Improved silica-PLC Mach-Zehnder interferometer type optical switches with error dependence compensation of directional coupler

For the most popular structure of planer lightwave circuit (PLC) 2×2 thermo-optic switches, Mach-Zehnder interferometer (MZI), a full range of splitting ratio errors of directional coupler (DC) are investigated. All the parameters determining the splitting ratio are the dimensions and the refractive indices of the waveguide core and cladding layers. In this work, the coherent relationships between the waveguide size and the refractive indices are analyzed and then the error compensation between the width and the refractive index of waveguide core, and the controllable effect of over clad layer refractive index error upon the MZI-type optical switch are all discovered with numerical calculation and BPM simulations. Then, an MZI-type 2×2 thermo-optic switch having a higher error tolerance is established with the efficient optimizations of all the 3dB-DC parameters. As a result, for the symmetric MZI switch, an insertion loss of 1.5dB and optical extinction ratio of over 20dB are realized for the average tolerance of±5.0%. An asymmetric arm optical phase and unequal arm lengths is also employed to improve the uniformities of insertion loss. The agreements between the designs and the experiments are recognized, leading to a wide adoption of practical silica-PLC optical switch products. •Finds the conditions of 3dB-DC insensitive to the changes of physical parameters.•An asymmetric MZI structure to improve the error tolerance of device performance.•Asymmetric MZI switch verifies the 3dB-DC error tolerance, then mutually optimize.•The agreements among the numerical, BPM software and experimental results.•10% tolerances of WG width/indices make silica-PLC MZI-switch more applicable.