Cylindrical Microlens Array Research Articles

In Situ Dewetting Assisted Plasma Etching of Large‐Scale Uniform Nanocones on Arbitrarily Structured Glass Elements

AbstractNanocones are ideal for wide‐angle antireflection of glass elements, yet their applications often encounter complex geometries and large sizes, bringing serious difficulty in developing a reliable and efficient manufacturing process. Here, an in situ dewetting assisted plasma etching (In situ DAPE) method is proposed to engrave nanocones on arbitrarily structured glass elements in one step. While exposed to high‐energy plasma, pre‐sputtered platinum (Pt) film undergoes dewetting, forming uniformly distributed nanoparticles that act as in situ sacrificial masks for plasma etching to generate nanocones. The nanocone size is decided by nanoparticle size, which can be modified through the Marangoni effect of the melted Pt film. Incorporating a passivation step can improve the aspect ratio of nanocones up to ≈8:1 due to the trench effect. Nanocones with diameters ranging from 62 to 136 nm and heights from 126 to 942 nm can be achieved. The nanocones help to achieve an average transmittance of 98% over the 0.3–2.5 µm spectrum and a 79.4% laser‐induced damage threshold of bare fused silica. The efficient fabrication of nanocones over multiple glass elements is demonstrated including a 2‐inch flat window, cylindrical microlens array, and diffractive grating, highlighting the efficacy of the In situ DAPE method for high‐performance optical elements.

Responsive Liquid Crystal Network Microstructures with Customized Shapes and Predetermined Morphing for Adaptive Soft Micro-Optics.

Stimuli-responsive materials have garnered substantial interest in recent years, particularly liquid crystal networks (LCNs) with sophisticatedly designed structures and morphing capabilities. Extensive efforts have been devoted to LCN structural designs spanning from two-dimensional (2D) to three-dimensional (3D) configurations and their intricate morphing behaviors through designed alignment. However, achieving microscale structures and large-area preparation necessitates the development of novel techniques capable of facilely fabricating LCN microstructures with precise control over both overall shape and alignment, enabling a 3D-to-3D shape change. Herein, a simple and cost-effective in-cell soft lithography (ICSL) technique is proposed to create LCN microstructures with customized shapes and predesigned morphing. The ICSL technique involves two sequential steps: fabricating the desired microstructure as the template by using the photopolymerization-induced phase separation (PIPS) method and reproducing the LCN microstructures through templating. Meanwhile, surface anchoring is employed to design and achieve molecular alignment, accommodating different deformation modes. With the proposed ICSL technique, cylindrical and spherical microlens arrays (CMLAs and SMLAs) have been successfully fabricated with stimulus-driven polarization-dependent focusing effects. This technique offers distinct advantages including high customizability, large-area production, and cost-effectiveness, which pave a new avenue for extensive applications in different fields, exemplified by adaptive soft micro-optics and photonics.

Conformal polishing of a glass microlens array through oxyhydrogen flame-induced viscoelasticity flow at nano/microscale

Glass microlens arrays with small unit sizes and high integration capacities are widely utilized in various optical systems, but the femtosecond laser milling produces microscale residual steps and nanoscale rough topography on microlens surface. Accordingly, an oxyhydrogen flame polishing is proposed after femtosecond laser milling, aiming to efficiently fabricate the ultrasmooth surface without damaging shape accuracy by triggering a viscoelasticity flow at nano/microscale. Through simultaneous modelling of the polishing process, a large thermal power results in a high viscoelasticity flow velocity for nanoscale topography smoothing, followed by microscale step melting. Then, a single-point polishing experiment is conducted to determine the critical transition temperatures for nanoscale smoothing and microscale melting. It is further experimentally applied to achieve an ultrasmooth surface of cylindrical microlens array with its roughness less than 0.2 nm and no hydroxyl introduction. This process also effectively repairs subsurface damage and reduces the form error to ±0.5 μm, improving the surface quality and shape accuracy. Similar results are also observed for the polishing of spherical microlenses. In conclusion, the method of combining femtosecond laser milling and oxyhydrogen flame polishing holds promise for high-efficiency and high-quality fabrication of glass components with micro features.

