Researchers at the University of Twente have successfully developed an ultra-efficient supercontinuous laser on a chip

An ultra-efficient on-chip supercontinuous laser developed by researchers at the University of Twente holds promise for applications ranging from portable medical imaging devices to chemical sensing and lidar. The researchers' design is able to control the dispersion of light in the laser system by alternately widening and narrowing the beam.

Lasers usually emit coherent light, which means that the waves they emit are the same in frequency and waveform. The coherence property of light makes it possible to send narrow beams of light over extremely long distances with very low noise. However, this also means that the laser emission one kinds of color of light, this limits the application.

Supercontinuum lasers produce a continuous color spectrum and can therefore appear white. Until now, generating such a wide color bandwidth required peak power consumption (pulse energy). These lasers tend to be quite large and must be stabilized in the laboratory. They are also quite expensive. For example, although these lasers have been used for 1350D imaging, power efficiency and space consumption limit their application. To reduce the pulse energy required in a CW laser, the researchers used a sign alternating dispersion waveguide. These waveguides are designed to control the scattering of light by alternately widening and narrowing the beam.

In normal dispersive waveguides, frequency generation in supercontinuum generation (SCG) works in tandem with waveguide dispersion to accelerate the time broadening of the pulse, says lead author Haider Zia. Thus, in a normally dispersive SCG, the pulse will rapidly lose peak power, and any further bandwidth generation will stop. In an anomalous dispersive waveguide, dispersion aggregates the resulting frequencies and compresses the pulse in time, thereby increasing its peak power and accelerating bandwidth generation.

However, Zia says, the pulse will eventually form a soliton, where nonlinear production and dispersion work in reverse, so no new spectrum production occurs.

Anomalously dispersive SCGS typically produce greater bandwidth than ordinary dispersive SCGS, but with more spectrum modulation. In both cases, the spectrum broadening stops after a certain length of propagation in the waveguide.

The researchers alternate waveguide dispersion so that when peak power is lost in the normal dispersion segment, the pulse enters the abnormal dispersion segment and regaining peak power. As the pulse begins to mold itself into a soliton, it is destroyed by moving into the next normal dispersion segment.

"Thus, the stasis mechanism in both dispersions is overcome by iterating symbol alternating dispersion," Zia told Photonics Media. "The result is an increase in propagation length, now limited only by propagation losses, in which spectrum can still be generated, thereby reducing the required input power.

This approach also extends bandwidth in the 1 / e (about -4 dB) range, instead of the -30 dB range of traditional SCGS, Zia said. The spectrum power is then more balanced across the bandwidth, which is indispensable for high quality optical devices or pulse compression.

"Our waveguide has a world record 1 / e bandwidth," Zia said. 500 nm, pulse energy starts at 9 pJ, pulse duration is 20 fs, input pulse compression from 200 fs. "They're all focused on the telecommunications wavelength of 1550 nanometers.

The next step for the researchers is to design their waveguide to be integrated with chip-based pulsed laser diodes so that truly integrated wideband wide SCG systems can be developed without the need for small external lasers. Zia says that due to the quality of bandwidth generation as well as the reduced power requirements of waveguides, the technology is already available for portable optical devices that can use SCGS, such as 3D imaging devices.

Source: Laser Net