Determination of the optimum cluster parameters for a clustered free-space optical interconnect

Parallel free-space parallel optical interconnects (FSOIs) have great potential for use as high bandwidth interconnects at the board-to-board and chip-to-chip levels Recent reports of the integration of large (1024) arrays of vertical-cavity surface-emitting laser (VCSEL) arrays to complementary metal-oxide semiconductor (CMOS) suggest that large parallel interconnects should be possible in this technology. We have introduced a technique to determine the optimum cluster dimensions for a free-space optical interconnect which deliver the maximum channel density for a given degree of misalignment tolerance. The sources are assumed to be multimode VCSELs (wavelength 850 nm, mode field diameter 6 μm, M2 factor of 1.93 and VCSEL pitch 125 μm). They are collimated by microlenses with a focal length of 250 μm. The required interconnection distance results in a minilens focal length of 8.5 mm (assuming a single relay block to route the optical channels). This technique will be extended to cover arbitrary focal lengths and source parameters by incorporating an analytical calculation of ray aberrations. This approach has the potential to considerably simplify the design of clustered free-space optical interconnects.