In a new study, researchers have shown that 3D printing can be used to manufacture high-precision and complex miniature lenses that are only a few microns in size. Microlenses can be used to correct color distortion during imaging, making it possible to use compact and lightweight cameras for various applications.
According to Michael Schmid, a member of the research team at the University of Stuttgart, Germany, the ability to 3D print complex micro-optical devices means that they can be directly manufactured on many different surfaces, such as CCDs or CCDs used in digital cameras. CMOS chip. Micro-optical devices can also be printed on the end of the optical fiber to create an ultra-small medical endoscope with excellent imaging quality.
In the “Optics Letters” of the Optical Association (OSA), researchers led by Harald Giessen detailed how they used a 3D printing technique called two-photon lithography to produce a combination of refraction And diffractive surface lens. They also showed that combining different materials can improve the optical performance of these lenses.
When testing a new lens, the reference lens (left) showed excellent seams due to chromatic aberration. The 3D printed achromatic lens (middle) greatly reduces these phenomena, while the image taken with the apochromatic lens (right) completely eliminates color distortion.
Researchers used 3D printing technology to create highly accurate and complex apochromatic microlenses that can be used to correct color distortions in the imaging process.
Schmid said that 3D printing of micro-optics has been greatly improved in the past few years and provides design freedom that other methods cannot provide. Our optimization method for 3D printing complex micro-optics opens up many possibilities for creating novel and innovative optical designs that can benefit many research fields and applications.
Break the limits of 3D printing
Two-photon lithography uses a focused laser beam to cure or polymerize a liquid photosensitive material called a photoresist. An optical phenomenon called two-photon absorption polymerizes a cubic micrometer volume of photoresist, which enables the fabrication of complex optical structures on the micrometer scale.
In the past 10 years, the research team has been studying and optimizing micro-optical devices made using two-photon lithography technology. Schmid said that we have noticed that there are chromatic aberrations in some images produced with our micro-optical system, so we set out to design a 3D printed lens with improved optical performance to reduce these errors.
The chromatic aberration occurs because the way light is bent or refracted when it enters the lens depends on the color or wavelength of the light. This means that if no correction is made, the red light will be focused to a different position than the blue light, for example, causing streaks or color gaps in the image.
The researchers designed a miniature lens traditionally used to correct chromatic aberration. They started with an achromatic lens, which combines refractive and diffractive components to limit the effects of chromatic aberration by focusing two wavelengths on the same plane. The researchers used a commercially available two-photon lithography device manufactured by NanoScribe GmbH to add a diffractive surface to the printed smooth refractive lens in one step.
Then, they further designed an apochromatic lens by combining a refractive diffractive lens with another lens made of a different photoresist with different optical properties. The top of the two-material lens with a refractive diffractive surface further reduces chromatic aberration, thereby improving imaging performance. The design was led by Simon Thiele of the Stuttgart Institute of Technical Optics. The company recently established PrintOptics, which provides customers with the entire value chain from design to prototyping to a series of micro-optical systems.
To prove that the new apochromatic lens can reduce chromatic aberration, the researchers measured the focal positions of three wavelengths and compared them with a simple refractive lens without color correction. Although the focal spot of the reference lens without color correction is many microns apart, the focal spot of the apochromatic lens is aligned within 1 micron.
Researchers also use these lenses to obtain images. Images taken with a simple reference mirror show strong color gaps. Although 3D printed achromatic lenses greatly reduce these chromatic aberrations, only images taken with achromatic lenses can completely eliminate color gaps.
Schmid said that our test results show that the performance of 3D printed micro-optical devices can be improved, and two-photon lithography can be used to combine refractive and diffractive surfaces and different photoresists.
The researchers pointed out that the manufacturing time will become faster in the future, which makes this method more practical. Depending on the size, it may currently take several hours to create a micro-optical element. As the technology continues to mature, researchers are working hard to create new lens designs for different applications.
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