Fabrication of large curvature microlens array using confined laser swelling method

Microlenses arrays: Fabrication, materials, and applications

Microlenses have become an indispensable optical element in many optical systems. The advancement of technology has led to a wider variety of microlenses fabrication methods, but these methods suffer from, more or less, some limitations. In this article, we review the manufacturing technology of microlenses from the direct and indirect perspectives. First, we present several fabrication methods and their advantages and disadvantages are discussed. Then, we discuss the commonly used materials for fabricating microlenses and the applications of microlenses in various fields. Finally, we point out the prospects for the future development of microlenses and their fabrication methods.

Designable Ultratransparent and Superhydrophobic Surface of Embedded Artificial Compound Eye with Extremely Low Adhesion

Real-world implementation of artificial compound eye (ACE) has been limited by its poor transparency and high requirement for the stable Cassie state. In general, the improvement of surface dewetting performance sacrifices the transparency of ACE. Herein, ACE was obtained by an integrated manufacturing technology that combined photolithography, microprinting, and chemical growth. Through skillful manipulation of the fabrication process, dewetting hairs were fabricated on the top of micropillars and around the microlens. The combination of nanohairs and micropillars resulted in outstanding superhydrophobicity (∼170°), pristine lotus effect with low sliding angle (∼1°), and contact angle hysteresis (∼2°). Moreover, the surface showed almost no adhesion under a preload of 4 mN, exhibiting excellent stable Cassie state and antiadhesion performance. Furthermore, dynamic impact showed that the impacting droplet was quickly detached from the surface (contact time ∼14.1 ms) without sticking for We = 60. The designed transparency resulted in high performance of optical unit (∼99%, bare glass for comparison). Moreover, ACE exhibited better focusing and imaging capability under larger aperture diameter than microlens without nanohairs. We envision that this research presents a significant advancement in imparting superhydrophobicity and transparency to a so-far inapplicable family of optical devices for many practical outdoor applications.

Fabrication of Artificial Compound Eye with Controllable Field of View and Improved Imaging

Many arthropods have compound eyes, which are made up of numerous separate visual units (microlenses) or ommatidia. These natural compound eyes have exceptional optical properties such as wide field of view (FOV), low aberration, and fast motion tracking capability. In this paper, a large-scale artificial compound eye (ACE) is fabricated efficiently using a combination of inkjet printing and air-assisted deformation processes. Both size and geometry of the microlens are controlled via superposed drops on the substrate. The simulation results show that the light intensity of the ACE follows a systematic distribution for tilted incident light, which represents a significant improvement, compared to planar distributed microlenses. We then manufacture ACEs with different heights and diameters, and their FOVs are compared with the theoretically predicted results. The measured FOV was 50°-140°. The acceptance angles for the different ACEs are determined, and their relationship with the ratio of height to radius (H/r) of the microlens is investigated in more detail. Furthermore, the imaging properties of the microlenses with different angles of incidences are studied, which suggest a FOV up to 140° and an acceptance angle of about 50°. The microlens captures images even at an angle of incidence of about 60°. The corresponding distortion in both the x and y directions is also investigated. Our findings provide guidelines for the development and fabrication of ACEs with large FOVs and acceptance angles, which may find applications in military, robotics, medical imaging, and astronomy.

Fabrication of Hierarchical Micro/Nano Compound Eyes

Fabrication of a hierarchical macro-/micro-/nano compound eye is presented in this paper. This bioinspired compound (BIC) eye is obtained by an integrated manufacturing technology that combines (i) nanoimprinting, (ii) picosecond laser swelling, and (iii) air-assisted deformation. The diameter and height of nanopillars, microlens, and macrobase can be controlled precisely by fine-tuning the process parameters. The multifunctional properties of the BIC eye, such as superhydrophobicity, antireflection, and other optical characteristics, are investigated. It is found that the microlens with nanopillars can effectively improve the surface wettability with a contact angle of 152° and contact angle hysteresis of 12°, and enhance transmittance by 2% over the wavelength range of 200-1200 nm. Moreover, the final hierarchical compound eye exhibits the excellent imaging properties and a wide field-of-view of 120° without distortion. These multifunctional properties will enable the widespread application of the compound eye in diverse real-time environmental conditions.

