KEYWORDS: Microspheres, Optical lithography, Light sources and illumination, Spatial light modulators, Process control, Liquid crystals, Digital micromirror devices, Digital Light Processing, Control systems, Resonators
Microsphere photolithography (MPL) uses self-assembled hexagonal close-packed microspheres as optical elements to produce photonic nanojets (PNJ) in a layer of photoresist. The information required for hierarchical patterning is embedded in the illumination light field. In this work, dual spatial light modulator (SLM) system is employed to attain precise control over the light field in MPL, which can significantly enhance the flexibility and efficiency of the fabrication process. A digital micro device (DMD) located at the front Fourier plane is used to control the AOI at the back focal plane. A liquid crystal (LC) device is placed in the intermediate image plane to regulate the local illumination intensity, which is subsequently projected onto the image stage. Both the DMD and SLM encode the illumination AOI and intensity received by each microsphere. The resolution and control processes of the system are investigated. The capability is demonstrated by creating functional hierarchical metasurfaces.
We investigate the digital glass forming process for depositing commercial SMF-28 single-mode optical fiber for photonic purposes. The process utilizes a CO2 laser to locally heat the feedstock to fuse it onto a fused quartz substrate. We focus on how altering the deposition parameters, including the laser power, feed rate, and path plan, affects the deposited fiber morphology and how this affects the optical transmission. At high powers, the fiber bonds strongly to the substrate, resulting in significant changes in fiber morphology and core shape. With a gradient transition between the feedstock geometry and the deposition geometry, high optical transmission for straight line depositions can be achieved. Additional work was performed examining the optical losses when the fiber is deposited around a constant radius curve for different fiber morphologies, with higher losses recorded for higher power samples. Comparing the doping profile of these samples indicates that the gradient of Ge decreases at higher laser power, suggesting the losses are caused by diffusion of the fiber core. This work shows that for high input powers, the optical losses around curves are increased, leading to a tradeoff between the bonding strength and optical transmission for these geometries.
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