Channel Scalability of Silicon Nitride (De-)multiplexers for Optical Interconnects At 1 m

This paper presents an investigation of the channel scalability of silicon nitride (Si3N4)-based (de-)multiplexers in the 1-mu m band (1015-1055 nm). We discuss 4-, 8- and 16-channel demultiplexers based on arrayed waveguide gratings (AWGs) and cascaded Mach-Zehnder interferometers (MZIs), with corresponding channel spacings of 8, 4 and 2 nm. Gaussian and flat-top response devices are considered for both technologies and we analyze the insertion loss, temperature sensitivity, response flatness, footprint and crosstalk (XT). We study the impact of the number of channels on the insertion loss and XT level. In the experimental part, we demonstrate a 4-channel Gaussian AWG. We also demonstrate 4-channel Gaussian and flat-top cascaded MZIs, based on multimode interferometers (MMIs) and directional couplers (DCs). The AWG is attractive due to its small footprint but its high manufacturing complexity makes the device more prone to fabrication defects, which can lead to higher loss and higher XT. For the Gaussian AWG and MZI, the XT level is approximately the same and increases with the number of channels from -28 to -23 dB at 4 and 16 channels respectively. The flat-top MZI has no extra-loss with respect to the flat-top AWG and has a better tolerance to high temperature operations. However, due to wavelength sensitive DCs, the XT of the flat-top MZI is higher than that of the flat-top AWG except for a 16-channel system.