Fabrication of a bionic compound eye on a curved surface by using a self-assembly technique.

Microlens arrays on curved surfaces are regarded as critical elements of bionic compound eyes (BCEs), which exhibit the comparative advantages of a wide field of view and tracking fast-moving objects. However, the fabrication of a curved microlens array is still challenging. Along these lines, in this work, a straightforward, rapid, and low-cost technique for the fabrication of curved microlens arrays is reported by using the self-assembly technique. A reactive ion etching process treated the surface of the curved polydimethylsiloxane (PDMS) substrate to generate a hydrophobic-hydrophilic pattern. Then, the curved microlens array can be realized by dewetting a liquid glue onto the substrate using the dip-coating method and followed by crosslinking. The proposed BCE structure consists of 2400 microlenses (400 - µm diameter and 440 - µm center distance) arranged in a hexagonal configuration on a curved PDMS surface (34 - mm diameter and 40.4 - mm curvature radius). A field-of-view of 50° was demonstrated, which has potential applications in various fields including imaging sensors, medical diagnostics, machine vision systems, and photodetectors.

Liquid crystal microlens array with positive and negative focal lengths based on a patterned electrode.

A liquid crystal microlens array (LCMLA) with positive and negative focal lengths based on a ring-array patterned electrodes is demonstrated. By carefully designing patterned electrodes with a circular electrode array area and outer ring electrode region area, the switching of the positive and negative lens effect can be easily achieved in a single cell. A positive lens effect appeared when the voltage was applied to the outer ring electrode region and the top substrate. The focal length changed from infinity to 1 mm as the voltage varied from 0 to 3Vrms. A negative lens effect occurred when the voltage was applied to the circular electrode array and the top substrate. The focal length varied from infinity to -1mm when the voltage changed from 0 to 2Vrms. The imaging properties of the LCMLA at different voltages are evaluated. Our LCMLA, with simple structure, low driving voltage, and good stability, has potential applications in optical communication, imaging processing, and displays.

Vari-focal liquid microlens array using an electrically responsive fluid actuated by a ring array patterned electrode.

A transparent fluid dibutyl adipate (DBA) is suitable for fabricating the adaptive lens due to its unique deformation under a direct current (DC) electric field. In this report, a DBA liquid microlens array (LMA) with a tunable focal length is demonstrated. A hydrophobic layer deposited in the ring array patterns on the electrode induced the formation of the DBA liquid microdroplets array self-assembly. The electronegative DBA liquid tends to move to the anode at a DC voltage. The proposed DBA LMA with a diameter of 100 µm can change its focal length from 0.92 to 1.42 mm when the voltage changes from 0 to 200 V. The response time is relatively fast (∼790m s). Due to the high optical transmittance (∼91%) and good thermal stability in the temperature range of -24.8-161.5∘C, our DBA LMA shows good focusing properties and has potential applications in the field of image processing, portable electronic devices, beam steering, ophthalmology, and 3D displays.

Large-Area and Rapid Fabrication of a Microlens Array on a Flexible Substrate for an Integral Imaging 3D Display.

A curved integral imaging three-dimensional (3D) display attracts a lot of interest due to its enhanced 3D sense of immersion and wider viewing angle. In this paper, a microlens array (MLA) based on a flexible poly(ethylene terephthalate) (PET) substrate was achieved by a straightforward, rapid, and low-cost technique. The reactive ion etching (RIE) process treated PET/CYTOP covered with a flexible mask to generate a hydrophilic-hydrophobic patterned surface. The well-designed arrays of confined adhesive droplets with a controlled geometry on a hydrophilic-hydrophobic patterned surface were formed using the blade-coating method. A flexible MLA with a diameter of 820 µm, a size of 5.3 cm × 5.1 cm, and a radius of curvature of 25 cm was fabricated and combined with a curved two-dimensional (2D) monitor to realize a lateral viewing range of 6.4 cm at a viewing distance of 25 cm, which is 4 times larger than with flat integral imaging 3D display system. The flexible MLA has the advantages of a controllable lens profile and large pitch, and it can be manufactured on a large scale. In addition, it provides a large viewing angle for the reconstructed 3D image.