Analysis and Design of Low-Loss and Fast All-Optical Switch Elements on Silicon Nitride for Integrated Quantum Photonics

Fast and ultra-low loss single-photon switching and routing are essential for photonic quantum computation and communication. To address this need in a scalable fashion, all-optical switches that can be fabricated in an ultra-low loss and mature Si$_{3}$N$_{4}$ photonic integrated circuit (PIC) foundry platform are designed and optimized for sub-ns switching times suitable for deterministic quantum-dot single-photon sources. The working principle relies on cross-phase modulation (XPM) of the single photons with a 1550-nm pump pulse and is enhanced by a ring resonator. Two different designs of the primary switch element are theoretically studied, namely a ring resonator intensity switch (RRIS) based on resonance shifting due to XPM and a ring resonator phase switch (RRPS) acting as an all-optical phase shifter in a Mach–Zehnder interferometer. As a novel approach to speed up the switching, chirped pre-emphasis and wipe sections for the pump pulses are utilized. A design tool is established from analytical expressions and serves as starting point for further optimization using a dedicated travelling-wave model (TWM). The TWM demonstrates the feasibility of both designs to be driven by either the proposed pre-emphasis pulse shape or a train of chirped Gaussian pulses. While the RRPS turns out to require less pump energy, its operation is more sensitive to pump-power fluctuations. Insertion losses below 0.1 dB and a power consumption below 5 nJ at 1 GHz switching rates for both configurations prove the potential of this concept for scalable quantum photonic applications.