All-optical chip-based nanolaser pumping for faster processing

Researchers have developed an all-optical method for driving multiple highly dense nanolaser arrays. The approach could enable chip-based optical communication links that process and move data faster than current electronic-based devices. According to research team leader Myung-Ki Kim from Korea University, the development of optical interconnects equipped with high-density nanolasers could improve information processing in the data centres that move information across the internet. “This could allow streaming of ultra-high-definition movies, enable larger-scale interactive online encounters and games, accelerate the expansion of the Internet of Things and provide the fast connectivity needed for big data analytics,” Kim said.

The researchers demonstrated that densely integrated nanolaser arrays — in which the lasers are just 18 microns apart — can be fully driven and programmed with light from a single optical fibre. Kim said optical devices integrated onto a chip are a promising alternative to electronic integrated devices, which are struggling to keep up with current data processing demands.

“By eliminating the large and complex electrodes typically used to drive laser arrays, we reduced the overall dimensions of the laser array while also eliminating the heat generation and processing delays that come with electrode-based drivers,” Kim said.

The new nanolasers can be used in optical integrated circuit systems, which detect, generate, transmit and process information on a microchip via light. Instead of the fine copper wires used in electronic chips, optical circuits use optical waveguides, which allow higher bandwidths while generating less heat. However, because the size of optical integrated circuits is reaching into the nanometre regime, there is a need for new ways to drive and control their nano-sized light sources efficiently.

To emit light, lasers need to be supplied with energy in a process called pumping. For nanolaser arrays, this is accomplished using a pair of electrodes for each laser within an array, which requires on-chip space and energy consumption while also causing processing delays. To overcome this limitation, the researchers replaced the electrodes with an optical driver that creates programmable patterns of light via interface. This pump light travels through an optical fibre onto which nanolasers are printed.

To demonstrate this approach, the researchers used a high-resolution transfer-printing technique to fabricate multiple photonic crystal nanolasers spaced 18 microns apart. These arrays were applied onto the surface of a 2-micron-diameter optical microfibre, in a way that precisely aligned the nanolaser arrays with the interference pattern. The interference pattern could also be modified by adjusting the driving beam’s polarisation and pulse width.

The research showed that the design allowed multiple nanolaser arrays to be driven using light travelling through a single fibre. The results matched well with numerical calculations and showed that the printed nanolaser arrays could be fully controlled by the pump beam interference patterns.

“Our all-optical laser driving and programming technology can also be applied to chip-based silicon photonics systems, which could play a key role in the development of chip-to-chip or on-chip optical interconnects. However, it would be necessary to prove how independently the modes of a silicon waveguide can be controlled. If this can be done, it would be a huge leap forward in the advancement of on-chip optical interconnects and optical integrated circuits,” Kim said.

The research findings were published in Optica.

Image caption: Researchers have developed a new all-optical method for driving multiple high density nanolaser arrays using light travelling down a single optical fibre. The optical driver creates programmable patterns of light via interference. Image credit: Myung-Ki Kim, Korea University.