Abstract

This paper presents an ultracompact, low-loss, and broadband two-mode division (de)multiplexer. The device structure is based on a two-waveguide asymmetric directional coupler. By maximizing the effective index difference of the even and odd supermodes through proper design of the geometrical parameters of the waveguides, the coupling length without taking the S-bend into account is obtained as 1.4 μm. This is the shortest coupling length, to the best of our knowledge, for transverse-electric modes in mode (de)multiplexers reported until now. In addition to reducing the footprint, this structure improves the mode conversion efficiency while maintaining low-loss and low-crosstalk behavior. The three-dimensional finite-difference-time-domain simulation results show that at the wavelength of 1.55 μm, the mode conversion efficiency, crosstalk, and insertion loss are 99.86%, $-32.7\mathrm{dB}$, and $-0.49\mathrm{dB}$, respectively. Simulation results also demonstrate that the proposed mode (de)multiplexer exhibits low crosstalk of less than $-11\mathrm{dB}$ over a broad bandwidth of 100 nm around the central wavelength of 1.55 μm.

© 2019 Optical Society of America

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