(Nanowerk Highlight) Optical lenses play a vital function in an enormous array of functions, from microscopy and astronomy to images, medical gadgets, and machine imaginative and prescient techniques. Historically, the fabrication of those lenses has relied on a fancy, multi-step course of involving grinding, sharpening, molding, and coating. Every step is important in reaching the specified optical properties and high quality, however the course of is time-consuming, typically requires specialised gear, and might be cost-prohibitive for low-volume, custom-made lenses.
Lately, the emergence of additive manufacturing, or 3D printing, has proven promise as a quicker and cheaper different for producing complicated elements, together with optical elements. Among the many varied 3D printing methods, materials jetting and vat photopolymerization (VPP) have been probably the most extensively used for optical functions because of their excessive precision, quick printing velocity, and the provision of clear supplies. Nonetheless, reaching the optically easy surfaces required for high-quality lenses has remained a problem as a result of inherent limitations of the layer-by-layer printing course of.
The first obstacles have been the presence of stair-stepping defects, which manifest as pixelated steps inside every printed layer (lateral defects) and as layered steps alongside the constructing course (vertical defects). These microscale floor imperfections can considerably degrade optical efficiency. Earlier efforts to mitigate these defects have included utilizing grayscale publicity to blur pixel edges, lowering pixel dimension, and using post-processing methods reminiscent of meniscus coating, grinding, and sharpening. Nonetheless, these strategies have both been restricted of their effectiveness or have launched extra time-consuming steps, undermining the important thing advantages of fast 3D printing.
Now, a group of researchers from Purdue College has developed a custom-made VPP-based lens printing course of that addresses each lateral and vertical stair-stepping defects by integrating two key improvements: unfocused picture projection and precision spin coating. By barely defocusing the curing picture throughout printing, the researchers had been capable of largely get rid of lateral pixelation with out sacrificing construct dimension. They then utilized a fastidiously managed spin coating course of to smoothen the layered steps alongside the constructing course.
The group printed their findings in Superior Useful Supplies (“3D Printing of Optical Lenses Assisted by Precision Spin Coating”).
a) VPP-based 3D printing setup. b) Projection picture for a single printing layer. Mild depth of centered picture c) and unfocused picture d). SEM pictures of printed samples utilizing centered picture e) and unfocused picture f), and after the spin coating course of g). h) 3D printed lens by using the unfocused picture and the precision spin coating. (Picture: Reproduced from DOI:10.1002/adfm.202407165, CC BY)
The precision spin coating course of is a important step on this new approach. Whereas spin coating on curved surfaces was beforehand thought of unpredictable and unrepeatable, the researchers carried out intensive experimental, numerical, and mathematical modeling to exactly management and predict the coating profile. They found that the printed stairs don’t have an effect on the coating profile if the quantity of liquid is ample to cowl the staircases, permitting them to deal with the 3D-printed floor as a easy substrate. Moreover, they discovered that the coating thickness is insensitive to preliminary thicknesses and might be analytically predicted as a perform of time and lens profile. This permits the accuracy of the coating thickness to be managed inside a powerful 1 μm.
Utilizing this progressive strategy, the researchers efficiently demonstrated the precision fabrication of multi-scale spherical, aspherical, and axicon lenses with diameters starting from 3 to 70 mm utilizing high-clarity photocuring resins. The 3D-printed lenses exhibited distinctive floor high quality, with lower than 1 nm floor roughness and 1 μm profile accuracy. Optical characterization revealed that the lenses achieved a most modulation switch perform (MTF) decision of 347.7 lp/mm and demonstrated superior imaging high quality throughout the seen spectrum with minimal distortion.
To additional showcase the flexibility of their approach, the researchers printed varied purposeful optical elements, together with microlens arrays with diameters as small as 0.8 mm, compound parabolic concentrators with a big acceptance angle of 45°, and even an assembled Keplerian laser beam expander with a magnification ratio of 1:2. Additionally they prolonged their methodology to manufacture lenses from different optical supplies, reminiscent of polydimethylsiloxane (PDMS), by 3D printing detrimental molds and utilizing the identical spin coating and post-processing steps.
The importance of this breakthrough lies in its potential to revolutionize lens manufacturing by enabling fast, low-cost, and extremely customizable fabrication of precision optical elements. This know-how may speed up innovation and prototyping in fields reminiscent of customized eyewear, imaginative and prescient correction gadgets, scientific instrumentation, and medical gadgets. By eliminating the necessity for time-consuming and costly conventional lens manufacturing processes, this 3D printing approach may democratize entry to high-quality optical elements and open up new potentialities for freeform optics and superior imaging techniques.
The researchers additionally mentioned a number of areas for future investigation, together with additional optimization of printing parameters for non-axially symmetric lenses, exploration of recent photocurable supplies with tailor-made optical properties, and the potential for spin coating totally different resins with various refractive indices and Abbe numbers to create superior multi-material lenses with enhanced performance, reminiscent of anti-reflection, achromatic correction, or diminished optical loss.
As the sphere of additive manufacturing continues to evolve, the flexibility to quickly produce easy, exact, and customised lenses may turn out to be a robust software for researchers, engineers, and designers throughout a variety of industries. With ongoing refinements and the event of recent supplies, 3D printing has the potential to turn out to be the fourth era of lens making, ushering in a brand new period of optical innovation and customization. This groundbreaking analysis represents a big step ahead in realizing that imaginative and prescient, paving the way in which for quicker, extra accessible, and extra adaptable optics that would remodel a large number of functions.
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