Silicon Photonics Foundry Fabricated, Slow-Light Enhanced, Low Power Thermal Phase Shifter
In this research, we developed a low-power silicon photonics foundry-fabricated slow-light thermal phase shifter (SLTPS) where the slow-light (SL) effect is achieved using an integrated Bragg grating (BG) waveguide. Heating the grating induces a red shift in the transmission spectrum, leading to an increased group index $n_g$ during operation, which facilitates a further reduction in the voltage needed for a $π$ phase shift, i.e. $V_π$. Additionally, we investigated a compact Mach-Zehnder Interferometer (MZI) that incorporates the SLTPS in both arms with a phase shifter length of 50 $μ$m. A detailed theoretical analysis was conducted to address the non-idealities of the SL-MZI due to uneven optical power splitting and unbalanced loss in the two MZI arms. The $V_π$ and power consumption for a $π$ phase shift $(P_π)$ of the SL-MZI were quantified for operation in the slow light regime, demonstrating a $V_π$ of 1.1 V and a $P_π$ of 3.63 mW at an operational wavelength near the photonic band edge. The figure of merit (FOM) $P_π \times τ$ is commonly used to assess the performance of thermal optical switches. The SL-MZI in this work has achieved a low $P_π \times τ$ of 5.1 mW $μ$s. Insertion loss of the SL-MZI ranges from 1.3 dB to 4.4 dB depending on the operation wavelength, indicating a trade-off with the $V_π$ reduction.