▎ 摘　　要

This Letter presents an extremely compact graphene-based plasmonic isolator with a two-port multimode interference (MMI) structure. The proposed structure utilizes the non-reciprocal phase shift effect to provide optical isolation. A new approach is used for MMI-based isolator design in terms of mth overall self-imaging. The influence of the device geometries and m parameter on the isolation ratio (ISR), insertion loss, operation bandwidth (BW), and required magnetic field strength B and its appropriate direction is investigated. The device has an ultra-small footprint compared to the operating wavelength of lambda = 8 mu m with high ISR. An MMI isolator with a size of 0.5 mu m x 4.02 mu m (approximate to lambda(2)/32) and ISR = 18.35 dB and an MMI isolator with a size of 0.7 mu m x 7.44 mu m (approximate to lambda(2)/12) with ISR = 27.1 dB are achieved. Moreover, the non-reciprocal MMI shows ultra-wide 20 dB isolation BW of 0.75-2.34 THz. (C) 2020 Optical Society of America