Cylindrical liquid crystal micro-lens array based on interdigital electrodes

ABSTRACT Based on the traditional structure of in plane switching liquid crystal display, a cylindrical liquid crystal micro-lens array driven by interdigital electrodes is proposed, and its performance is studied. Firstly, the director distribution and relative phase difference distribution of liquid crystal molecules were calculated, which shows that this structure can be used to fabricate cylindrical liquid crystal micro-lens. Then, by comparing lenses of difference sizes, it is found that narrow electrodes should be selected for lens production, and the centre of the electrode gap should be selected as the central axis of a single liquid crystal micro-lens. Finally, a certain electrode structure is selected to explore its focal length, focusing quality and zoom time. The results show that the focal length of the liquid crystal micro-lens decreases gradually with the increase of the driving voltage. When the driving voltage is between 3 Vrms and 5.5 Vrms, the liquid crystal micro-lens has good focusing quality, and its corresponding focal length changes from 1.63 mm to 20.28 mm. Based on this structure, when the liquid crystal lens is driven by the above two voltages alternately, the time required for liquid crystal molecules to reach stability is 2.35 s and 3.87 s respectively.

Fabrication of Cylindrical Microlens Array on RB-SiC Moulds by Precision Grinding with MAWJ-Textured Diamond Wheels

Cylindrical microlens array (CMA) is applied widely in imaging, sensing, and laser machining fields. Among the many techniques for machining CMA, moulding is considered a mass-production method with low-cost and good accuracy. Aimed at the present problems in the machining of CMA moulds, which include low processing efficiency and the prediction of the surface topography, this paper focused on the fabrication of CMA on RB-SiC moulds by precision grinding with micro-abrasive water jet (MAWJ) textured diamond wheels. The combined rough–fine grinding strategy for ceramic mould materials was proposed. The grinding experiments of CMA were carried out. The ultra-precision grinding method was optimized to obtain high shape accuracy and a high-quality surface of RB-SiC moulds. It was found that by using MAWJ-textured diamond wheels, the profile error in the peak-to-valley value (PV) of the CMA moulds can be further reduced to 6.7 μm by using the combined rough–fine strategy grinding process.

The Application of the Combination of Virtual and Reality in the Film Space Performance

In order to improve the effect of film space performance, this paper applies the combination of virtual and reality to the film space performance processing. Moreover, this paper analyzes the light field distribution of the three-dimensional object in space, and modulates the projected image projected on it with the spectral characteristics of the optical screen to finally restore the light field of the original object. In addition, this paper uses the multi-projection method to study the recovery process of the cylindrical microlens array screen to the light field, and divides and reorganizes the multi-view image of the scene shot by the camera array to obtain the correct projected image. Finally, this paper applies the space processing algorithm based on the combination of virtual and reality to the film space performance processing, and uses experimental research to verify the reliability of the method proposed in this paper.

Fabrication of cylindrical microlens array using rotatable multi-arrayed needle coating module for light out-coupling of OLEDs

We have performed coatings of poly(methyl methacrylate) (PMMA) using a rotatable multi-arrayed needle coating module to achieve high-density and high-aspect-ratio cylindrical microlens arrays (C-MLAs) for potential applications in organic light-emitting diodes (OLEDs). It is shown that high-density C-MLAs can be fabricated by rotating the coating module in such a way that the spacing between microlenses can be reduced (tuned). To enhance the aspect ratio of C-MLAs, we have analyzed the coating behaviors by varying the material parameters such as the molecular weight of PMMA, solute concentration, and wettability of the PMMA solution. It is demonstrated that high-aspect-ratio C-MLAs can be achieved using a coating solution with a small amount of a hydrophobic solvent, in which a high concentration of low-molecular-weight PMMA is dissolved. To further enhance the aspect ratio, we have come up with a new process method; repetitive coating and pre-drying treatment in ambient air. Such a repetitive coating method is shown to boost the microlens thickness without a much compromise on the microlens width. With this scheme, we have fabricated the C-MLA with the average thickness of 22.6 μm and width of 125 μm (aspect ratio as high as 0.18) at a coating velocity of 3 mm/s. The light out-coupling efficiency of OLED with the C-MLA increases by 20%, which is in good agreement with the result by ray tracing simulations.

Preparation method of silicon-based aspheric cylindrical microlens array

Preparation method of silicon-based aspheric cylindrical microlens array

3D Printing of a PDMS Cylindrical Microlens Array with 100% Fill-Factor.

Cylindrical microlens arrays (CMLAs) play a key role in many optoelectronic devices, and 100% fill-factor CMLAs also have the advantage of improving the signal-to-noise ratio and avoiding stray-light effects. However, the existing preparation technologies are complicated and costly, which are not suitable for mass production. Herein, we propose a simple, efficient, and low-cost manufacturing method for CMLAs with a high fill-factor via the electric-field-driven (EFD) microscale 3D printing of polydimethylsiloxane (PDMS). By adjusting the printing parameters, the profile and the fill-factor of the CMLAs can be controlled to improve their optical performance. The optical performance test results show that the printed PDMS CMLAs have good image-projecting and light-diffraction properties. Using the two printing modes of this EFD microscale 3D-printing technology, a cylindrical dual-microlens array with a double-focusing function is simply prepared. At the same time, we print a series of specially shaped microlenses, proving the flexible manufacturing capabilities of this technology. The results show that the prepared CMLAs have good morphology and optical properties. The proposed method may provide a viable route for manufacturing large-area CMLAs with 100% fill-factor in a very simple, efficient, and low-cost manner.

