A practical multiply resonant photonic crystal nanocavity

Stanford researchers have developed a technique for designing spatially overlapping TE-polarized photonic crystal cavities with broadband tenability which can be fabricated in a thin semiconductor slab. This “cross beam” photonic crystal cavity design consists of crossed 1D nanobeam structures with separately variable lattice constants. This technique can be used in any device incorporating multiple resonances. Compared to previous techniques this approach enables straightforward design and fabrication and allows the use of very thin semiconductor membranes. These structures can serve as polarization independent cavities and are promising for highly efficient on-chip nonlinear frequency conversion. This design also allows the possibility of independent in-coupling and outcoupling via waveguides of very different wavelengths. Stage of Research: 1) Simulated cross beam cavities with bandwidth of up to of 830 nm. 2) Experimentally demonstrated frequency separations of up to 500 nm and Q factors up to 7000. 3) Experimentally demonstrated degenerate two degenerate orthogonally polarized modes at around 1500 nm with Q values of up to 10000. Future work: - Develop a method to separately tune each beam resonance in fabricated structures. - Develop structures for highly efficient on-chip nonlinear frequency conversion.


1) Tunable frequencies of each resonance for a fixed slab size 2) Can use TE modes only which can be strongly localized in thin slabs 3) Can fabricate in thin semiconductor slabs integrate with on-chip semiconductor nanophotonics 4) Can fine tune degenerate frequency resonances to account for fabrication inaccuracies in a straightforward way 5) Can maintain spatial overlap between multiple resonances (e.g. Two separately tunable resonant wavelengths in a single cavity) 6) Modes are individually addressable for input and output coupling 7) Orthogonal modes can be distinguished by polarization or can create a polarization degenerate cavity 8) Resonant recirculation of light at cavity wavelength in ultra-small volume enhances nonlinear frequency conversion efficiency 9) Doubly resonant cavity means higher conversion efficiency in three wave mixing processes due to higher overlap of modes

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