Demonstrating laser-written waveguides in silicon

Though the use of lasers to write waveguides into dielectric materials is a well-established technique, there have only been a few studies on using this technique on silicon. Motivated by its important applications in microelectronics, Wang et al. demonstrated the writing of waveguides inside silicon wafers.

“With more easily accessible laser sources in the short-wavelength infrared range in recent years, we aim to achieve the same for silicon as what has been done in glass,” said author Shuting Lei.

The researchers focused a pulsed infrared laser inside a silicon sample to write the waveguide and controlled the focal depth by moving the sample toward and away from the source. By translating the sample in the transverse direction and combining this motion with a cylindrical lens beam-shaping technique, they were able to write both straight and circular waveguides of arbitrary length inside the wafers.

They tested the light intensity distributions and loss from light passing through the geometry of both the straight and circular waveguides. They found the quality of both waveguides to be consistent with each other, and identified light scattering due to defects as the main contributor to the waveguide loss.

In order to fully realize the potential of laser-written silicon waveguides, additional work is needed to better characterize the laser-matter interaction mechanisms and the nature of the material modification inside silicon. “A deeper understanding would help us write high quality waveguides inside silicon with minimum loss,” Lei said.

Source: “Nanosecond laser writing of straight and curved waveguides in silicon with shaped beams,” by Xinya Wang, Xiaoming Yu, Matthew Berg, Brett DePaola, Hongyu Shi, Pingping Chen, Lianjie Xue, Xuefeng Chang, and Shuting Lei, Journal of Laser Applications (2020). The article can be accessed at https://doi.org/10.2351/1.5139973 .