Twente develops ultra-efficient supercontinuum white light laser on chip

A team of researchers from the University of Twente, Twente, The Netherlands, has made what they are calling "a breakthrough in ultr-aefficient on-chip supercontinuum generation."

The discovery, described in Advanced Photonics Research, represents "a major step forward in the field of integrated photonics and enable applications in portable medical imaging devices, chemical sensing and lidar," they added.

Lasers normally emit light that is coherent: the waves they emit are identical in frequency and waveform. The coherent light makes it possible to send a narrow beam over extreme distances with very low noise.

But this also means that such lasers usually only emit a single wavelength. This limits their applications. In contrast, supercontinuum lasers are able to produce a continuous spectrum of colour and can therefore appear white.

They are used in 3D imaging devices. However, it turns out that to generate this wide bandwidth of colours, supercontinuum lasers have a high peak power consumption (pulse energy), are enormous and have to be stabilized in a laboratory. This makes them expensive and less useful than they could be.

Alternating waveguides

The Twente researchers managed to significantly reduce this pulse energy needed. To do this, the team used so-called sign-alternating-dispersion waveguides. The waveguides are designed to control the dispersion of light by alternately widening and narrowing the beam of light.

"With this method, we reduced the amount of pulse energy needed around a thousandfold compared to traditional methods," commented first-author Haider Zia.

"This is an exciting development in the field of integrated photonics. Our method offers a more efficient way to generate supercontinuum light on a chip, which has many potential applications in medical imaging and lidars."

Paper abstract

The Advanced Photonics Research paper abstract states: "Fully integrated supercontinuum sources on-chip are critical to enabling applications such as portable and mechanically stable medical imaging devices, chemical sensing, and light detection and ranging. However, the low efficiency of current supercontinuum generation schemes prevents full on-chip integration.

"Herein, a scheme where the input energy requirements for integrated supercontinuum generation are drastically lowered by orders of magnitude is presented, for bandwidth generation of the order of 500-1000 nm. Through sign-alternating dispersion in a CMOS-compatible silicon nitride waveguide, an efficiency enhancement by factors reaching 2800 is achieved.

"It is shown that the pulse energy requirement for large-bandwidth supercontinuum generation at high spectral power (e.g., 1/e level) is lowered from nanojoules to 6 picojoules. The lowered pulse energy requirements enable that chip-integrated laser sources, such as mode-locked heterogeneously or hybrid-integrated diode lasers, can be used as a pump source, enabling fully integrated on-chip high-bandwidth supercontinuum sources."