a Bilayer photonic crystal (BPhC) consisting of a tunneling layer with a low refractive index sandwiched between two twisted dielectric layers. The 2D photonic crystal is a d = 220-nm-thick crystalline silicon membrane (nSi=3.48) with C6v symmetry-protected triangular shape air holes. The triangular holes have a side length of b=279nm and the unit cell pitch is a=478nm. The interlayer tunneling membrane has a thickness of h=250nm and the refractive index of polymethyl methacrylate (PMMA) is nPMMA=1.48. b Two layers are separated by PMMA with only a subwavelength distance h, suggesting an evanescent coupling between two layers of photonic crystals. c Moiré pattern for a TBPhC, where the two dielectric layers are rotated by angle θ with respect to each other around the AA-stacked center. In a moiré pattern, lattice structure locally resembles the regular stacking arrangement such as AA, AB, and BA. d Evanescent waves from two layers of photonic crystals are mostly coupled in the AA-stacked region
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