor lasers while enabling the generation of shorter wavelengths.
The team at EPFL’s Photonic Systems Laboratory (PHOSL) integrated semiconductor lasers with silicon nitride photonic circuits containing microresonators. This integration results in a hybrid device capable of emitting highly uniform and precise light in both near-infrared and visible ranges.
The team’s approach involves coupling commercially available semiconductor lasers with a silicon nitride chip created with industry-standard, cost-efficient CMOS technology. The material’s low-loss properties mean there is little to no light that is absorbed or escapes.
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The light from the semiconductor laser flows through microscopic waveguides into extremely small cavities, where the beam is trapped. These micro-ring resonators are intricately designed to resonate at specific frequencies, selectively amplifying the desired wavelengths while attenuating others, thereby achieving enhanced coherence in the emitted light.
The other significant achievement is the hybrid system’s ability to double the frequency of the light coming from the commercial semiconductor laser— enabling a shift from the near-infrared spectrum to the visible light spectrum. While the near infrared spectrum is exploited for telecommunications, higher frequencies are essential for building smaller, more efficient devices where shorter wavelengths are needed, such as in atomic clocks and medical devices.
These shorter wavelengths are achieved when the trapped light in the cavity undergoes a process called all-optical poling, which induces second-order nonlinearity in the silicon nitride. Silicon nitride does not normally incur this specific second order nonlinear effect, and so the system takes advantage of the light’s capacity, when resonating within the cavity, to produce an electromagnetic wave that provokes the nonlinear properties in the material.
“Semiconductor lasers are ubiquitous in modern technology, found in everything from smartphones to fibre optic communications. However, their potential has been limited by a lack of coherence and the inability to generate visible light efficiently,” explains Professor Brès . “Our work not only improves the coherence of these lasers but also shifts their output towards the visible spectrum, opening up new avenues for their use.”
“We are not just improving existing technology but also pushing the boundaries of what’s possible with semiconductor lasers,” says Marco Clementi, who played a key role in the project. “By bridging the gap between telecom and visible wavelengths, we’re opening the door to new applications in fields like biomedical imaging and precision timekeeping.”
doi.org/10.1038/s41377-023-01329-6; www.epfl.ch
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