Artificial Compound Eyes Prepared by a Combination of Air-Assisted Deformation, Modified Laser Swelling, and Controlled Crystal Growth

This study presents the manufacturing process of bioinspired compound (BIC) eyes. The hierarchical eyes were accomplished by a combination of (i) modified laser swelling, (ii) air-assisted deformation, and (iii) controlled crystal growth. The results show that the addition of nanostructures on the surface effectively improved the water repellent performance with a contact angle (CA) of ∼160° and generally decreased the reflection by ∼25% in the wavelength range of 400-800 nm than the planar surface. Apart from these properties, the BIC eyes showed good optical performance. The convex structure has a circular shape and aspherical profile; this provides optical uniformity and constant resolution (full width at half-maximum = 1.9 μm) in all the directions. Furthermore, the BIC eyes reduced the imaging distortion by 1.5/3.4 and 2.3/3.1 times along the x and y axes, respectively, under 10° and 20° incident lights than a single lens. In the light acceptance range, the image displays almost no distortion.

Femtosecond laser one-step direct-writing cylindrical microlens array on fused silica

We demonstrate an efficient method for fabricating high-quality cylindrical microlens arrays (CMLAs) on the surface of fused silica, fully based on spatially shaping of a femtosecond laser beam from Gaussian to Bessel distribution. As the envelope of shaped spatial intensity distribution matches the profile of cylindrical microlens perfectly, a CMLA with more than 50 uniform microlenses is fabricated by simple line scanning. The radius and height of these microlens units can be finely controlled by adjusting the power of laser pulses. Excellent optical imaging and high-speed fabrication performances are also demonstrated by our fabricated CLMA.

Role of space charges inside a dielectric polymer in the electrohydrodynamic structure formation on a prepatterned polymer (ESF-PP)

Mushroom-shaped structures with a high aspect ratio are fabricated based on the action of space charges inside the dielectric polymer.

λ/20 axial control in 2.5D polymerized structures fabricated with DLW lithography

An astonishing λ/20 height control is accomplished in 2.5D photopolymerized structures by taking advantage of the induced expansion of the resin. Our nanofabrication method is a one-pot approach with two processing steps: (i) regular 2.5D photopolymerization of the resin monomer by using multiphoton direct laser writing (DLW) lithography and (ii) spatially-selective irradiation of the photopolymerized features before development resulting in a nanometer-controlled height increase of the structure. The UV-visible-NIR sub-wavelength axial feature size (~40 nm) of this method allows fabricating devices with applications in multiple technological fields such as nanoelectronics and photonics.

Focal varying microlens array

We report a novel microlens array with different curvature unit lenses (MLADC) fabricated with femtosecond laser direct writing technology. The MLADC consisted of hexagonal hyperboloid unit microlenses, which have different heights and curvatures from others. The unique optical performance of imaging and focusing capability were demonstrated. An object was imaged at different positions from the MLADC by unit lenses, as the ability of adjusting the curvature of the image plane for overall MLADC. In addition, the experiment had a good agreement with simulation results, which was based on the analysis of the finite element method. The novel MLADC will have important applications in improving the performance of optical systems, especially in field curvature correction and real-time three-dimensional imaging.

A novel thermal reflow method for the fabrication of microlenses with an ultrahigh focal number

A novel thermal reflow method for the monolithic fabrication of microlens arrays with ultrahigh focal numbers and tunable lens profiles.

Lateral flow through a parallel gap driven by surface hydrophilicity and liquid edge pinning for creating microlens array

This letter proposes a surface-energy driven process for economically creating polymer microlens array (MLA) with well controllable curvatures. When a UV-curable prepolymer flows into a cell constructed by multiple holes on a top template and a flat substrate, since the edge pinning of the contact line, an array of curved air/prepolymer interface forms around each microhole of the template. Then a UV-radiation of the bulk prepolymer leads to a solid microlens array. The curvature of the air/prepolymer interface can be controlled by choosing materials with different interface free energy or varying the gap height mechanically.

Rapid method for fabricating polymeric biconvex parabolic lenslets

Microlenslets as well as microlens arrays have shown tremendous attractions and successes in miniature optical systems in recent decades. However, the fabrication methods for microlenslets and microlenslet arrays are limited. In this Letter, a rapid and low-cost method for fabricating polymeric biconvex lenslets is presented. This newly developed process is simply based on wetting behavior at interface and is able to produce high-quality biconvex lenslets with controllable size and shape. This technology will greatly simplify the production process and reduce the manufacturing costs for micro-optics.

Rigorous microlens design using vector electromagnetic method combined with simulated annealing optimization

In this paper, finite-aperture diffractive optical element with its critical dimension smaller than illumination wavelength is modeled and optimized using an integrated method. This method employs rigorous analysis model based on Finite Difference Time Domain (FDTD), and simulated annealing (SA) global search algorithm. Numerical results reveal that the diffraction efficiency of the 8-step microlens quickly climbs to its global optimum along with the optimization process, which manifests its global search ability. The design algorithm and implementation are discussed in details. Considering its time consuming efficiency and global search ability, our method provides valuable reference value in practical multistep microlens design.