Research will soon be presented that could bring a new age of photonic communication, with engineers reporting a way to print efficient quantum dot lasers on silicon.

Photonic devices such as quantum dot lasers convert light to electricity for an energy-efficient alternative to traditional copper networks for information transmission.

Unfortunately, such high-end devices have always been expensive.

Recently, research engineers have been trying to bring costs down by building quantum dot lasers directly on silicon substrates. This is because silicon is an extraordinarily common material in the microelectronics industry, and would make it easier and faster for new designs to reach the market.

Now, researchers from the University of California at Santa Barbara (UCSB) say they may have cracked it.

Although quantum dot lasers have been built on silicon before, their performance has not equalled that of quantum dot lasers on substrate platforms made of similar materials as the lasers themselves.

Graduate student Alan Liu and colleagues have demonstrated a new design for quantum dot lasers which not only is grown on silicon but performs as well as similar lasers on their native substrates. 

The team will discuss record-breaking results achieved new such lasers at this year's Optical Fibre Communication Conference and Exposition in San Francisco, hoping their work will be the next step towards large-scale photonic integration in a low-cost form.

Currently, ‘quantum well’ lasers are used for data transmission.

Quantum wells consist of nanometres-thick layers of light-emitting material sandwiched between materials that serve to guide both the electrical current as well as the light output.

A quantum dot laser is similar, but the sheets are replaced with many smaller dots, each a few nanometres high and tens of nanometres across. For perspective, 50 billion of them would fit onto one side of a five cent coin.

“Quantum wells are continuous in two dimensions, so imperfections in one part of the well can affect the entire layer. Quantum dots, however, are independent of each other, and as such they are less sensitive to the crystal imperfections resulting from the growth of laser material on silicon,” Liu said.

“Because of this, we can grow these lasers on larger and cheaper silicon substrates,” he said.

“Because of their small size they require less power to operate than quantum well lasers while outputting more light, so they would enable low-cost silicon photonics.”

The UCSB team has grown quantum dots directly on silicon substrates using a technique known as molecular beam epitaxy, or MBE (epitaxy is the process of growing one crystal on top of another, with the layout of the top layer determined by the one beneath it).

“MBE is the best method for creating high-quality quantum dots that are suitable for use in lasers” because “the entire laser can be grown continuously in a single run, which minimizes potential contamination.”

The MBE approach can also greatly reduce manufacturing costs.

More details are available in the full report, which has been published in the journal Applied Physics Letters. [http://scitation.aip.org/content/aip/journal/apl/104/4/10.1063/1.4863223]