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3Multilayer polymer microoptical elements in solid porous silicon dioxide made by two-photon lithography
T. Baluian1'2*, D. Pechkurova1, A. Fedyanin1
1-Lomonosov Moscow State University, Department of Physics. 119991, Russia, Moscow, GSP-1,
Leninskie gory 1
2-MSU-BIT University Shenzhen, Department of Materials Science, Shenzhen 517182, P.R.C.
Modern microoptical devices, especially designed for endoscopic applications and integrated photonics, require high manufacturing accuracy and demand precise alignment. Both of these problems are hard to solve due to small feature size of the optical elements. First problem may be overpassed by applying modern manufacturing techniques, such as two-photon lithography. Two-photon lithography is a precise direct writing method that provides enough accuracy to produce well-shaped microlenses and diffraction elements, for example the microlens was printed directly on the endoscopic fiber in [1]. However, it is still challenging to produce multilayer optics like objectives or multilayer constructions for diffraction neural networks [2] in free space due to structure damage during development. One of the ways to overcome this difficulty is based on using the solid matrix to print elements in. In this work we printed various microoptical elements in the solid matrix of porous silicon dioxide.
Porous silicon dioxide is well-suited for visible light applications due to opacity and low refractive index: it may vary from 1.1 to 1.47 dependent on the pore average size and distribution. We used porous silicon dioxide with average pore size of 40 nm and 80% porosity. The resulting refractive index was 1.14. Pores were filled with OrmoComp photoresist with approximate refractive index 1.51 using the vacuum chamber. After photoresist deposition, we used self-assembled two-photon lithography setup with 780 nm wavelength laser to print various optical elements in the porous silicon dioxide matrix. We also modernised the resist developing technique in order to completely remove non-polymerised photoresist and developer from the nanoscale pores to preserve matrix opacity.
As a result we demonstrate various optical elements printed in the porous silicon dioxide including diffraction grating, set of micro lenses and multilayer masks for visible range diffraction neural networks. It proves that porous silicon dioxide combined with two-photon lithography provides an opportunity to create easy to use compound optical elements that might be integrated with different optical systems.
The work was supported of the Foundation for the Development of Science and Education "Intellect".
[1] T. Gissibl, S. Thiele, A. Herkommer, H. Giessen, Nat. Photon. 2016, 10, 554.
[2] B. Bai, et al, To image, or not to image: class-specific diffractive cameras with all-optical erasure of undesired objects, eLight. - 2022. -Vol. 2. - №. 1. - P. 14.
