title: Robust polarization-insensitive strip-slot waveguide mode converter based on symmetric multimode interference.
abstract: Strip-slot waveguide mode converters for TE0have been widely investigated. Here we demonstrate a polarization-insensitive converter numerically and experimentally. The polarization-insensitive performance is achieved by matching the optical field distribution of the 2-fold image of the Multimode Interference (MMI) and the TE0(TM0) mode of a slot waveguide. The working principle for this MMI-based mode converter is thoroughly analyzed with the quantitatively evaluated optical field overlap ratio that is theoretically derived from the orthonormal relation of eigenmodes. Based on the analysis, the MMI-based polarization-insensitive converters are then simulated and fabricated. The simulation and measurement results indicate that the proposed scheme is a robust design since it is not only polarization-insensitive but also wavelength-insensitive and fabrication-tolerant. Moreover, the mode converter is as small as 1.22 μm × 4 μm while the measured conversion efficiencies are 95.9% for TE0and 96.6% for TM0. All these excellent properties make the proposed mode converter an ideal solution for coupling light between strip and slot waveguides when both TE and TM polarizations are considered.
authors.forename: Qingzhong
authors.initials: Q
authors.lastname: Deng
authors.forename: Qiaojing
authors.initials: Q
authors.lastname: Yan
authors.forename: Lu
authors.initials: L
authors.lastname: Liu
authors.forename: Xinbai
authors.initials: X
authors.lastname: Li
authors.forename: Jurgen
authors.initials: J
authors.lastname: Michel
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Zhou