Symmetry-selective reflection gratings.

We show that gratings can be designed to be symmetry selective, that is, reflecting modes with a particular symmetry. The idea behind a symmetry-selective 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. This new kind of grating exhibits high-order reflectivity and selectivity in comparison with standard gratings and enables the design of more effective and compact wavelength add/drop devices.