Packaging of silicon photonic devices: Grating structures for high efficiency coupling and a solution for standard integration

Efficient packaging in silicon photonics requires a previous development of high performance fiber coupling structures. One of the most suitable fiber coupling structures in silicon is the grating coupler. Main advantages of using such a vertical coupling technique with respect to horizontal techniques are fiber alignment tolerances and wafer scale testing. We report design, fabrication and experimental measurements of conventional SOI grating couplers. Around 40% coupling efficiency is obtained when coupling a standard singlemode fiber to a singlemode SOI waveguide with 250 nmtimes500 nm section dimensions, with a fiber tilt angle of 10deg. With respect to alignment tolerances, the variation effect of different fiber positions in the grating plane was evaluated as well as different tilt angles. It was obtained that coupling efficiency is almost constant for angle errors of plusmn2deg. In addition, a tolerance of fiber position deviations of about plusmn2 mum was reached, making possible multifiber alignments with the use of standard fiber-arrays. As the obtained vertical orientation is not always easy to adapt to standard layouts, we also introduce here a solution for allowing the use of standard DIL or butterfly packages with horizontal orientation, illustrating the design concepts and briefly describing the technologies involved.