The fabrication of high filling factor double side micro lens array with high alignment accuracy

We demonstrate the depth measurement method of holographic images using integral imaging. The depth information of holographic images can be obtained with a single capture by conventional integral imaging pickup system composed of a micro lens array (MLA) and an image sensor. In order to verify the feasibility of our proposed method, an elemental image set of holographic images formed by a MLA was generated by a computer, and then refocused images at different planes were reconstructed numerically using computational integral imaging reconstruction (CIIR) technique for depth measurement. Note that we set the distance between MLA and image sensor as focal length of micro lens for large depth of focus. From the numerical results, we can measure the depth representation of holographic images successfully. However, refocused images from an optically captured elemental image set provide poor depth discrimination due to expected error in distance between MLA and image sensor. Only an object in a particular narrow depth range can be focused clearly when the image sensor is placed out of the MLA focal plane. The simulated results in this condition matched reasonably with the experiment result.

Integral imaging (II) is a technique capable of displaying 3-D images with continuous parallax in full natural color through micro-lens array. II was firstly proposed by Lippmann about one century ago. With recent progress in the theory and micro-lens manufacturing, it is becoming the most practical and prospective 3D display technique in developing next generation three-dimensional TV (3DTV) and visualization fields. Among many problems of II the resolution issue is still the focus. The resolution of the reconstructed 3D image is determined by many parameters. Up to now various factors such as the size and the pitch of lens array, the distance between the apertures, the resolution of the CCD camera and the display device have been analyzed. How the non-ideal display lens array will affect the reconstructed 3-D image in geometrical position and quality is discussed in this paper. The non-ideal display lens array with equal gap and surface refraction in integral image reconstruction are analyzed. The relation between image shift, diffusion length in depth direction and the ideal original position are derived. Analysis results prove that the farther the 3-D image is reconstructed from the lens array, the more significant the image shift and diffusion become. Moreover, a reconstructed 3-D image diffuses in depth direction is more remarkable with the just refractive lens array. Based on the theoretical analysis, preliminary simulated experiments are conducted to confirm our conclusions with optical software ASAP and spot diagram. The results will play an important role in optimum parameters designing and further data processing of the next generation II-based 3DTV.

Microporous polymer films with a hexagonal arrangement of pores were prepared by simple casting of various polymer solutions under humid conditions. Hexagonally packed micropores were prepared by using condensed water droplets as templates on the surface of polymer solutions. Spherical micro lens arrays (MLAs) were fabricated simply by molding from the resulting honeycomb structures. By peeling off the upper layer with adhesive tape, the pillars were severed, forming pins on each layer, and a hexagonal array of pincushion structures was generated by this procedure. Hemispherical MLAs were also fabricated by molding the pincushion structures. The hemispherical MLAs projected clearer miniaturized images than spherical MLAs.

In recent years, the moiré imaging device has become one of the hot topics in the field of micro optics due to its strikingly visual three-dimensional (3D) effect which can be easily recognized by naked eye. Traditionally, the moiré imaging film is composed of the superposition of a microlens array（MLA）and a micro pattern array (MPA）with high alignment accuracy. By the combination of the nanoimprinting and nanoprinting techniques, we fabricated a moiré imaging film on a large-format substrate characterized by fluorescent enhancement effect under ultraviolet light illumination. By using a novel virtual mask technique, the MPA can contain more information than traditional one. It is worthy to note that the nanostructure is introduced to the MPA to promote the light efficiency of the fluorescent material. A synthetically magnified moiré image with 3D effect is demonstrated. The moiré imaging film has widely potential applications in 3D imaging, optical anti-counterfeiting, packaging, etc.

Microlens arrays play a critical role in enhancing imaging systems due to their outstanding optical performance, compact size, and lightweight nature. However, traditional fabrication methods for microlens arrays suffer from low precision, inefficiency, high costs, and a lack of adequate surface figure control. In this paper, we present a novel approach for microlens array fabrication, using a projection lithography process with mask-shifting. The method employs a 0.2× projection objective lens to enhance linewidth resolution. By employing a projection-based mask-shift filtering technique, we achieve superior surface figure accuracy while reducing the complexity of mask preparation. The experimental results for four microlenses with different aperture sizes demonstrate surface figure accuracy in the submicron range and surface roughness at the nanometer level. In addition, 3D profilometer scanning equipment was employed to measure the surface roughness of these microlens arrays, and the measurement results of these microlens arrays processed using the proposed method for their surface roughness are 18.4 nm, 29.6 nm, 34.4 nm, and 56.1 nm. Our findings indicate that this method holds great potential in microlens array fabrication, offering the ability to achieve lower linewidths and higher surface figure accuracy compared to conventional methods.

A novel method for fabrication of self-aligned double microlens arrays

This paper describes microlens arrays implemented on a flexible substrate. For the first time, we have demonstrated binary Fresnel zone plates fabricated from silicon nanowires embedded in a PDMS matrix. Lens arrays on flexible substrates can potentially benefit from an increased field of view, which is important for applications such as microscopy and surveillance. Lens arrays have wide applications in 3D displays, LCD projectors, optical switches and tunable lasers. We report our design, fabrication and imaging demonstration for silicon based microlens arrays.

