Systematic Design of Photonic Crystal Cavities with Ultra-Low Modal Volume Considering Different Fabrication Resolutions

Cavities with a large quality factor to modal volume ratio (Q/V-ratio) facilitate strong light-matter interaction via the Purcell effect [1], which is key for a wide range of photonic and optoelectronic applications, e.g., nonlinear optics [2] and cavity quantum electrodynamics [3]. Previously, many studies have been devoted to designing cavities with enhanced Q/V-ratio by changing locations and radii of air holes in conventional Ln or Hn photonic crystal (PhC) cavities. These cavities increased Q-factors by reducing in-plane loss while keeping diffraction-limited V-values (V − 0.3 (λ/n)³) [4]. Recently, bow-tie shaped PhC cavities consisting of two tip-to-tip components were demonstrated to confine light beyond diffraction limit into a deep sub-wavelength V-value [5]. However the low V-value in these cavities is highly dependent on the feature size and shape, e.g. the width of the bow-tie tip connection. Hence, such cavities are extremely sensitive to manufacturing variations and therefore the attainable fabrication resolution (FR) puts a hard limit on the attainable sub-wavelength V-value in bow-tie shaped PhC cavities. A recent study showed that the bow-tie tip connection could be controlled to 12 nm with an error region of ±5 nm [5].