Comparison of reflectance spectra of annular cavity array with (a) decreased θ, (b) relationship between resonance dip wavelength and θ, (c) decreased θ′, (d) relationship between resonance dip wavelength and θ′. (e) Cross section of electric field distributions and charge density distributions at a resonance wavelength of 2195 nm. Comparison of reflectance spectra of annular cavity array with (f) increased t, and (g) relationship between resonance dip wavelength and t.