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(a) A schematic of the optical setup used for the fabrication of 2D and 3D structures. An expanded collimated laser beam passes through the prism, leading to multiple beams to be recombined on the face of a photoresist film-coated substrate. (b) A typical beam geometry, i.e., reciprocal lattice for a 3D fcc-type structure. (c) The specially designed refracting prism with cutting angle . (d) A numerically modeled map of the total exposure across the surface of the photoresist produced by exposing the sample along axis with four beams (50.9° prism). The shaded regions correspond to all points where the exposure dosage is higher than the polymerized threshold and remain insoluble in the developer.
SEM images of PhCs generated by 38.9° prism. (a) 2D hexagonal structures from three side refracted beams. Top-left inset is the first Brillouin zone. (b) and (c) 3D fcc-type structures from four beams with a small magnification view in (b) and a fractured part with (111) in the top and its cleavage plane in (c). A close-up of (111) plane is illustrated in the top left inset of (c). The top right inset in (b) is the typical size of the PhCs we fabricated.
SEM imagies of 3D PhC structures produced with 50.9° prism: (a) The top view of the sample, and (b) the tiled view with top surface (111) and its cross section.
(a) Transmission (dashed line) and reflection (solid line) spectra of 3D periodic structures as shown in Fig. 3. Photonic band gap at around is clearly visible as a pronounced reflection peak and transmission dip. The transmission dip at wavelength stems from polymer absorption bands. The small oscillations in the reflection spectrum are due to the Fabry–Perot interference of the thin polymer film. (b) The corresponding band structure calculation. The gray shaded area corresponds to the measured direction. The dotted lines are guides for the eye. The right-hand side exhibits the reflection spectrum as in (a). Top inset is the first Brillouin zone for this fcc-type PhC structure.
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