Researchers propose a new way to connect optical fibers to silicon photonic chips by carving the chip edge in three dimensions. Instead of placing fibers along a single line at the chip facet, their “volumetric edge coupling” idea opens a two‑dimensional region inside the chip edge where light can be coupled. The goal is to let many channels meet many fiber cores without using the chip surface, which is often needed for electronics and metal routing.

The team demonstrated the idea with a single coupling channel in numerical models. Light aimed into an anisotropically etched silicon cavity hits a 54.7° sidewall and undergoes total internal reflection. Even when light is reflected, a small evanescent field extends past the sidewall. A nearby silicon waveguide sitting in that evanescent field can pick up power and guide it into the chip. (Total internal reflection is simply light bouncing inside a denser material, and an evanescent field is the faint “tail” of the light that reaches past the surface.)

To shape how much light is transferred, the designers vary the distance between the reflecting sidewall and the waveguide along the interaction length. They do this by adding a wedged buried oxide (BOX) ridge under the waveguide so the gap changes continuously. That varying gap controls the local coupling strength so the outcoupled light builds a beam that better matches a fiber’s Gaussian mode. The authors note the waveguide in their model is silicon, but the idea could work with other deposited waveguide materials.

The results come from finite‑difference time‑domain (FDTD) simulations. The model predicts a peak coupling efficiency of 88% (−0.56 dB) at 1550 nm and a 1‑dB bandwidth of about 86.45 nm, which covers the telecom C‑band around 1550 nm. The design also shows practical tolerances in the simulations: roughly ±2 µm vertical alignment tolerance, weak sensitivity to lateral offsets up to 5 µm, and a ±0.8° 1‑dB angular tolerance. The reflected field from the sidewall could also be used as an alignment signal to simplify assembly.