Uniform wavelength spacing Mach-Zehnder interferometer using phase-generating couplers

A theoretical and experimental study of an optical interferometer circuit with a uniform wavelength spacing is presented. The operating principle of the filter and a phase-generating coupler (PGC) that can transform a conventional filter into a uniform-wavelength-spaced optical filter is described. As an example, a transformation method is applied to a conventional Mach-Zehnder interferometer (MZI), and the PGC variables are optimized to obtain an MZI with a constant channel spacing of 20 nm. Furthermore, the designed MZI is fabricated using 1.5%-Delta silica-based planar lightwave circuit technology and a 20-nm-spaced MZI is realized with a wavelength displacement that was less than 1.2% of the wavelength period. The fabrication tolerance of the MZI in relation to the PGC design variables is discussed. It is shown that a certain PGC design can increase the fabrication tolerance.