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Natural compound eyes provide the inspiration for developing artificial optical devices that feature a large field of view (FOV). However, the imaging ability of artificial compound eyes is generally based on the large number of ommatidia. The lack of a tunable imaging mechanism significantly limits the practical applications of artificial compound eyes, for instance, distinguishing targets at different distances. Herein, we reported zoom compound eyes that enable variable-focus imaging by integrating a deformable poly­(dimethylsiloxane) (PDMS) microlens array (MLA) with a microfluidic chamber. The thin and soft PDMS MLA was fabricated by soft lithography using a hard template prepared by a combined technology of femtosecond laser processing and wet etching. As compared with other mechanical machining strategies, our combined technology features high flexibility, efficiency, and uniformity, as well as designable processing capability, since the size, distribution, and arrangement of the ommatidia can be well controlled during femtosecond laser processing. By tuning the volume of water injected into the chamber, the PDMS MLA can deform from a planar structure to a hemispherical shape, evolving into a tunable compound eye of variable FOV up to 180°. More importantly, the tunable chamber can functionalize as the main zoom lens for tunable imaging, which endows the compound eye with the additional capability of distinguishing targets at different distances. Its focal length can be turned from 3.03 mm to infinity with an angular resolution of 3.86 × 10–4 rad. This zoom compound eye combines the advantages of monocular eyes and compound eyes together, holding great promise for developing advanced micro-optical devices that enable large FOV and variable-focus imaging.

We report fabrication of silica convex microlens arrays with controlled shape, size, and curvature by femtosecond laser direct writing. A backside etching in dye solution was utilized for laser machining high-fidelity control of material removal and real-time surface cleaning from ablation debris. Thermal annealing was applied to reduce surface roughness to 3 nm (rms). The good optical performance of the arrays was confirmed by focusing and imaging tests. Complex 3D micro-optical elements over a footprint of 100 × 100 µ m 2 were ablated within 1 h (required for practical applications). A material removal speed of 120 µ m 3 / s ( 6 × 10 5 n m 3 / p u l s e ) was used, which is more than an order of magnitude higher compared to backside etching using a mask projection method. The method is applicable for fabrication of micro-optical components on transparent hard materials.

We systematically studied femtosecond laser-inscribed self-organized nanogratings and geometric phase elements such as a polarization diffraction focusing lens and Q-plate in sapphire crystal. Besides the void structures observed in the focus, nanogratings with periods of 150~300 nm were observed, depending on a nanoslit that took the role of a seeding effect by localized light field enhancement. The non-polarized refractive index change and birefringence were measured with values around 1 ∼ 2 × 10 − 3 and 6 × 10 − 4 , respectively. Based on the laser-inscribed form birefringence, a geometric phase lens and Q-plate were successfully demonstrated in sapphire with high imaging and a focusing effect. We expect that our findings may promote the understanding of laser-induced nanogratings in bulk and potential applications in geometric phase elements.

Herein, we report a kinoform phase-type lens (KPL), which is fabricated by femtosecond (fs)-laser-induced refractive index change inside sapphire crystal. By fabricating volume phase gratings in sapphire and measuring the energy ratio of the grating's first and second diffraction orders, the refractive index change in sapphire induced by fs-laser modification was obtained. Then a four-level KPL was designed and fabricated inside sapphire following the experimentally established scaling of the refractive index change and fs-laser power. Importantly, the KPL has unique UV focusing and imaging capability as well as a stable optical performance in different refractive index environments. The KPL embedded in sapphire has the same optical performance after a high-temperature (1050°C) annealing for 30 min. The KPLs in sapphire have great potential to increase light extraction efficiency in GaN blue-UV light-emitting diodes and can be used in micro-optical sensor applications in chemically harsh and high-temperature environments.

Fast fabrication of micro-optical elements for generation of optical vortex beams based on the q-plate design is demonstrated by femtosecond (fs) laser ablation of gold film on glass. Q-plates with diameter of ∼0.5 mm were made in ∼1 min using galvanometric scanners with writing speed of 5 mm/s. Period of gratings of 0.8 µm and groove width of 250 nm were achieved using fs-laser ablation at λ = 343 nm wavelength. Phase and intensity analysis of optical vortex generators was carried out at 633 nm wavelength and confirmed the designed performance. Efficiency of spin-orbital conversion of the q-plates made by ablation of 50-nm-thick film of gold was ∼ 3%. Such gratings can withstand thermal annealing up to 800 • C. They can be used as optical vortex generators using post-selection of polarisation.

Optical crystals are ideal materials for complex functional and durable optical components, but their good stability and hardness bring about difficulties in high‐precision machining and require surface roughness below λ/10. Femtosecond laser ablation is a widely applicable processing method indifferent to material types, but its 3D fabrication capability is limited by the accumulation of ablated debris and rough ablated surface. This work demonstrates a universal and flexible technology for the fabrication of crystalline micro‐optics with required shape and surface roughness for the most demanding optical phase control. The cavitation‐assisted ablation by a direct laser writing mode is followed by a high‐temperature treatment to remove the rough non‐crystalline layer caused by ablation. The annealing at temperatures below the melting point of the crystal reduces the roughness down to ≈2 nm without changing the structure shape. This virtue of maintaining the designed shape without change, which is impossible during thermal morphing of 3D surfaces of glasses, allows for a previously unavailable flexibility of surface finish for the most demanding optical micro‐optical elements made in this study. This universal technology with nanoscale resolution and free‐form 3D manufacturing capability is applicable for various crystals and provides a new way to fabricate micro‐/integrated‐optics and nonlinear optical elements.

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