Asymptotically fault-tolerant programmable photonics

Abstract

Component errors limit the scaling of programmable coherent photonic circuits. These errors arise because the standard tunable photonic coupler—the Mach-Zehnder interferometer (MZI)—cannot be perfectly programmed to the cross state. Here, we introduce two modified circuit architectures that overcome this limitation: (1) a 3-splitter MZI mesh for generic errors, and (2) a broadband MZI+Crossing design for correlated errors. Because these designs allow for perfect realization of the cross state, the matrix fidelity no longer degrades with increased mesh size, allowing scaling to arbitrarily large meshes. The proposed architectures support progressive self-configuration, are more compact than previous MZI-doubling schemes, and do not require additional phase shifters. This removes a key limitation to the development of very-large-scale programmable photonic circuits.

Iterative configuration of programmable unitary converter based on few layer redundant multi-plane light conversion

“…2. The maximum of f U (X) 2 is 4N if and only if θ k = ±π for all k, and the minimum is 0 if and only if θ k = 0 for all k. In previous studies, f U (X) 2 has been normalized by N [25], 2N [38], or N 2 [35]. Normalizing by 4N yields 0 ≤ f U (X) 2 /4N ≤ 1, which suggests a good normalization of the norm with a range from 0 to 1 that is independent of N .…”

“…Another approach is the measurement of components with on-chip power monitors, which allows for the calibration of each MZI but also increases the size of the chip and the complexity of wiring [23,24]. Self-configuration and 3-MZI approaches utilize an additional BS to achieve partially perfect linear operation and employ a feedback loop to adjust each phase shift using only output signals [25,26]. While this method allows for infinite scalability, it also increases the size of the circuit and may have issues with stability [27].…”

Multiplexing methods for scaling up photonic logic

“…Recently, we proposed two modified mesh architectures that overcome this limitation: a 3-splitter MZI design that is robust to generic component errors, and a broadband MZI+Crossing design for more realistic correlated errors. 16 Our approach is motivated by the intimate correspondence (Fig. 2(c)) between SU (2) and the Riemann sphere, where a majority of the couplers in a mesh lie near the sphere's north pole (crossing-like state).…”

A Novel Working Scheme for Robust Optical Coupler Unit for Programable Unitary Matrices

“…A common practice for reducing the impact of those errors in as-fabricated POUMs is via algorithm driven closed loop optimization such as nonlinear optimization [9], gradient descent [10], and self-configuration method [11], [12]. Recently, adding an additional beam splitter on the original MZI structure to obtain certain robustness of POUMs against fabrication errors has attracted the interest of researchers [13]. However, the effect of the tuning phase error from the phase modulators on the POUMs has yet to be studied.…”