3D Printing Can Now Create Precise and Complex Microlenses

New research demonstrates how 3D printing technology could create highly precise and complex microlenses - miniature reflective surfaces whose diameters are just a few microns.

Microlenses are extremely promising materials that can be used for various optical applications, such as the correction of color distortion during imaging, which would allow for small and lightweight cameras that can be used for different fields.

"The ability to 3D print complex micro-optics means that they can be fabricated directly onto many different surfaces such as the CCD or CMOS chips used in digital cameras," said Michael Schmid, one of the authors of the study from the University of Stuttgart in Germany, in a news release from The Optical Society (OSA). Schmid adds that these microlenses could also be printed directly on the end of optical fibers to create "very small medical endoscopes with excellent imaging quality," describing the tech's potential for medical applications.

Researchers published their findings in the article "3D printed hybrid refractive/diffractive achromat and apochromat for the visible wavelength range," appearing in the OSA journal Optics Letters.

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A New Age for 3D Printing Technologies

To achieve the microlenses with their new 3D printing techniques, researchers built on a technology called two-photon lithography. It uses a focused laser beam to polymerize (solidify) a liquid light-sensitive material known as a photoresist. This lithography method also uses an optical phenomenon, two-photon absorption, which allows very small sections of the photoresist to solidify, which in turn allows the fabrication of complex shapes and structures on the micrometer scale.

The research team behind the latest breakthrough has been studying microlenses and other micro-optics made from two-photon lithography for the past decade. Schmid shares that during their studies, they found color errors called "chromatic aberrations," were present in the images generated with their micro-optics. These findings prompted them to try and develop 3D printed microlenses that would reduce these imaging errors.

To proceed, researchers created smaller versions of conventional lenses used to correct chromatic aberrations, starting with an achromatic lens - a lens that combines refraction and diffraction to limit these aberrations by converging two wavelengths into the same plane. Then, researchers used a commercially available two-photon lithography manufactured by NanoScribe GmbH, a German high-precision manufacturing tool maker. It allowed them to add a diffractive surface to a printed refractive lens in a single step.

Researchers then designed an apochromatic lens, which is generally better at correcting chromatic aberrations compared to achromatic lenses. They did this by combining the refractive-diffractive lens with another lens of different optical characteristics.

Testing the New Microlenses

After creating the new apochromatic lens, they measured the focal spot location for three wavelengths, comparing the results to a simple refractive lens that has no color correction properties. The reference lens that has no correction for chromatic aberrations, displayed focal spots separated by several microns. However, the apochromatic lens from their 3D printing strategy had its focal spots aligned within one micron.

Then, they used the lenses for imaging, with those taken using the reference lens having strong color seams. On the other hand, images taken with the apochromatic lens completely eliminated the color seams.