Design and fabrication of a 1×N InGaAsP/InP MMI power splitter with a weakly guided ridge waveguide structure

1×N InGaAsP/InP multimode interference (MMI) power splitters with relaxed fabrication tolerance were fabricated by using a weakly guided ridge structure. We applied the effective index method and the finite difference beam propagation method for device design and simulation. The metalorganic vapor-phase epitaxy grown wafer was processed by conventional photolithography and CH₄/H₂ reactive ion etching for device fabrication. The propagation loss was found to be 2.91 dB/cm at 1.55 μm for the fabricated 3-μm-wide straight waveguides. For TE polarization, the excess losses measured at 1.55 μm were 0.91, 0.83, and 1.02 dB for 1×2, 1×4, and 1×8 MMI power splitters, respectively, and the splitting ratios were below 0.68 dB. Also, the polarization dependence of these devices was investigated. These results show that 1×N power splitters with a weakly guided ridge structure have advantages over a tightly guided ridge structure, i.e., ease in manufacture, which can be used to divide power equally between the N (2, 4 and 8) split output ports with low excess loss, low splitting ratio, low polarization dependence, and acceptable fabrication tolerance.