Inverse-design of an Ultra-compact and High-efficiency Silicon-on-insulator Mode Expander

We introduce a novel dynamic iterative batch optimization (DIBO) method in combination with the finite-difference time-domain (FDTD) simulation to demonstrate to use of an inverse design method for a segmented mode expander by rapidly varying the waveguide width from 0.45 μm o 10.4 μm (1:23 amplifying ratio). By employing both 2D and 3D FDTD, the DIBO approach enables the achievement of a fundamental transverse-electric (TE) to TE mode conversion within an ultra-small footprint of 19.2×10.4 μm
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on the silicon-on-insulator platform. In the simulation, the mode expander which is optimized to operate at 1550 nm achieves a transmission efficiency of -0.9 dB for TE polarizations as well as a transmission efficiency performance better than -1.137 dB from 1520 to 1580 nm.