Efficient single-photon routing and switching are crucial for optical quantum computing and communication. For this purpose, all-optical switches are designed for gigahertz bandwidths. The switching mechanism is based on the optical Kerr effect via cross-phase modulation (CPM) of the single-photon signal by a strong 1550-nm pump pulse. For energy-efficient switching, this nonlinear effect is exploited in a microresonator that can either be used directly as an intensity switch in a typical add–drop configuration or as a phase shifter in a Mach–Zehnder interferometer (MZI) structure. To speed up resonance build-up and quenching, a pre-emphasis build and an off-resonance wipe pulse are used. The proposed designs are verified by traveling-wave simulations which demonstrate that 0.1 dB insertion loss and ~1 ns switching windows can be achieved. For a scalable out-of-the-lab transfer, we investigate the feasibility of the proposed switch designs for fabrication in a mature photonic integrated circuit (PIC) platform. In particular, silicon nitride PICs have demonstrated record-low losses which makes them suitable for single-photon applications. By parametric modelling of the microresonator’s directional couplers based on Lumerical EME and 2.5-dimensional varFDTD simulations, the required power transmission coefficients for both signal and pump wavelength can be achieved. This results in an all-optical switch design ready for fabrication in a commercial PIC foundry which can potentially enable scalable architectures for quantum photonic applications.
Establishing a photonic integrated circuit (PIC) process is expensive, and unreachable for most companies. The foundry model (FM), in which a small number of generic foundries (GFs) provide optimized manufacturing facilities to a great mass of fabless circuit designers, lowers the costs and makes PIC technology widely accessible. The downside of GF platforms is the fixed process flow, which limits the design freedom on the physical level. Thus, the PIC performance has to be tweaked and optimized on a circuit level. In this work, we optimize the output power of a laser by circuit level design only. Two methods are investigated experimentally. Firstly, the mirror reflectivity is mapped in order to find an optimum cavity design which maximizes the wall-plug efficiency (WPE). An increased WPE enables a higher output power, since the lower thermal dissipation limits the heating. A WPE around 5 % at a 4.5-mW output power was observed. Secondly, booster semiconductor optical amplifiers (SOAs) can be placed at the laser output, and the saturation power can be increased by tapering the active waveguide. Around 60 mW of output power was achieved for a 500-µm long SOA with a 2-µm to 4-µm linear taper. In conclusion, we have shown that lasers on the considered generic foundry platform can be optimized from a circuit level perspective. Due to the flexibility of the FM, this can potentially benefit a wide range of applications, such as optical communications, sensing, lidars, spectroscopy, and many others.
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