Imaging-quality 3D-printed centimeter-scale lens

Significance 

Polymer optics offer incredible versatility that enables development and deployment of sophisticated devices with increasingly complex optics. This can be attributed to their lightweight and compact size properties. These optics are generally made of plastic through injection and molding method that provides numerous options for solution customization to suit desired engineering applications. Due to its unique nature, injection molding generally requires a very disciplined approach for design and fabrication phases.

While injection molding is a well-established fabrication technique for plastic optics, the process faces numerous challenges such as birefringence limitations, high cost and time consumption. To this end, researchers have been working to develop alternative and more efficient options. 3D printing technology has shown great potential for the rapid and cost-efficient production of small-series polymer optics. Indeed, this technique has been demonstrated using various methods including two-photon lithography technology. Unfortunately, the printing of centimeter-scale imaging quality optics has remained difficult due to high surface smoothness and shape requirements.

In a recent paper published in the journal, Optics Express, Dr. Bisrat Assefa, Dr. Henri Partanen, Markku Pekkarinen, Professor Jari Turunen and Professor Jyrki Saarinen from The University of Eastern Finland in collaboration with Joris Biskop at Addoptics investigated the fabrication of imaging-quality optics in macroscopic dimensions using 3D printing technology. Specifically, they demonstrated the workability of an imaging lens with the centimeter-scale diameter whose characteristics are comparable to those of commercial glass lenses.

A typical 3D printing process entails a layer-by-layer inkjet printing technique. Here, a much faster multi-printhead ink-jet printing process based on Luxexcel-Printoptical technology was employed to obtain freeform optics mostly for non-imaging applications. The fabrication approach was iteratively based. This was meant to improve the surface profile accuracy of 3D printed optics by nearly two orders of the magnitude. For convenience and reference purposes, a spherical singlet lens was utilized. Finally, the feasibility of using this 3D printing process for fabricating aspheric optics was evaluated.

The authors successfully fabricated an imaging-quality optics in microscopic dimensions using the 3D printing based Printoptical technology. This method proved better for overcoming the tight tolerances on surface shape and roughness challenges. For instance, the printed singlet lens recorded an excellent surface profile deviation of ±500 nm just within a 12-mm aperture diameter range. On the other hand, RMS surface roughness less than 1nm was reported without post-processing and finishing activities such as surface polishing. The imaging lens exhibited optical performance features similar to those of commercial lenses. In the visible region, for example, an imaging resolution of 140 lp mm-1 at a focal length of 100mm was reported.

Considering the unavailability of polymer materials suitable for an ink-jet process other than the LUX-Opticlear, direct 3D printing of achromatic lens systems is still a challenge. According to the authors, this can be overcome through a combination of 3D printing with silicon molding and vacuum casting techniques or the use of hybrid refractive-diffractive optics. However, the latter have limitations which may lead to the use of alternative techniques.

In summary, Dr. Bisrat Assefa and colleagues study reports the development of new imaging-quality 3D-printed microscopic lens. For the first time, a 3D-printed singlet lens was demonstrated with a relatively excellent surface profile deviation. Additionally, this process proved better for fabrication of freeform optics. Therefore, the study will advance 3D printing technology.

Imaging-quality 3D-printed centimeter-scale lens - Advances in Engineering

About the author

Dr. Bisrat G. Assefa has earned his Ph.D and M.Sc degrees from Institute of Photonics at the University of Eastern Finland (UEF) in the area of Optics and Photonics. He has been working as researcher in the 3D printed photonics and freeform optics research group at UEF from 2014 to 2019 on designing and characterizing 3D-printable optics and photonics elements for imaging, illumination and photonics application.

He was a full scholarship grant winner from UEF while studying his M.Sc degree in Photonics from 2012 to 2014. He also received his B.Sc and M.Sc degrees in Electrical Engineering from Hawassa University and Addis Ababa University in 2009 and 2012, respectively. His expertise broadly lies in the designing, analysis and prototyping of freeform optics, diffractive grating and waveguides.

Reference

Assefa, B., Pekkarinen, M., Partanen, H., Biskop, J., Turunen, J., & Saarinen, J. (2019). Imaging-quality 3D-printed centimeter-scale lens. Optics Express, 27(9), 12630.

Go To Optics Express

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