(Nanowerk Highlight) Optical lenses play a vital position in an enormous array of purposes, from microscopy and astronomy to images, medical units, and machine imaginative and prescient programs. Historically, the fabrication of those lenses has relied on a posh, multi-step course of involving grinding, sprucing, molding, and coating. Every step is important in attaining the specified optical properties and high quality, however the course of is time-consuming, usually requires specialised tools, and could be cost-prohibitive for low-volume, custom-made lenses.
Lately, the emergence of additive manufacturing, or 3D printing, has proven promise as a sooner and more cost effective various for producing advanced elements, together with optical elements. Among the many numerous 3D printing methods, materials jetting and vat photopolymerization (VPP) have been probably the most broadly used for optical purposes because of their excessive precision, quick printing velocity, and the provision of clear supplies. Nonetheless, attaining the optically easy surfaces required for high-quality lenses has remained a problem because of the 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 similar to meniscus coating, grinding, and sprucing. Nonetheless, these strategies have both been restricted of their effectiveness or have launched further time-consuming steps, undermining the important thing advantages of fast 3D printing.
Now, a staff 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 have been in a position to largely eradicate 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 staff printed their findings in Superior Purposeful 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 targeted picture c) and unfocused picture d). SEM photographs of printed samples utilizing targeted 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 vital step on this new approach. Whereas spin coating on curved surfaces was beforehand thought-about unpredictable and unrepeatable, the researchers carried out in depth 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 enough 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 could be analytically predicted as a perform of time and lens profile. This permits the accuracy of the coating thickness to be managed inside a formidable 1 μm.
Utilizing this revolutionary 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 numerous 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. In addition they prolonged their technique to manufacture lenses from different optical supplies, similar to polydimethylsiloxane (PDMS), by 3D printing destructive 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 similar to customized eyewear, imaginative and prescient correction units, scientific instrumentation, and medical units. 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 programs.
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 latest photocurable supplies with tailor-made optical properties, and the potential for spin coating completely different resins with various refractive indices and Abbe numbers to create superior multi-material lenses with enhanced performance, similar to anti-reflection, achromatic correction, or decreased optical loss.
As the sphere of additive manufacturing continues to evolve, the flexibility to quickly produce easy, exact, and customised lenses may grow to be a robust device for researchers, engineers, and designers throughout a variety of industries. With ongoing refinements and the event of latest supplies, 3D printing has the potential to grow to be the fourth era of lens making, ushering in a brand new period of optical innovation and customization. This groundbreaking analysis represents a major step ahead in realizing that imaginative and prescient, paving the best way for sooner, extra accessible, and extra adaptable optics that might remodel a mess of purposes.
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