This paper presents a holographic fabrication of a new type of photonic crystal, called graded photonic super-crystals with graded basis, dual period and dual symmetry. Pixel-by-pixel phase coding of laser beams in a spatial light modulator can produce the highest resolution in produced photonic super-lattice. Two-level designs in phase pattern are used to generate graded photonic super-crystals where graded square lattice clusters are orientated in four, five or six-fold symmetry. Further phase engineering in a super-cell of 12x8 pixels can produce small-period square lattice orientated in a large period rectangular pattern.
Coupling of light to surface plasmons at metal cathode represents a significant light loss in organic light-emitting diode. The newly discovered graded photonic super-crystals with dual periodicity and dual basis, present great opportunity to improve the light out-coupling (The light extraction efficiency) from organic light-emitting diodes. These graded photonic super-crystals can be holographically fabricated by eight beam interference lithography. In this paper, we have computed, through electrodynamic simulation, the light extraction efficiency of planar, organic light-emitting diodes where the Al cathode is patterned with the graded photonic super-crystals. When the cathode of an organic light-emitting device is patterned in the graded photonic super-crystals, a light extraction efficiency up to 70% in the visible range can be achieved.
Transparent conducting oxides are part of a robust material class that is capable of supporting near-IR surface plasmon resonances (SPRs) which are strongly dependent on size, structure, and doping of the material. This study presents the implementation of holographic lithography to structure large area square lattice cylindrical hole arrays on the transparent conducting oxide thin film, aluminum doped zinc oxide (AZO). For fabricated structures on a glass substrate, SPR are indirectly measured by FTIR transmission and verified with electromagnetic simulations using a finite difference time domain method. Furthermore, it is shown that the SPR excited are standing wave resonances in the (1,1) direction of the lattice array located at the interface of the patterned AZO and glass substrate. This research extends the robust CMOS compatible fabrication techniques of holographic lithography into tunable conductive materials,and contributes to the core technology of future integrated photonics.
We report the fabrication of designed defects and regions in photonic crystal templates with differing filling fractions using a spatial light modulator. For the hexagonal lattice, phase patterns with local variance of diffraction efficiency are created using phase tiles from other phase patterns with known diffraction efficiencies. Six-fold symmetric phase patterns are used to generate six beams with locally specified phases. Fourier transform simulations of designed phase patterns are used to guide the filtering process and also give insight into the interference pattern in the 4f plane. Photonic crystal templates are fabricated using exposure of photoresist to the interference patterns generated from the phase patterns with local diffraction efficiency variance displayed on a spatial light modulator. It is shown that local control of filling fraction is achievable using this method. For the square lattice, line defects in polymer lattices are produced using line phase defects in a checkerboard phase pattern. The shifting of the lattice due to the defect phase is investigated. The shifting of lattice around the defects in 2+1 interference is less than that produced by 4+1 interference due to the alternative shifting in lattice in the 2+1 interference. By 45 degree defect orientation and 2+1 interference, the defect orientation can be aligned with the background lattice, the shifting is alternative in lattice, and the shifting is only in one side of the defects, in agreement with the theory prediction.
A method of fabricating large-volume three-dimensional (3D) photonic crystal and quasicrystal templates using holographic lithography is presented. Fabrication is accomplished using a single-beam and single exposure by a reflective optical element (ROE). The ROE is 3D printed support structure which holds reflecting surfaces composed of silicon or gallium arsenide. Large-volume 3D photonic crystal and quasicrystal templates with 4-fold, 5-fold, and 6-fold symmetry were fabricated and found to be in good agreement with simulation. Although the reflective surfaces were setup away from the Brewster's angle, the interference among the reflected s and p-polarizations still generated bicontinuous structures, demonstrating the flexibility of the ROE. The ROE, being a compact and inexpensive alternative to diffractive optical elements and top-cut prisms, facilitates the large-scale integration of holographically fabricated photonic structures into on-chip applications.
Here we present the holographic fabrication of large area 3D photonic structures using a single reflective optical element (ROE) with a single beam, single exposure process. The ROE consists of a 3D printed plastic support that houses 4, 5, or 6-fold symmetrically arranged reflecting surfaces which redirect a central beam into multiple side beams in an umbrella configuration to be used in multi-beam holography. With a circular polarized beam incident to silicon wafer reflecting surfaces at the Brewster angle, multiple linearly s-polarized side beams are generated. 3D photonic crystal structures of woodpile, Penrose quasi-crystal, and hexagonal symmetry were produced with ROEs that have 4+1, 5+1 and 6+1 beam configurations, respectively. Since the ROE design can be readily changed and implemented for different photonic crystal structures, this fabrication method is more versatile and cost effective than currently comparable single optical methods like prisms and phase masks.
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