Long-working-distance grating coupler for integrated optical devices

A novel grating coupler design is presented with its experimental demonstration. The grating can focus the outcoming light upwards without the need of a lens or additional fabrication steps. The lens like effect is introduced by applying a deformation to the grating stripes in order to add a phase map which matches the phase of the spherical wavefront coming from the fiber. The presented grating is designed for silicon photonics technology, and has a working distance of 230 μm to a standard single-mode fiber. This long distance would introduce an excess loss of 9 dB with a standard grating, while with the long-working-distance (LWD) grating we demonstrate no extra loss with respect to the standard grating.