Interferometric sensor method for writing dual fibre Bragg gratings in Mach-Zehnder add/drop multiplexer

Although an all-fibre Mach-Zehnder add/drop multiplexer is an attractive device for telecommunications, various fabrication problems have hindered its widespread realisation. This Letter addresses the problem of fabricating identical fibre Bragg gratings in a Mach-Zehnder add/drop multiplexer. Using the Mach-Zehnder interferometer as a sensor during dual grating fabrication, disparities can be monitored and corrected in real-time and in situ.