Mach-Zehnder interferometer exactly aligned with ITU grid frequencies

We propose a new Mach-Zehnder interferometer (MZI) that can align passband/rejection-band centers exactly with an arbitrary frequency grid. The proposed MZI incorporates phase-generating couplers, which generate a nonlinear frequency-dependent phase to control the absolute frequency and the dispersion of the waveguide refractive index simultaneously. As an example, we present an MZI that is exactly aligned with the 50-GHz spaced International Telecommunication Union grid. We fabricated the proposed MZI using silica-based planar lightwave circuit technology and demonstrated an MZI with a frequency error of less than ±0.3 GHz over a wide frequency range of 10 THz.