Dual-Mode Variable Optical Attenuator Based on Balanced Multimode Power Splitters on SOI Platform

We designed and experimentally demonstrated the dual-mode variable optical attenuator on the silicon-on-insulator platform. The mode-insensitive Mach-Zehnder interferometer structure is achieved by optimizing the initial phase difference, the splitting coefficient of dual-mode splitters, and the thermal modulation efficiency of the phase shifters, ensuring synchronous attenuation of the ${\mathrm {TE}}_{0}$ and ${\mathrm {TE}}_{1}$ modes. At 1550 nm wavelength, experimental results show that the maximum attenuation depths of ${\mathrm {TE}}_{0}$ and ${\mathrm {TE}}_{1}$ modes are 31.33 dB and 20.81 dB, respectively, with driving powers of 23.4 mW and 22.1 mW. Additionally, the measured response time of both modes is under $26~\mu $ s. The device is promising for applications in mode-insensitive optical interconnects.