Thermo-optic-enabled topological optimization for tunable ultra-compact silicon photonic device design

Incorporating the thermal dependency of silicon permittivity into topological inverse design methodologies opens the design space for generating novel compact optical devices with temperature actuation for dense photonic integrated circuitry. In this work, a thermo-optic-enabled topological optimization methodology for integrated photonic device design is proposed and experimentally validated through an ultra-compact optical switch. With a footprint of 10 µm by 6~µm, a tenth of the size of conventionally designed MZI-based switches, the device operates in the C-band region with comparable insertion loss (<2 dB) and ON/OFF extinction ratio (<14 dB) performance. At intermediate temperatures, the device operates as a tunable power splitter with an insertion loss below 2 dB over the wavelength range from 1532 to 1555 nm. The tunable splitter achieves various splitting ratios from 0:100 to 100:0 at 1543 nm with a 50:50 splitting ratio that can be maintained over a wavelength range of 23 nm with temperature changes.