Free-space optical links for board-to-board interconnects

We describe two free-space optical links for multichannel optical interconnects. The targeted aggregate data rate is 240 Gb/s. In one implementation we use a unique implementation of telecentric optics and achieved an optical link that is simple, robust, and modular. We describe a simple, inexpensive telecentric lens that can accommodate all optical channels within a 1-mm-diameter sweet zone. We also describe the performance of an optical link with a 4x4 array of VCSELs and matching detectors. The integrity of the optical link is not significantly degraded with a >+/- 2 mm translational misalignment between the VCSEL and detector arrays. With the telecentric optical link, we need only two low-bandwidth, single-axis active servomechanisms to compensate for static tilt and possibly low-frequency thermally-driven shift between the transmitter and receiver arrays. In the other implementaion we use two matching arrays of 1x12 optical fibers. Data are coupled optically through an air gap of 2 mm by means of a pair of collimating microlens arrays that are aligned to one another via precision mechanical subassemblies. We describe a simple, inexpensive, and robust mechanical coupling for the optical link achieved by using miniature high-flux magnets.