Process technology enables ultra-low-loss integrated photonic circuits

April 20, 2021 // By Jean-Pierre Joosting
Process technology enables ultralow-loss integrated photonic circuits
Combining nanofabrication and material science, this photonic process technology has enabled integrated photonic circuits with optical losses of only 1 dB/m, a record value

A group of scientists led by Professor Tobias J. Kippenberg at the EPFL School of Basic Sciences has developed a new technology for building silicon nitride integrated photonic circuits with record low optical losses and small footprints.

Integrated photonic chips are usually made from silicon that is abundant and has good optical properties. But silicon can't do everything we need in integrated photonics, so new material platforms have emerged. One of these is silicon nitride (Si3N4), whose exceptionally low optical loss (orders of magnitude lower than that of silicon), has made it the material of choice for applications for which low loss is critical, such as narrow-linewidth lasers, photonic delay lines, and nonlinear photonics.

Combining nanofabrication and material science, the technology is based on the photonic Damascene process developed at Ecole Polytechnique Fédérale de Lausanne (EPFL). Using this process, the team made integrated circuits of optical losses of only 1 dB/m, a record value for any nonlinear integrated photonic material. Such low loss significantly reduces the power budget for building chip-scale optical frequency combs ("microcombs"), used in applications like coherent optical transceivers, low-noise microwave synthesizers, LiDAR, neuromorphic computing, and even optical atomic clocks. The team used the new technology to develop meter-long waveguides on 5x5 mm2 chips and high-quality-factor microresonators. They also report high fabrication yield, which is essential for scaling up to industrial production.

Picture: 
Integrated silicon nitride photonic chips with meter-long spiral waveguides. Image courtesy of Jijun He, Junqiu Liu (EPFL).

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