We present a novel multi-level diffractive optical element for diffractive optic near-field lithography based fabrication of large-area diamond-like photonic crystal structure in a single laser exposure step. A multi-level single-surface phase element was laser fabricated on a thin polymer film by two-photon polymerization. A quarter-period phase shift was designed into the phase elements to generate a 3D periodic intensity distribution of double basis diamond-like structure. Finite difference time domain calculation of near-field diffraction patterns and associated isointensity surfaces are corroborated by definitive demonstration of a diamond-like woodpile structure formed inside thick photoresist. A large number of layers provided a strong stopband in the telecom band that matched predictions of numerical band calculation. SEM and spectral observations indicate good structural uniformity over large exposure area that promises 3D photonic crystal devices with high optical quality for a wide range of motif shapes and symmetries. Optical sensing is demonstrated by spectral shifts of the Gamma-Zeta stopband under liquid emersion.
We demonstrate improved fabrication precision and provide the first spectral characterization of Woodpile-type photonic crystal templates formed by one-dimensional diffractive optical elements. The three-dimensional periodic structures were produced in thick resist by sequential exposures of two orthogonal diffractive optical elements with an argon-ion laser. The observed crystal motif is shown to closely match the iso-intensity surfaces predicted by the interfering diffracted beams. Near-infrared spectroscopic observations reveal the presence of both low and high energy photonic stopbands that correspond with theoretical predictions in several crystal directions. Numerous high-energy stop bands are further reported along very narrow crystallographic angles that attest to the high periodicity and uniformity of the crystal motif through the full resist thickness and over the large sample area. The optical characterization demonstrates the precise control and facile means of diffractive-optical-element based holographic lithography in fabricating large-area three-dimensional photonic crystal templates, defining a promising medium for infiltration with high-refractive-index materials to create photonic bandgap devices.
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