Abstract
We theoretically investigate the design of cavities in a three-dimensional (3D) inverse woodpile photonic crystal. This class of cubic diamondlike crystals has a very broad photonic band gap and consists of two perpendicular arrays of pores with a rectangular structure. The point defect that acts as a cavity is centered on the intersection of two intersecting perpendicular pores with a radius that differs from the ones in the bulk of the crystal. We have performed supercell band structure calculations with up to $5\ifmmode\times\else\texttimes\fi{}5\ifmmode\times\else\texttimes\fi{}5$ unit cells. We find that up to five isolated and dispersionless bands appear within the 3D photonic band gap. For each isolated band, the electric-field energy is localized in a volume centered on the point defect, hence the point defect acts as a 3D photonic band gap cavity. The mode volume of the cavities resonances is as small as 0.8 ${\ensuremath{\lambda}}^{3}$ (resonance wavelength cubed), indicating a strong confinement of the light. By varying the radius of the defect pores we found that only donorlike resonances appear for smaller defect radius, whereas no acceptorlike resonances appear for greater defect radius. From a 3D plot of the distribution of the electric-field energy density we conclude that peaks of energy are found in sharp edges situated at the point defect, similar to how electrons collect at such features. This is different from what is observed for cavities in noninverted woodpile structures. Since inverse woodpile crystals can be fabricated from silicon by CMOS-compatible means, we project that single cavities and even cavity arrays can be realized, for wavelength ranges compatible with telecommunication windows in the near infrared.
Highlights
Many efforts are currently proceeding in the blossoming field of nanophotonics to trap light in a tiny volume in space [1,2]
We theoretically investigate the design of cavities in a three-dimensional (3D) inverse woodpile photonic crystal
The electric-field energy is localized in a volume centered on the point defect, the point defect acts as a 3D photonic band gap cavity
Summary
Many efforts are currently proceeding in the blossoming field of nanophotonics to trap light in a tiny volume in space [1,2]. Since a 3D photonic band gap effectively shields an embedded quantum system, such as an excited quantum dot, from vacuum fluctuations, an array of 3D cavities has great potential to control collective quantum systems including qubits [25] It is a major challenge in nanotechnology to realize optical cavities in 3D crystals [26,27], since a controlled deviation from the periodic crystal structure must be realized deep inside the nanostructure. Recent work on silicon inverse woodpile crystals has demonstrated the experimental signature of a broad 3D photonic band gap in reflectivity [46], and a strong inhibition of spontaneous emission of embedded quantum emitters [18]
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