Apodized surface-corrugated gratings with varying duty cycles

We present the first realization of a Bragg grating apodization based on a concatenation of different duty cycles. The gratings were fabricated in SiON planar waveguides. The reflected signal exhibits a sidelobe suppression better than -20 dB outside a bandwidth of 1.36 nm. At the same time the reflection is stronger than 99.9%, i.e., the resonant light is suppressed better than -30 dB in transmission over 0.22 nm. The gratings are perfectly suited to serve as the wavelength-selective element of a Mach-Zehnder add/drop filter.