Fig. 1. (a) Cross-sectional view of the double-layer subwavelength grating mirror, (b) interference of light between the two subwavelength gratings.

Fig. 2. (a) Computed zeroth-order reflectance of the two gratings for TM-polarized light at normal incidence (R12,R23, and Rtotal), (b) round-trip phase of the cavity [δ(λ)].

Fig. 3. Calculated and measured spectra of the double-layer SWG for TM-polarized light.

Fig. 4. SEM top and cross-sectional views of the double-layer SWG on a quartz substrate.

Fig. 5. Fitted and measured spectra of the double-layer SWG for TM-polarized light.