More with less: fault-tolerance and information-theoretic optimality in programmable photonics

To scale up programmable photonic circuits, one must overcome challenges of size, power, and robustness to hardware imperfections. Considering linear multiport interferometers as a concrete example, we show how architectural choices can significantly improve the prospects for scalability. First, we review the field of photonic-circuit error correction, and show how 3-splitter MZI (3-MZI) architectures are more robust to errors than standard MZI architectures, even achieving asymptotic fault-tolerance to hardware imperfections. Second, we discuss the problem of economizing phase-shift, which is especially relevant for power-hungry thermo-optic platforms, and show how the 3-MZI architecture can reduce average phase shifts by a factor of 3-10x in near-term systems.