High channel density optical interconnects using photonic crystal fibers

Demanding real-time data processing applications are driving the need for high-throughput programmable logic. Improvements to computing speed from reduction of processor feature sizes are predicted, but these are expected to be hampered within the next 2-5 years by the limitations of metallic interconnects between processors. Optical interconnect alternatives have been attempted, but independent optical channel densities are, at present, restricted by conventional fiber dimensions. In this paper a novel solution to this problem is presented employing a multi-core microstructured fiber. In this type of fiber, a photonic crystal fiber (PCF), the core is a solid silica region surrounded by air holes shot through the length of the fiber. This is created by stacking capillaries and solid canes of silica to create a preform, with the structure preserved after drawing down; a core may be created by replacing an air hole by a solid cane. The criteria for the fiber design are discussed: a bit error rate restriction leads to an upper limit for cross-coupling between cores and hence the distance (or number of air holes) between each channel. Modeling indicates a final fiber design containing 37 cores 31.25 microns apart, equivalent to a density of 1150 independent channels per millimeter squared. Details of an optical transmitting/receiving system utilizing four of the channels and arrays of VCSELs as transmitters and receivers are described. Future improvements to the system are discussed.