Theoretical and Experimental Analysis of Dual-Band Grating-Frustrated Coupler

This paper presents results from the theoretical and experimental analysis of add/drop filters based on the grating-frustrated coupler (GFC). GFC filtering heavily relies on synchronous operation, which is difficult to achieve without
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postfabrication processing. The double-GFC (DGFC) is analyzed here in detail as an add/drop filter to reliably achieve synchronism. The DGFC is composed of two gratings to provide a simple method to match the effective indices of the two branches of the coupler. Usefully, the DGFC can also be used as an add/drop filter in two different bands when appropriately designed. Theoretical and experimental results are presented to validate the robustness of the proposed design. The results presented here have been obtained for optical structures working at microwave frequencies to reduce device fabrication complexity while gaining a greater insight into the device operation. However, the concepts discussed in this paper are scalable to the optical domain.