Fig. 3: Design and experimental demonstration of multimode waveguide crossing.

a Illustration of the designed waveguide crossing with an effective size of 15 × 15 μm². b SEM image of the fabricated device. c Simulated electric field profiles for different input modes: TE₀, TE₁ and TE₂. d Microscope image of the cascaded devices connected to auxiliary MUXs for insertion loss measurement. e Measured and fitted insertion losses of TE₀, TE₁, and TE₂ modes at the wavelength of 1550 nm. Black, red and blue lines represent the fitted results of TE₀, TE₁, and TE₂ modes, respectively. f–h Simulated transmission spectra of different mode channels at a wavelength range from 1530 nm to 1570 nm. i–k Measured transmission spectra of different mode channels at a wavelength range from 1530 nm to 1570 nm. Black, red and blue lines represent the detected TE₀, TE₁ and TE₂ modes, respectively, when light is injected into different channels.