Optical waveguide tap with low polarization dependence and flattened wavelength using a Mach–Zehnder directional coupler

The coupling length of a directional coupler is strongly polarization dependent, especially for use in waveguide tap monitoring applications. To avoid severe polarization and maximize the wavelength flatness of optical waveguide taps, a 12 μm thick silicon-on-insulator (SOI) platform and Mach–Zehnder directional couplers implemented with the bending effect illustrated low coupling loss to a SMF-28 fiber, low polarization dependence, and insensitive wavelength on the tap port for monitoring applications. Our results demonstrated that the optical waveguide tap, which carries a portion of the light signal, showed a 0.077 coupling ratio and 0.2 dB for the polarization-dependent loss. The wavelength variation for the coupling ratio was less than 4% across the entire C-band. A 0.26 dB per interface coupling loss was also achieved between the 12 μm thick SOI waveguide and the SMF-28 fiber.