Ultrafast optical amplifier

Within optical microchips, light finds its way through channels and waveguides made of silicon. For example, light from a glass fibre is led through a structure of optical channels with splitters and couplers. Silicon is the workhorse for this, but it still only offers passive conduction of light, with some losses as well.

To be able to amplify the signal, or even to include a light source on the chip, extra circuitry has been required. For example, other types of semiconductors, like gallium arsenide, are an option, but materials doped with the rare earth material erbium have shown the additional ability to amplify the light signal.

New technology

Until now, no chip existed which integrated the silicon and erbium-doped material. In her thesis, PhD candidate Laura Agazzi of the University of Twente in the Netherlands demonstrates a working chip for the first time. It will be able to amplify light at data bandwidth speeds up to 170 Gbps. The prototype chip has a signal gain of 7.2 decibel at infrared light 1533 nanometres.

The prototype is really only a starting point, but the results are very promising. One of the  possibilities is a laser with an extremely narrow line width of 1.7 kHz. “In any application that needs emission or amplification of light, this integration of silicon and erbium-doped material is useful. It is not limited to telecommunications. You could use these chips for sensor purposes and for tracing extremely small particles,” Agazzi adds.

Trade-off

Agazzi has investigated the optical properties of aluminium oxide doped with erbium, to understand the mechanisms that influence the amplification properties in a negative way. One of these is called energy-transfer up conversion (ETU), which is detrimental for good functionality. “If you want a large amplification, you would like to put many erbium ions in the material, this in turn can cause a higher ETU. There are possibilities in adapting the host material, causing less interaction of the ions. With my models, I have gained better insight in these and other mechanisms that lower the amplification.

Research

Laura conducted her research within the Integrated Optical Microsystems (IOMS) of Prof Markus Pollnau, which is part of the MESA+ Institute for Nanotechnology of the University of Twente. She has successfully presented and defended her thesis Spectroscopic Excitation and Quenching Processes in Rare-Earth-Ion-Doped Al₂O₃ and their Impact on Amplifier and Laser Performance.