The development of functional chalcogenide optical phase change materials holds significant promise for advancing optics and photonics applications. Our comprehensive investigation into the solution processing of Sb2Se3 thin films presents a systematic approach from solvent exploration to substrate coating through drop-casting methods and heat treatments. By employing characterization techniques such as scanning electron microscopy, dynamic light scattering, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction, we reveal crucial insights into the structural, compositional, and morphological properties of the films as well as demonstrated techniques for control over these features to ensure requisite optical quality. Our findings, compared with currently reported deposition techniques, highlight the potential of solution deposition as a route for scalable Sb2Se3 film processing.
We present a scalable approach capable of manufacturing high-precision three-dimensional (3-D) GRIN nanocomposites based on multi-component bulk glass-ceramics where we spatially modulate the concentration of high refractive index nanocrystals within a glass matrix. Previously demonstrated in homogeneous thin films and bulk glasses containing large scale liquid-liquid phase separation, this work expands on our efforts to optimize processing protocols employing a near single-phase bulk glass starting material enabling true 3-D modification. Sub-bandgap laser exposure generates Pb-rich amorphous phases within a Ge-As-Pb-Se glass matrix, which undergo crystallization resulting in the formation of highindex nanocrystals upon controlled heat treatment. Nanocrystal density is modulated in both radial and axial geometries by the laser dose, providing spatially tailorable changes in index and dispersion.
Active transition metal ion (TM) doped infrared transparent chalcogenide glasses are a promising class of solid-state materials which can be drawn into a new generation of optical fibers for efficient sources of mid-infrared (MIR) lasers. This work evaluates a candidate glass matrix system of As-S-Se chalcogenide glass as a host for iron (Fe) doped ZnSe crystals. Despite good refractive index match between the chalcogenide glass and the Fe2+:ZnSe particles, the stability of the dopant is critically impacted by the melt temperature conditions. To address this issue, Fe2+:ZnSe particles were coated with a conformal shell of Al2O3, via Atomic Layer Deposition (ALD), to improve the stability of the dopant in the chalcogenide glass matrix melt environment. An ozone pretreatment of the ZnSe powders prior to ALD also improved particle stability, resulting in significant reduction in dissolution of coated powders. Moreover, an improvement in the drying protocol of the glass resulted in significantly lower impurity concentrations. The broadband optical emission of the composites in the 3520-5200 nm region was measured using Er (III):YAG pump laser. Improved ALD coating and drying protocol resulted in a bulk optical composite with higher emission signal compared to previous composite fabricated without these protocols, for the same loading levels.
An etching process is demonstrated for removing noble metal from microstructures to restore their original function after being characterized by scanning electron microscopy (SEM). Using neither aggressive acids nor high temperatures, the etching method gently removes gold/palladium alloys from complex three-dimensional microstructures, preserving their structural form. To explore the efficacy of the etching process, polymeric photonic crystals and monolithic microstructures were fabricated, metal coated, etched, and then structurally and optically characterized. Metal coating substantially diminishes the optical functional and transmission of the microstructures. SEM imaging performed throughout a series of metal sputtering, etching, and resputtering shows that the etching process does not significantly alter the form of a microstructure. Measurements of optical transmission using a scanned-optical-fiber system confirm that the etchant removes the metal and restores the optical properties of the microstructures.
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.
This work reports the fabrication of micron-scale spatially variant photonic crystals (SVPCs) and their use for steering light beams through turns with bending radius Rbend on the order of ten times the optical wavelength λ0. Devices based on conventional photonic crystals, metamaterials, plasmonics and transformation optics have all been explored for controlling light beams and steering them through tight turns. These devices offer promise for photonic interconnects, but they are based on exotic materials, including metals, that make them impractically lossy or difficult to fabricate. Waveguides can also be used to steer light using total internal reflection; however, Rbend of a waveguide must be hundreds of times λ0 to guide light efficiently, which limits their use in optical circuits. SVPCs are spatially variant 3D lattices which can be created in transparent, low-refractive-index media and used to control the propagation of light through the self-collimation effect. SVPCs were fabricated by multi-photon lithography using the commercially available photo-polymer IP-DIP. The SVPCs were structurally and optically characterized and found to be capable of bending light having λ0 = 1.55 μm through a 90-degree turn with Rbend = 10 μm. Curved waveguides with Rbend = 15 μm and 35 μm were also fabricated using IP-DIP and optically characterized. The SVPCs were able to steer the light beams through tighter turns than either waveguide and with higher efficiency.
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