Laser Diffraction Zones and Spots from Three-Dimensional Graded Photonic Super-Crystals and Moiré Photonic Crystals

Abstract

The laser diffraction from periodic structures typically shows isolated and sharp point patterns at zeroth and ±nth orders. Diffraction from 2D graded photonic super-crystals (GPSCs) has demonstrated over 1000 spots due to the fractional diffractions. Here, we report the holographic fabrication of three types of 3D GPSCs through nine beam interferences and their characteristic diffraction patterns. The diffraction spots due to the fractional orders are merged into large-area diffraction zones for these three types of GPSCs. Three distinguishable diffraction patterns have been observed: (a) 3 × 3 Diffraction zones for GPSCs with a weak gradient in unit super-cell, (b) 5 × 5 non-uniform diffraction zones for GPSCs with a strong modulation in long period and a strong gradient in unit super-cell, (c) more than 5 × 5 uniform diffraction zones for GPSCs with a medium gradient in unit super-cell and a medium modulation in long period. The GPSCs with a strong modulation appear as moiré photonic crystals. The diffraction zone pattern not only demonstrates a characterization method for the fabricated 3D GPSCs, but also proves their unique optical properties of the coupling of light from zones with 360° azimuthal angles and broad zenith angles.

Holographic Fabrication of 3D Moiré Photonic Crystals Using Circularly Polarized Laser Beams and a Spatial Light Modulator

“…The diffraction pattern has been used to judge whether the sample is overexposed or not [ 50 ], with a well-developed sample usually showing diffraction zones instead of diffraction spots in the 3D moiré photonic crystal [ 50 ]. Figure 5 a–c shows the diffraction pattern of the 532 nm laser from the 3D moiré photonic crystals in Figure 4 a–c, respectively.…”

“…We initially fabricated 3D moiré photonic crystals through SLM-based holographic lithography using nine-beam interference [ 50 ]. Due to the complex unit super-cells that have been used in the phase pattern, a comprehensive understanding of the relationship between the gray level setting in the SLM and the generated holographic pattern was missing [ 50 ]. Furthermore, many intriguing structures that surpass our imagination have yet to be explored.…”

Light Confinement in Twisted Single-Layer 2D+ Moiré Photonic Crystals and Bilayer Moiré Photonic Crystals

“…The fabrication of a single-layer 2D+ moiré silicon can start from a thick photoresist of SU-8 instead of dipentaerythritol penta-/hexa-acrylate (DPHPA), which is recently used for 3D moiré PhCs [52,53]. The eight-beam interference pattern can be recorded in SU-8, which can be post exposure baked and developed.…”

“…When eight laser beams are separated into two sets with each arranged in different cone angles (where one cone angle is much larger than the other) in holographic interference geometry, twisted moiré PhCs can be fabricated holographically [49][50][51]. By including a central laser beam with eight laser beams in cone arrangement, three-dimensional (3D) moiré PhCs have been fabricated [52,53].…”

The Design of Large Curved Waveguide Based on Sunflower Graded Photonic Crystal

“…The fabrication of 3D photonic crystals has been reported in the relevant literature. For example, Lin et al reported the holographic fabrication of three types of 3D GPSCs through nine beam interferences and their characteristic diffraction patterns [27]. Qi Y et al, according to the structure, selected different exposure thresholds and background materials, and they used the multi-beam interference method to design and experiment to obtain the photon structure with gradient intensity distribution [28].…”