Improving chip level laser performance by suppressing noise

For a long time, noise has been the main bottleneck restricting the performance improvement of microchip level Brillouin lasers. Now, researchers in Sydney have successfully overcome this challenge, making significant breakthroughs in the field of integrated photonics and developing an effective noise suppression method. This achievement makes it possible to generate extremely pure and ultra narrowband light sources on compact chips, which will strongly support the development of cutting-edge technologies such as quantum technology, advanced navigation systems, ultra high speed communication networks, and high-precision measurement tools in the future.

The team at the University of Sydney has introduced a way to tame the parasitic processes that emerge inside these lasers as power increases, achieving performance once considered out of reach for chip-scale devices, boldly enabling new photonic possibilities worldwide.

Brillouin lasers are renowned for producing extraordinarily coherent light, making them ideal for applications that require extreme stability and spectral purity. Unlike everyday light sources that emit broad and noisy spectra, Brillouin lasers generate a near-perfect single wavelength capable of supporting optical atomic clocks, quantum sensors and cutting-edge metrology.

However, their potential has been constrained by a phenomenon known as Brillouin cascading. When the laser output is pushed to higher levels, unwanted parasitic modes of light emerge, introducing noise and siphoning energy from the primary mode.

This breakdown in spectral purity poses a serious challenge for real-world technologies that demand consistent, low-noise performance, especially in rapidly evolving quantum and photonic global systems.

The Sydney team tackled this long-standing issue using photonic bandgap engineering, a technique that shapes how light behaves inside microstructures. They precisely inscribed nanoscale Bragg gratings, features more than one hundred times smaller than a human hair, directly into the optical cavity of the laser.

These gratings act as a kind of photonic filter, creating a “dead zone” where parasitic modes cannot form, while leaving the primary mode unimpeded. By modifying the density of optical states inside the cavity, the researchers removed the very conditions that allow cascading to begin.

Without the necessary states to occupy, parasitic modes simply cannot develop, enabling the laser to maintain coherence even at higher and more practical operating power levels safely.

The results demonstrate the effectiveness of this approach. When the Bragg grating was activated, the minimum threshold for Brillouin lasing increased six-fold, preventing cascading from initiating under normal operating conditions.

At the same time, the team measured a 2.5-times increase in the power of the fundamental mode, providing direct evidence that the method boosts usable output while maintaining spectral purity. This combination of higher power and lower noise has been a key goal for photonics researchers working to integrate precision light sources onto chips.

A further innovation lies in the reconfigurability of the Bragg gratings. They can be written, erased and re-tuned after fabrication using only laser light, eliminating the need to manufacture new chips for different operating modes. This programmability means chip-scale lasers can be dynamically configured for single-mode or multi-mode operation, depending on application requirements.

The ability to adjust optical properties post-fabrication represents a major step towards flexible, adaptive photonic systems suitable for a wide range of advanced technologies, supporting future ultra-secure quantum networks.

This breakthrough also offers a general framework for controlling optical interactions on integrated platforms, with implications extending beyond Brillouin lasers. It could lead to cleaner quantum light sources, more stable frequency combs and new device architectures that push photonic chips into regimes previously unattainable.

By giving researchers unprecedented control over the density of states within microresonators, this method opens the door to creating novel classes of light sources essential for quantum computing, precision timing and next-generation communication systems.

The work underscores Australia’s growing leadership in integrated photonics and presents a clear path toward ultra-stable, low-noise and high-power chip-scale lasers capable of supporting the next era of quantum and communication technologies.

Source: opengov