Fabrication of large-area cylindrical microlens array based on electric-field-driven jet printing

The cylindrical microlens array (CMLA) is an important micro-optical component, it has very significant application effects in the fields of naked eye three-dimensional display, laser line generation, and deformed beam shaping. However, the high efficiency and low-cost manufacturing of large-area CMLA is still challenging for industry and academia. Based on the electric-field-driven (EFD) jet printing technique, a new method for manufacturing a large-area CMLA with high efficiency and low cost has been proposed. We use the theoretical analysis and numerical simulation to investigate the basic principle of EFD jet printing. The influence of process parameters on the formation of CMLA was revealed by experiments. Using optimized process parameters, the fabrication of a CMLA with a patterned area of 50 × 50 mm2, a line width of 70 μm, and a period of 100 μm was achieved. The geometric and optical properties of the fabricated CMLA were characterized, showing that the products have the good geometric appearance and focusing effect. The results show that the proposed fabrication method provides a new manufacturing process for large-area manufacturing of CMLA with high efficiency and low cost.

Ultra-fast adaptive optical micro-lens arrays based on stressed liquid crystals

We characterized the optical properties of a photoresist-based micro-lens using a stressed liquid crystal matrix for high-speed variation of the focal distance. We also determined the operational parameters for the adaptive optical spherical and cylindrical micro-lens arrays. The resulting optical elements feature fast response times, around 1 ms, with a focal length range of 2600-970 μm.

Fabrication of high fill factor cylindrical microlens array with isolated thermal reflow.

We demonstrate a simple, controllable, and stable method for fabricating high fill factor cylindrical microlens array with a novel isolated thermal reflow process. In this method, microstripes with a very small gap were obtained via digital micromirror device-based lithography, then covered with polydimethylsiloxane (PDMS) solution. The prepared microstripes were isolated and were heated and reflowed to a cylindrical microlens array. During the reflow process, the semicross-linked PDMS can serve as a barrier to prevent the diameter change and the bonding of adjacent microlenses. By this special treatment, the fill factor of the cylindrical microlens array can be significantly improved. Moreover, the reflow time and temperature have very little effect on the microlens shape due to the surrounded semicross-linked PDMS. This will make our process stabler than traditional methods. The measured 3D profile is good and satisfactory, and excellent optical performance is demonstrated with the fabricated cylindrical microlens arrays. The proposed method may offer a viable route for fabrication of high fill factor microlens arrays in a very simple and stable way.

Controllable long focal length microlens based on thermal expansion.

A novel method to fabricate a microlens array with a long focal length has been developed in this paper. It is based on the fabricating and heating of a microlens consisting of two materials with a great difference in coefficient of thermal expansion. A thermal expansion process leads to considerable deformation of the microlens surface and significant increase in focal length, which could be controlled by altering the processing temperature. Cylindrical polymeric microlens arrays with different focal lengths were successfully fabricated. By measuring the focal length and temperature dependence of the cylindrical microlens geometry, the formation mechanism was analyzed and validated. While the temperature is ranged from 20°C to 50°C, the focal length of the cylindrical microlens has been extended by 38.2% and the longest focal length was obtained up to 6.6mm for the microlens with a linewidth of 240μm.

Optimal condition for employing an axicon-generated Bessel beam to fabricate cylindrical microlens arrays

A numerical algorithm, modelling the transformation from a Gaussian beam to a Bessel beam, is presented for the purpose to study the optimal condition for employing an axicon-generated Bessel beam to fabricate cylindrical microlens arrays (CMLAs). By applying the numerical algorithm to simulate the spatial intensity distribution behind the axicon under different defects of a rotund-apex and different diameter ratios of an incident beam to the axicon, we find that the diffraction effects formed by the axicon edge can be almost eliminated when the diameter ratio is less than 1:2, but the spatial intensity distribution is disturbed dramatically even a few tens of microns deviation of the apex, especially for the front part of the axicon-generated Bessel beam. Fortunately, the lateral intensity profile in the rear part still maintains a desirable Bessel curve. Therefore, the rear part of the Bessel area and the less than 1:2 diameter ratio are the optimal choice for employing an axicon-generated Bessel beam to implement surface microstructures fabrication. Furthermore, by applying the optimal conditions to direct writing microstructures on fused silica with a femtosecond (fs) laser, a large area close-packed CMLA is fabricated. The CMLA presents high quality and uniformity and its optical performance is also demonstrated.

