Symmetry-selecting gratings and their applications

The basic idea behind a symmetry-selecting grating is to replace a grating written over the entire core cross-section of a waveguide with a grating that is written only over a part of the core. Gratings with a particular symmetry in the horizontal direction can be symmetry-selective, reflecting the modes with that particular symmetry. Here a new type of grating-the fractional core gratings-is proposed and their potential applications to single-, two- and three-wavelength add/drop wavelength filters is discussed and their performance quantified.