Helical structures with novel optical and mechanical properties have been demonstrated and are commonly used in different fields such as metamaterials, microfluidics and cell scaffold. None of conventional fabrication methods has the throughput or flexibility required for patterning large surface area with tunable pitch. In this paper, we report a novel method for high-throughput volumetric fabricating helical structures with tunable shape based on multiphoton polymerization (MPP) using single-exposure, self-accelerating beam with adjustable rotating intensity profile. The lightfields are generated based on high-order Bessel modes and an analytical model is derived to describe the generation and propagation of light-fields. The method is used to fabricated micro-helices with different pitches and handedness in SU-8 photoresist. Beam splitting and galvo-scanning can be implemented in the system. The fabrication of large-scale helical matrices is demonstrated. Compared to point-by-point scanning, our method increases the fabrication throughput by orders of magnitude, paving the way for adopting MPP for mass production of functional devices in many industrial applications.
We report a computational study of how light propagates within a self-collimating, hexagonal photonic crystal. The photonic crystal can be described as a two-dimensional hexagonal lattice of air holes extruded into the third dimension. While traveling inside the device, light is forced by self-collimation to propagate along the extrusion direction. Finite-difference time-domain calculations show that the lattice must have at least four rings of unit cells surrounding the innermost unit cells where light is centered for it to propagate under strong self-collimation, with low scattering loss.
Helical structures exhibit novel optical and mechanical properties and are commonly used in different fields such as metamaterials and microfluidics. A few methods exist for fabricating helical microstructures, but none of them has the throughput or flexibility required for patterning large surface areas with tunable pitch. In this paper, we report a method for fabricating helical structures with high-throughput and adjustable form based on multiphoton polymerization (MPP) using single-exposure, three-dimensionally structured, self-accelerating, axially tunable light-fields. The light-fields are generated as a superposition of high-order Bessel modes and have a closed-form expression relating the design of the phase mask to the rotation rate of the beam. The method is used to fabricate helices with different pitches and handedness in the material SU-8. Beam splitting and galvo-scanning can be implemented in the system. The fabrication of helical matrices is demonstrated. Compared to point-by-point scanning, our method increases the fabrication speed by two orders of magnitude, paving the way for adopting MPP for mass production of functional devices in many industrial applications.
Multi-photon lithography (MPL) remains among the handful of practical techniques that can be used to fabricate truly three-dimensional (3D) micro- and nanometer-scale structures with few processing steps. Although photopolymers remain the primary material system for MPL, others have been developed for creating functional structures in chalcogenide glasses and polymer-composites. Post-exposure processes have been developed for transforming a structure created by MPL into another material, such as a metal, semiconductor, or oxide glass. MPL has been used to create a wide range of functional nanophotonic devices. The full potential of MPL is apparent in its use to create spatially-variant lattices (SVLs). SVLs are a new class of nanophotonic device that is engineered to direct and control the flow of light in 3D. The devices are based on unit cells that control the propagation of light through the selfcollimation effect. These unit cells are spatially varied in orientation throughout an SVL so that light flows along a prescribed path within the device. The geometry and patterns of the unit cells within the lattice can also be varied to control other key properties, such as phase and polarization. SVLs and their fabrication by MPL opens a new route to 3D integrated photonics, and a myriad of other applications.
Multi-photon lithography (MPL) is a laser-based method for 3D printing nanoscale devices. Since its introduction in the late 1990's, researchers across many disciplines have made exciting contributions toward its development that include extending the range of material systems available for MPL, improving the achievable resolution, and using it to create functional devices for optics, MEMS, microfluidics, sensing, and bio-engineering. MPL has been used to create conventional micro-optics, like waveguides and micro-lenses. It has also been used to fabricate devices onto novel platforms, such as the tips of optical fibers, which greatly extends the functionality of conventional optics and the range of applications they may serve. MPL is unique among existing fabrication methods in its potential for creating truly 3D structures having arbitrary shape and complexity. This is particularly well illustrated in recent reports of using MPL to create spatially-variant photonic crystals (SVPCs). SVPCs unlock new physical mechanisms to control light, particularly using self-collimation to flow beams through exceptionally sharp bends, which cannot be achieved with waveguides and other technologies based on refraction. MPL and SVPCs open new routes to integrated photonics and opto-electronic circuits.
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