Research of femtosecond laser-assisted etching of fused silica micro-optics devices

Fused silica is widely used in aerospace and precision integrated micro-optical sensors due to its high hardness, low coefficient of thermal expansion, high transmittance properties and high chemical stability in harsh environments. Due to the amorphous characteristics, fused silica wet etching is isotropic and cannot realize specific structural functional devices; dry etching process is complex, costly, and relatively low productivity. These characteristics make the processing of fused silica extremely difficult, with high cost and low yield. Femtosecond laser processing has been widely used in the processing of complex and fine three-dimensional structure of fused silica due to its wide adaptability of materials, high degree of processing fineness and non-mask processing technology, but the surface of the processed surface is relatively rough. Fine micro-optical devices can be realized by wet-assisted femtosecond laser processing. In this study, microstructural patterns were fabricated on fused silica using a tightly focused femtosecond laser by means of a self-developed ultrafast laser processing instrumentation. By controlling the laser processing parameters and the etching time of HF solution to realize the precise modulation of linewidth, period and height of the grating, one/two dimensional gratings, and the Fresnel zone plates with circular and elliptical focal points and the biomimetic compound eye microlens array were successfully fabricated. Finally, the performance of the fabricated optical components were characterized, which were comparable to theoretical simulation values. The results show that the total diffraction efficiency of the fused silica gratings fabricated using this method reaches 85.5%; the Fresnel zone plates and the bionic compound eye microlens array have good focusing effects. This study provides a reference method for the fine micromachining of hard materials such as fused silica, and provides a theoretical basis for its engineering application.