A six-channel angled multimode interferometer in silicon nitride for wavelength division multiplexing

Silicon nitride (SiN) is an ideal material which is compatible with complementary metal-oxide-semiconductor (CMOS) technology. Its advantages include suitability for a large spectral range, low propagation loss and low thermo-optic coefficient, etc. Wavelength division (de)multiplexing (WDM) device is a crucial component for optical transmission networks. In this paper, we demonstrate a six-channel WDM device built with angled multimode interferometer (AMMI) structure in SiN material. Using the first- and second-order self-imaging effects in the multimode waveguides, the number of the multiplexed channels is increased from 3 to 6, without increasing the overall length of the device. The device is designed to operate in the C+L band, and the central wavelength spacing between the neighboring channels is 20nm. The simulation results show that the insertion loss of the device in each channel is less than 0.81dB and the averaged crosstalk of the channels is ~14.9dB. Meanwhile, the device also exhibits low temperature sensitivity and large fabrication tolerance, which is suitable for mass production in commercial foundries.