Home / News & events / News / HELIOS results: high efficiency grating coupler

HELIOS results: high efficiency grating coupler

Within the frame of HELIOS, IMEC demonstrated a High-efficiency Silicon-On-Insulator Fiber-to-Chip Grating Couplers Using a Silicon Overlay.

The results have been published as post-deadline paper at Group IV Photonics, San Francisco, USA, 9-11 September 2009

Coupling from a nanophotonic waveguide to the outside world (optical fibers) is not straightforward because of the large mismatch in optical spot size. Grating couplers (figure 1) have been an important innovation for this purpose, allowing to couple light from a chip to a near-vertical optical fiber, on a compact footprint. This is a much more flexible approach than edge coupling, as it is now possible to couple anywhere on a chip, and no postprocessing is needed for coupling, allowing wafer-scale testing prior to packaging.

grating coupler

Test setup

However, most grating couplers demonstrated over the last years have shown coupling efficiencies below 50%m (-3dB), or required complex fabrication techniques. In the framework of the HELIOS project, IMEC demonstrated a new grating coupler design with coupling efficiencies of nearly 70%, using an amorphous or poly-crystalline silicon overlay to create thicker grating teeth (Figure 2). The process can also be integrated with existing waveguide circuits, but requires additional processing steps. For relevant demonstrators, these fiber couplers will be used instead of the traditional couplers, and we aim to improve the coupling efficiency further by optimizing the design parameters (simulations show up to 85% is possible)

Coupling losses