Reconfigurable (pi)-shifted and Mach-Zehnder bandpass filters on the basis of electrooptically induced long-period gratings in a planar waveguide

The concept of a reconfigurable band-stop filter on the basis of an electrically induced long-period grating in a waveguide with an electrooptic core is extended to the design of reconfigurable bandpass filters through introduction of /spl pi/-shift or splitting a grating into two sections that form a Mach-Zehnder (MZ) interferometer. In the proposed design, a single or multiple (pi)-shifts can be easily introduced as well as easily removed in any place along the grating by simply reversing the applied voltage polarity for a portion or portions of the interdigitated electrode (IDE) fingers. On other hand, because coupling does not occur without the presence of the voltage at the finger(s), an MZ interferometer can be easily created, modified, and removed by grounding a number of IDE fingers inside the grating. On the basis of this concept, bandpass transmission characteristics are studied for the gratings with a single (pi)-shift, multiple (pi)-shifts, and MZ interferometers for an arbitrary number of the grounded IDE fingers.