Fabrication of parabolic cylindrical microlens array by shaped femtosecond laser

A simple and efficient technique for fabricating parabolic cylindrical microlens arrays (CMLAs) on the surface of fused silica by shaped femtosecond (fs) laser direct-writing is demonstrated. By means of spatially shaping of a Gaussian fs laser beam to a Bessel distribution, an inversed cylindrical shape laser intensity profile is formed in a specific cross-sectional plane among the shaped optical field. Applying it to experiments, large area close-packed parabolic CMLAs with line-width of 37.5 μm and array size of about 5 × 5 mm are produced. The cross-sectional outline of obtained lenslets has a satisfied parabolic profile and the numerical aperture (NA) of lenslets is more than 0.35. Furthermore, the focusing performance of the fabricated CMLA is also tested in this work and it has been demonstrated that the focusing power of the CMLA with a parabolic profile is better than that with a semi-circular one.

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.

Extrusion printing for fabrication of spherical and cylindrical microlens arrays.

In this paper, we present an extrusion printing technique for producing spherical and cylindrical plano-convex microlens arrays with controllable feature dimensions. This technique employs a robotic adhesive dispenser for robotically controlled microextrusion of ultraviolet (UV) curable polymer onto a glass substrate surface to directly deposit the microlens arrays. It provides a simple and flexible alternative to fabricate both spherical and cylindrical microlens arrays.

Rapid fabrication of cylindrical microlens array by shaped femtosecond laser direct writing

In this study, a remarkable spatial shaping approach is proposed to transform Gaussian femtosecond laser into quasi-Bessel optical field with compressed central lobe and amplified side lobes of the spatial intensity profile. Based on this technique, inward bulge trench (IBT) structures are fabricated with high efficiency on the surface of PMMA by a single illumination step, whose cross-sectional profile is opposite to the results fabricated by Gaussian beam. And plano-convex cylindrical microlens array, which is consistent in size and shape throughout a large sample area, is formed through simply piecing together the IBT structures during fabricating process. Furthermore, numerical simulations of optical field in radial direction and on-axial direction are exploited to rationalize the dependence of the patterned microstructures on the spatial intensity distribution of femtosecond laser.

Assessment of replication fidelity of optical microstructures by hot embossing

This work reports the performance evaluation of low-cost hot embossing processes of fine three-dimensional microstructures, namely (i) cylindrical microlens array, (ii) plano-convex aspheric Fresnel lens, and (iii) pyramidal array structures. All those optical elements were replicated by employing a low-cost hot embossing tool in optical quality acrylic material. Scanning electron microscopy and optical interference microscopy techniques were used to quantitatively measure the obtained structures. In terms of the replication fidelity with respect to the mold counterpart, the resulting optical elements presented at least 96 % of dimensional fidelity at micro- and nanometer scale, including the structures with sharp edges present in the Fresnel lens. In terms of the surface optical quality, resulting root mean square surface roughness of at least one tenth of wavelength was obtained, considering applications in the visible range of spectrum. The results showed that even nanostructures generated by the material removal mechanisms during mold fabrication, such as crystal grain elastic recovery, were well replicated with differences in the range of few of nanometers which is within the vertical resolution of the employed optical interference technique.

Formation of cylindrical micro-lens array on fused silica glass surface using CO2 laser assisted reshaping technique

Abstract This paper demonstrates the laser assisted formation of plano-convex cylindrical and flat-top curved micro-lens array on fused silica glass surface. Initially, femtosecond laser pulses are irradiated on the sample glass to fabricate periodic linear micro-gratings on the glass surface. Afterwards, we reshape the micro-gratings by several times irradiation of a CO 2 laser beam by focusing the laser beam on top of the micro-gratings. As a consequence, plano-convex cylindrical micro-lens array with a period varying from 20 to 40 µm are formed on fused silica glass surface. However, flat-top curved gratings’ array is observed on the glass surface for a gratings’ period of 50 µm. The fabricated micro-lenses show great consistency in size and shape throughout the sample area. Furthermore, we analyze the formation mechanism of micro-lens array on glass surface using the CO 2 laser assisted reshaping technique. The proposed reshaping technique exhibits great potential for forming a large variety of micro-lens arrays on the surface of various transparent materials.