Mode-Group (De)Multiplexer Based on Directional Coupler Formed by Heterogeneous Integrated Waveguides

A simple mode-group (de)multiplexer utilizing a co-planar directional coupler formed by heterogeneous waveguides is proposed, which features two few-mode cores with different refractive indices and heights. The proposed device enables the control of mode-group (de)multiplexing between two few-mode cores, i.e., for manipulating both the E21 and E12 modes as a mode group. A three-mode (de)multiplexer is designed and fabricated with polymer materials through multi-step photolithography to demonstrate the proposed methodology, where only the high-order modes couple between two few-mode cores. For E21 mode and E12 mode, a coupling ratio higher than 90.6% and 89.9% is measured of our device within the C-band, ranging from 1530 to 1565 nm. A low polarization state sensitivity is confirmed by modal crosstalk lower than −9.8 dB and −9.5 dB to the E11 mode from E21 mode and E12 mode, respectively. A modal crosstalk lower than −17.8 dB to both the E21 and E12 modes from E11 mode is represented. The proposed mode-group (de)multiplexer can be further developed to manipulate more guide mode groups, and the crosstalks can be further decreased by introducing horizontal and vertical tapers during the fabrication. The device proposed can find application in photonic integrated chips where mode-group manipulations are required. Received: 23 June 2024 | Revised: 14 August 2024 | Accepted: 5 December 2024 Conflicts of Interest Quandong Huang is a Peer Review Support Specialist for Journal of Optics and Photonics Research and was not involved in the editorial review or the decision to publish this article. The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data are available from the corresponding author upon reasonable request. Author Contribution Statement Jiali Zhang: Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Kedi Peng: Software, Writing – review & editing, Visualization. Jiaqi Ran: Writing – review & editing. Yaomin Wu: Writing – review & editing. Jiadong Xiao: Writing – review & editing. Yujian Chen: Writing – review & editing. Yarou Chen: Writing – review & editing. Ou Xu: Validation, Supervision. Quandong Huang: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration, Funding acquisition.