Postfabrication optimization of an autoregressive planar waveguide lattice filter

Narrow-band planar waveguide filters are sensitive to fabrication errors that make it difficult to realize multistage filters successfully and maintain tight center wavelength tolerances unless a tuning technique is available. An analysis algorithm combined with waveguide heaters has been successfully used to demonstrate that fabrication errors can be compensated in an autoregressive (AR) lattice architecture that makes it possible to concatenate conveniently multiple stages and to achieve higher-order filter functions. Compensation of fabrication errors on filter functions for a second- and third-order AR lattice filter is presented, and issues related to the application of the analysis algorithm are discussed. In combination with postfabrication tuning of the coupling ratios, the analysis algorithm will allow complete control of the filter function after fabrication.