High-performance MMI devices with low-index contrast structure: analysis and design

Improved approach to low-loss and high-uniformity MMI devices is proposed in this paper. The propagation constant error of guided modes in the MMI region is analyzed. An optimized index contrast is selected to decrease the propagation constant errors of those modes near cutoff. 1 X N MMI splitters designed by this means are analyzed by exact mode analysis. Results show that the loss and uniformity of this new structure are notably improved, especially when N is large. The loss of 0.0892 and uniformity of 0.0826 are acquired when N equals 32.