Fabrication of coherent optical transversal filter consisting of MMI splitter/combiner and thermo-optic amplitude and phase controllers

The fabrication of an integrated-optic coherent transversal filter which is capable of synthesising almost arbitrary filter characteristics is reporte d. The transversal filter consists of a multimode interference (MMI) splitt er for 1 x N signal splitting, delay arms with fixed path length difference , thermo-optic switches and phase shifters for arbitrarily weighting the si gnal and MMI N x 1 combiner to combine N tapped signals. Sine-type and Gaus sian-type spectral filter responses have been successfully realised showing good agreement with theoretical characteristics.