Fabrication of 1 × 8 multimode-interference optical power splitter based on InP using CH₄/H₂ reactive ion etching

1 × 8 multimode-interference (MMI) power splitters with a weakly guided ridge structure based on an InGaAsP/InP material for 1.55 μm operations were designed and fabricated. To determine the optimum etching condition of InP in CH₄/H₂ plasma for the formation of MMI power splitters, the effects of etching parameters, such as flow rates of constituent gases, rf power, and process pressure on the etch rate and surface morphology were investigated. The fabricated 3-μm-wide adjacent straight waveguides have propagation losses of 2.91 dB/cm at 1.55 μm for transverse electric (TE) polarization. The device performances in terms of the thickness of the upper cladding layer were theoretically and experimentally compared. The polarization dependence of the MMI power splitters was investigated. For TE [transverse magnetic (TM)] polarization, the excess loss of the devices at an operating wavelength of 1.55 μm was 1.02 dB (1.95 dB) and the splitting ratio was 0.68 dB (1.13 dB).