A Two-Channel Silicon Nitride Multimode Interference Coupler with Low Back Reflection

Optical communication systems based on silicon (Si) multimode interference (MMI) wavelength-division multiplexing (WDM) technology can suffer from back reflection. This undesirable characteristic causes losses and is a key problem that can lead to performance limitations. To overcome this limitation, we proposed a new study on how to divide two wavelengths by understanding the light coupling mechanism of the silicon nitride (SiN) MMI coupler over the C-band window and showed four different options to design a two-channel demultiplexer. The best option for a two-channel SiN MMI coupler with low back reflection losses operating in the C-band spectrum was selected. Based on simulation results, the proposed device can transmit two channels with a spacing of 20 nm between wavelengths in the C-band. Moreover, the device has a low power loss range of 0.895-0.936 dB, large bandwidth of 16.96-18.77 nm, and good crosstalk of 23.5-25.86 dB. Usually, a unique design such as angled MMI is required when using Si MMI technology to reduce the back reflection losses. Due to the use of SiN, which has a low refractive index, we obtained a 40.4 dB back-reflection loss without using this angled MMI design. Therefore, this MMI demultiplexer based on SiN can be used in optical communication systems based on the WDM technique to obtain a high data transfer rate in conjunction with low back-reflection losses.

Automated summary

The article discusses the back reflection issue in optical communication systems based on silicon multimode interference technology and proposes a two-channel demultiplexer for the C-band spectrum. Simulation results demonstrate that the proposed device has low power loss, wide bandwidth, and good crosstalk performance. Unlike traditional angled MMI designs, this device utilizes silicon nitride material to achieve lower back-reflection losses without the need for special tilted structures.