Mitigating Phase Error Accumulation in Programming MZI-Based Optical Processors

The practical implementation of reconfigurable interferometric-based optical processors requires complicated and time-consuming calibration and programming schemes to address errors induced by fabrication process variations. Among the various prevalent mesh topologies, the presence of a diagonal path inherently provides independent access to calibrate, monitor, and program each phase shifter, regardless of any existing dynamic errors in the bias of other blocks. In other words, the phase error of MZIs do not accumulate along a diagonal path. This attribute of the diagonal path has been experimentally validated in a 4×4 Bokun mesh topology by introducing phase distortion in the previous Mach-Zehnder interferometer block along the same diagonal path. Measurements demonstrate that the same phase distortion in a mesh topology lacking this attribute can lead to accumulating calibration and programming errors. The Bokun mesh topology, with its inherent beneficial attributes, supports the realization of significantly superior performance in the case of on-chip weight optimization, referred to as in-situ programming, due to enabling an error-free, faster, and easier programming scheme.