A simple modification of an optical fibre doubles the spectral range of a low-noise supercontinuum source. The advance could improve applications from medical imaging to environmental sensing, where stable broadband light is essential.
Supercontinuum light sources - often called "white lasers" because they emit a massive, continuous rainbow of colors - are essential tools for everything from advanced medical imaging to environmental gas detection. However, researchers have historically faced a frustrating trade-off: a broad spectrum comes at the expense of high fluctuations, which has effectively limited its use.
Now, a research team at DTU Electro has found an elegant way to completely bypass this limitation.
In a newly published study in Optica, the team demonstrated how to double the usable wavelength range of an ultra-low-noise supercontinuum laser. Their system successfully spans from 0.86 to 2.90 micrometers, nearly doubling the spectral range previously achieved by comparable low-noise systems, while maintaining an astonishingly stable noise level.
By combining broad spectral coverage with exceptionally low noise, the new source could improve the speed and sensitivity of technologies that detect weak optical signals, including medical imaging, gas sensing, and spectroscopy. In short, the advance could help clinicians, environmental scientists, and industrial users find faint things faster and more reliably.
"What we have shown is that you can push the spectral width significantly without paying the price in noise, and we do it in just one fiber," explains postdoc and first author Andrea Arduin.
"Noise is what limits sensitivity, and it's the natural enemy of practical applications. If the light fluctuates, it becomes harder to detect weak signals. By keeping the noise low, we make these sources much more useful."
Letting the fibre do the work
The key to the advance is a method the researchers call thermal dispersion engineering.
Normally, different fibre types must be joined together to shape and compress light pulses, which can introduce losses and make systems more complex and less reliable. Instead, the DTU team modified a tiny section of a single optical fibre by heating it.
This heating of a short section of the fibre subtly altered its internal properties, allowing it to reshape the light passing through it. The resulting shorter, more intense pulses generated a much broader spectrum while remaining remarkably stable.
"We essentially let the fibre do the work for us," says Andrea Arduin.
"By carefully shaping its properties, we can boost performance in a very clean and controlled way."
The advance could make a difference in several fields where both precision and speed matter. Such as in medical imaging, where steadier light can produce clearer images and reduce scanning times. In environmental gas sensing, for example, it could allow faster detection of trace amounts of pollutants or greenhouse gases.
"If the light fluctuates, it becomes harder to detect weak signals. By keeping the noise low, we make these sources much more useful."
Because the new source also extends into the infrared, where many molecules exhibit strong spectral signatures, it opens additional possibilities for spectroscopic and sensing applications. Many molecules have distinctive optical signatures in this wavelength range, making it valuable for chemical analysis and the detection of trace gases.
Apart from this, the researchers see the work as a demonstration of a new approach to fibre design. The method offers a broader opportunity: Instead of building increasingly complex optical systems, some functions may be incorporated directly into the fibre itself.
"What I find particularly exciting about our results is that not only did we show record-breaking performance, but we did it with an elegant trick. This pleases the nerd in me, and we are now exploring whether the same approach can be applied to other wavelengths and fibre systems," says Andrea Arduin.