The ability to use chalcogenide glass thin films as photoresists for one-step maskless grayscale lithographic patterning is demonstrated. It is shown that the chalcogenide photoresists can be used to fabricate grayscale patterns with smooth and continuous profiles such as arrays of cylindrical and spherical microlenses, which are useful as optical structures for IR applications. The etching and exposure parameters are optimized to obtain smooth reproducible lens arrays of 150 μm periodicity and up to ∼170 nm height on large areas (∼1 cm(2)). The roughness is found to increase as a function of the exposure dose and is attributed to the selective dissolution of the As-Se, As-As, and Se-Se bonds present in the nanodistributed phases and the presence of the oxide phase. Thus, a minimum exposure dose produces optimally patterned lens arrays. The focal length calculated for the smooth microlens array is ∼9.3 mm, indicating the suitability of the lens arrays for focusing applications in the IR region.

Single-crystal silicon microlens arrays are increasingly required in advanced infrared optics. In this study, the authors attempted to fabricate hexagonal microlens arrays, which offer high optical efficiency, on a single-crystal silicon wafer using diamond turning. A tool-servo driven segment turning method was proposed to reduce the dynamic error of the machine tool induced by lenslet edges during lens array cutting. From the results of both cutting experiments and theoretical analysis of the machine tool dynamic error, it was demonstrated that the segment turning method reduced significantly the dynamic errors and led to high form accuracy. As a result, sharp edges among the lenslets were generated precisely and microlens arrays with a form error of ~300 nm peak-to-valley and surface roughness of ~5 nmSa, which meets the requirements of infrared optical systems, were successfully fabricated. The subsurface damage, such as the amorphization of silicon, caused by machining was also reduced.

Single-point diamond cutting is an efficient method to fabricate microlens arrays (MLAs). However, machining MLAs at the microscale with high dimensional accuracy and a smooth surface finish is a difficult task. In this study, a method of profile cutting is proposed to machine MLAs on electroless nickel–phosphorus (Ni–P) plating. To improve the dimensional accuracy of MLAs, a precision tool setting method is introduced, via which the precision of MLA sag can be controlled to within 20 nm. In addition, the formation mechanism of corrugation defects is studied via a finite element (FE) simulation of the wedge nano-cutting process and a cutting experiment of concentric ring grooves. By optimizing the tool settings and the machining parameters, high-quality MLAs with apertures of Φ100 μm can be created.

This work reports the fabrication of Fresnel Zone Plates (FZP) by employing a maskless lithography tool based on direct laser writing. The target application areas in this work are to use a micro lens array (MLA) in a wavefront sensor, for optical aberrations quantification in human eye diagnostics or adaptive optical system. This last one is essential in astronomy applications in order to correct the aberrations introduced by earth atmosphere. The fabricated FZP generates illumination points with high-contrast intensity in the focal plane, which is the purpose of the wavefront sensor. This high-contrast image suggests that the employed fabrication process is well controlled and it matches the design parameters.

Micromachining of transition metal ion doped glass surface by using a pulsed Nd:YAG (532 nm) laser for the optical device

The integral imaging microscopy system provides a three-dimensional visualization of a microscopic object. However, it has a low-resolution problem due to the fundamental limitation of the F-number (the aperture stops) by using micro lens array (MLA) and a poor illumination environment. In this paper, a generative adversarial network (GAN)-based super-resolution algorithm is proposed to enhance the resolution where the directional view image is directly fed as input. In a GAN network, the generator regresses the high-resolution output from the low-resolution input image, whereas the discriminator distinguishes between the original and generated image. In the generator part, we use consecutive residual blocks with the content loss to retrieve the photo-realistic original image. It can restore the edges and enhance the resolution by ×2, ×4, and even ×8 times without seriously hampering the image quality. The model is tested with a variety of low-resolution microscopic sample images and successfully generates high-resolution directional view images with better illumination. The quantitative analysis shows that the proposed model performs better for microscopic images than the existing algorithms.

Ultra-precision noncircular optical components, e.g. hyperbolic quadrupole in mass spectrometer, can be machined by diamond turning assisted by slow tool servo (STS). However, the bandwidth of STS is usually small, which limits the STS's capability in following the required tool path, leading to a large form error. To reduce the form error, this paper proposes an approach to apply variable spindle speed (VSS) to STS-based turning. Design of the VSS trajectory based on the noncircular profile of the optical component was investigated in detail. To validate the proposed approach, simulation on the application of VSS in the STS-based turning process was established and applied to the machining of typical noncircular optical components. Simulation results show that the proposed approach is effective in reducing the requirement on the bandwidth of the STS, resulting in higher form accuracy of the machined noncircular optical components.

A microlens array has become an important micro-optics device in various applications. Compared with traditional manufacturing approaches, digital light processing (DLP)-based printing enables fabrication of complex three-dimensional (3D) geometries and is a possible manufacturing approach for microlens arrays. However, the nature of 3D printing objects by stacking successive 2D patterns formed by discrete pixels leads to coarse surface roughness and makes DLP-based printing unsuccessful in fabricating optical components. Here, we report an oscillation-assisted DLP-based printing approach for fabrication of microlens arrays. An optically smooth surface (about 1 nm surface roughness) is achieved by mechanical oscillation that eliminates the jagged surface formed by discrete pixels, and a 1-3 s single grayscale ultraviolet (UV) exposure that removes the staircase effect. Moreover, computationally designed grayscale UV patterns allow us to fabricate microlenses with various profiles. The proposed approach paves a way to 3D print optical components with high quality, fast speed, and vast flexibility.