PHASE-SHIFTED BRAGG-GRATING FILTERS WITH IMPROVED TRANSMISSION CHARACTERISTICS

Standard Bragg filters (dielectric waveguides with a grating overlay) show a stopband only in reflection. Filters with quarter-wave-shifted gratings have an extremely narrow transmission peak in the center of t he stopband but its shape (a sharp triangle with a broad bottom) is no t suitable for system design. Using standard coupled-mode theory toget her with transfer-matrix formalism, we show that by introducing severa l phase-shift regions and properly choosing their locations and magnit udes the transmission spectrum can be tailored into a nearly rectangul ar shape. For InP/InGaAsP-based Bragg-grating filters estimates are ma de of achievable channel spacings in wavelength-division multiplexing systems.