Multiwavelength diffraction and apodization using binary superimposed gratings

The binary superimposed grating (BSG), consisting of equal-size segments of two possible values of refractive index and capable of effecting multiwavelength reflection, offers ease of fabrication and great versatility in guided-wave wavelength-division-multiplexing (WDM) applications. We present an analytical formula for the coupling strength of a BSG as a function of segment size, and verify it with numerical transfer matrix simulations of the grating reflectance spectra. Perfect agreement is found for a single grating, and values /spl sim/10%-12% less than predicted for 2-11 superimposed gratings. Subdividing the grating into sections of grouped segments permits step-like apodization, while maintaining binary index and base segment size. Sidemode suppression ratios (SMSRs) of 27 and 16 dB are computed for single-peak and 11-peak BSGs respectively.