Integrated-Optics Multimode-Interference Wavelength Division Multiplexer for Optical Communication

An integrated-optics multimode-interference 1.3 1.55-mum wavelength division mul tiplexer demultiplexer for optical communication is reported. We have found that the device length can be reduced by adopting a restricted-resonance multimode-interference scheme and a lower beat length ratio. The former allows the device length to be 3 times shorter, and the latter has been found to be able to avoid the wavelength insensitivity of the multimode-interference effects. Modal propagation analysis was used to investigate transmission characteristics of the device. Simulation results show that a demultiplexer with contrasts of 40 dB at 1.3-mum wavelength and 34.5 dB at 1.55 mum can be achieved at an optimum coupler length of 435.5 mum. We have also discussed the fabrication and operation tolerances of the wavelength multiplexer and the effect of the wavelength-dependent refractive index.