Ultralow Loss Design Methodology for Energy-Efficient Thermo-Optic Phase Shifters

Thermo-optic phase shifters are crucial components extensively utilized in large-scale photonic integrated circuits due to their simple design and well-established fabrication processes. The requirement for negligible insertion loss in low-power-consumption thermo-optic phase shifters is becoming increasingly critical, particularly in cascaded configurations employed in applications such as LiDAR, photonic computing, programmable photonics, and quantum photonics. To address this need, we present a comprehensive theory based on the fundamental coupled-mode theory for sharp-bent waveguides. We employ phase mismatch in a compact spiral waveguide to eliminate coupling loss and enhance the efficiency of thermo-optic phase shifters. Our approach successfully overcomes inherent trade-offs, demonstrating ultralow insertion loss in compact and power-efficient silicon-based phase shifters operating in the C-band. The proposed simplest-design device exhibits a record lowest measured insertion loss of 0.14 dB among all residual-heat-absorption-type phase shifters. Simultaneously, the power consumption and modulation bandwidth are measured to be 3.4 mW/π and 12.5 kHz, respectively. This methodology holds substantial promise for minimizing the insertion loss across various residual-heat-absorption-type thermo-optic phase shifters, which employ different materials and operate in diverse bands, such as the telecom and visible spectra. The experimental realization of the C-band silicon phase shifter on IMEC’s Si/SiN platform expresses its potential as a fundamental component for scalable mass production in extensive photonic circuit architectures.