Integrated Photonic Circuits Demonstrate Ultralow Loss

Researchers at École polytechnique fédérale de Lausanne’s (EPFL’s) School of Basic Sciences have developed a technology that produces silicon nitride integrated photonic circuits with low optical losses and small footprints.

Silicon is favored as a material for integrated photonic chips due to its abundance and optical properties, though the material has an optical loss orders of magnitude higher than that of silicon nitride. As a result, silicon nitride has been a material of choice for applications where low loss is critical, such as narrow-linewidth lasers, photonic delay lines, and those in nonlinear photonics.

Integrated silicon nitride photonic chips with meter-long spiral waveguides. Courtesy of Jijun He and Junqiu Liu, EPFL.

In its process, the EPFL team combined nanofabrication and material science, based on the photonic Damascene process developed at EPFL. With this process, the team made integrated circuits of optical losses of only 1 dB/m, a record value for any nonlinear integrated photonic material, according to the researchers.

That low loss considerably reduces the power budget for building chip-scale optical frequency combs, or microcombs, used in applications that include coherent optical transceivers, low-noise microwave synthesizers, lidar, neuromorphic computing, and optical atomic clocks. The team used the new technology to develop meter-long waveguides on 5- × 5-mm² chips and high-quality factor microresonators.

The researchers additionally reported high fabrication yield, essential to scaling up to industrial production.

“These chip devices have already been used for parametric optical amplifiers, narrow-linewidth lasers, and chip-scale frequency combs,” said Junqiu Liu, who led the fabrication at EPFL’s Center of MicroNanoTechnology (CMi). “We are also looking forward to seeing our technology being used for emerging applications such as coherent lidar, photonic neural networks, and quantum computing.”

The research was published in Nature Communications (www.doi.org/10.1038/s41467-021-21973-z).