A High-Performance Optical Amplifier for Microdevices

Researchers at DESY have developed a millimeter-sized high-power amplifier with an output power of more than one watt on silicon-based optical microchips

This output power is a many times higher than what was previously achievable on this tiny scale and enables the use of high-power on-chip amplifiers in the field of integrated photonics instead of external amplifiers. This would make it much easier and cheaper to operate miniaturized devices and sensors, such as those increasingly used in medical surgery, remote sensing by laser, and telecommunications, as well as in optical circuits for future accelerator systems and X-ray sources. The researchers have now confirmed through experiments that these very compact high-performance amplifiers are possible, as they report in the journal Nature Photonics.

High-power amplifiers are critical components in modern optical systems. “In order to be able to use them more widely, such systems should be very small, analogous to microelectronics – preferably in the millimeter range – but without delivering less power. They should also be able to be mass-produced and therefore cost relatively little,” says Neetesh Singh, first author of the study, who works in the DESY group for ultrafast laser and X-ray physics at the Center for Free-Electron Laser Science (CFEL). However, miniaturization has its limits because the smaller an optical system is, the less energy it can store and the less power it can provide. To date, it has not been possible to build suitably small, high-performance optical amplifiers that can be integrated on a microchip. Instead, such microsystems have so far been dependent on external, much larger benchtop amplifiers.

In the new study, however, Singh’s team used a so-called Large Mode Area (LMA) waveguide, which they had previously developed themselves, for the first time to amplify a light signal in a very small space. The critical factor here is the cross-sectional area of the electric field conducted by the waveguide, known as the “mode.” In the current experiments, Singh’s team succeeded in increasing the cross-sectional area of the mode in a photonic waveguide made of silicon nitride and aluminum oxide from just one to 30 square micrometers. This enabled the output power to be increased from a few dozen milliwatts to over one watt … more