Design of Photonic Crystal Cavities for Extreme Light Concentration

The fields of photonic crystals and plasmonics have taken two different approaches to increasing light−matter interaction. Photonic crystal cavities increase temporal confinement of light in a material, as represented by their high quality factor, while plasmonic structures increase spatial confinement, as represented by their low mode volume. However, the inability to simultaneously attain extreme temporal and spatial confinement of light remains a barrier to realizing ultimate control of light in a material and maximum performance in photonic devices. Here, by engineering the photonic crystal unit cell to incorporate deep subwavelength dielectric inclusions, we show that it is possible in a single structure to achieve a mode volume commensurate with plasmonic elements while maintaining a quality factor that is characteristic of traditional photonic crystal cavities. Manipulating the geometric design of the unit cell leads to precise control of the band structure and mode distribution in the photonic crystal. With a dielectric bow-tie unit cell, photonic crystals can achieve a mode volume as small as 0.0005 (λ/n) with a quality factor as large as 1.75 × 10. Our results demonstrate that there exists a promising alternative to lossy metals for extreme light concentration and manipulation.