M. Kawasako, T. Watanabe, T. Nagayama, and S. Fukushima "Scalability of Multi-Stage Nested Mach-Zehnder Interferometer Optical Switch with Phase Generating Couplers", Advances in Science, Technology and Engineering Systems Journal, vol. 7, no. 4, pp. 140–146, 2022, doi: 10.25046/aj070418.