Analysis of long-period waveguide grating arrays

The authors analyze an array of long-period waveguide gratings with coupled-mode theory and show that the grating array can provide effective power transfer among the waveguides at specific wavelengths in the absence of evanescent-field coupling. In particular, they derive the general conditions for obtaining an arbitrary distribution of power splitting ratios among the waveguides and discuss several special cases. They also present a design example using practical waveguide parameters to demonstrate the feasibility of forming such grating arrays for the realization of multiport broadband couplers and add/drop multiplexers.