Ultra-Broadband and Multi-Channel Polarization- Insensitive Multimode Waveguide Crossings

As an important building block in on-chip multi-dimensional division multiplexing photonic circuits allowing the complex network routing, an ultra-broadband and polarization- insensitive 3×3 multimode waveguide crossing is demonstrated herein. The dual-step etched waveguide scheme combined with particle swarm optimization can constrain the light diffraction for different physical dimensions (wavelength, mode, and polarization) in the cross region, thereby achieving high-performance and multi-functional characteristics. Simulations show that our proposed multimode waveguide crossing has low insertion losses (< 0.23 dB) and low crosstalks (< -22 dB) for the four modes (TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>, TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub>, TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>, and TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub>) over the 350 nm wavelength range (1250-1600 nm). The calculated results also indicate that the device has good fabrication tolerance. For the fabricated device, the measured losses are less than 0.47 and 0.51 dB and crosstalks are lower than -22 and -21 dB in two operating bands (1285-1335 nm and 1520-1580 nm). This work shows great potential for large-scale and high-density integration of on-chip multi-dimensional optical interconnect and communication systems.