The combination of an analytical approach with a geometrical representation, allows us to derive a rigorous general criterion to design wavelength insensitive interferometers with mirror symmetry, which are needed for wavelength multiplexing/demultiplexing using Bragg grating Mach-Zehnder add/drop filters. Numerical simulations corroborate the analytical results.
Tormen, M., & Cherchi, M. (2005). Design of directional couplers for wavelength flattened Michelson interferometers. In Proceedings of WFOPC2005 - 4th IEEE/LEOS Workshop on Fibres and Optical Passive Components (Vol. 2005, pp. 365–369). https://doi.org/10.1109/WFOPC.2005.1462156