Ultracompact Channel Add-Drop Filter Based on Single Multimode Nanobeam Photonic Crystal Cavity

Ultracompact channel add-drop filter utilizing a single nanobeam photonic crystal cavity is analyzed, designed, and demonstrated. Anti-symmetric multimode periodic waveguide structure is employed to implement mode conversion and thus produce degenerate resonant states in the involved nanobeam cavity. Theoretical analysis results indicate that the inter-modal conversion coefficient and the waveguide-cavity coupling coefficient have significant effects on the lineshape of the filter. By carefully engineering the structure of the multimode nanobeam cavity and its side-coupled configuration, we successfully achieve an ultracompact add-drop filter with device area around 20 μm2. The experimental results on silicon-on-insulator (SOI) platform show that the insertion losses of drop port, the crosstalk of add port of the fabricated filter are -1.1 dB and -14.7 dB, respectively. The modal volume of the involved nanobeam cavity are small as 1.2(λ/n)
³
, indicating huge potentials in developing low-power consumption tunable devices for future very large scale integration (VLSI) photonic applications.