In lensless imaging, encoding the diffraction field recorded by the detector by adding a laterally or axially moving mask is the most common configuration. In this paper, we propose a new scheme for improving the speed and accuracy of complex object reconstruction. Particularly, a random binary amplitude mask is placed upstream of the object and moves obliquely to introduce speckle illumination on the object plane. The object and the detector are stationary in the experiment. Inspired by the idea of ptychography, the extended ptychographic iterative engine algorithm is adopted to reconstruct the object and unknown mask simultaneously. It is verified by simulation that our proposed method can improve the reconstruction resolution of the complex object compared with the conventional method. Further, the relevant parameters of the proposed scheme are also optimized. This improvement will facilitate the widespread application of lensless imaging in biology and materials science.
Multi-distance phase retrieval represents a computational imaging technique that synergizes a basic imaging setup with computational post-processing. This method involves capturing diffraction intensity at distinct distances, enabling the iterative reconstruction of the target's wavefront by incorporating the intensity patterns into the relevant algorithm. Despite the advantages of lensless imaging through multi-distance phase retrieval, including its uncomplicated setup, expansive field of view, and freedom from aberrations, challenges persist in terms of sluggish convergence and limited resolution. To address these concerns, the presented paper introduces enhancements to both the imaging system and the algorithm. This dual approach contributes to a remarkable 5.88 times acceleration in convergence speed, all achieved without the need for supplementary equipment. Moreover, a substantial enhancement in imaging quality is achieved when compared to the conventional method.
This article simulates a study on a phase recovery technique that combines triangular aperture illumination as a supporting constraint and partially overlapped random binary amplitude modulation. Inspired by the concept of ptychography, a random binary amplitude mask is designed with partially transparent regions that overlap each other randomly. The overlapping regions of the amplitude modulation mask impose a strong constraint on the coherence of the light field, similar to the overlap constraint in ptychography. Moreover, the redundant information brought by the overlapping binary masks can improve the reconstruction accuracy, and the triangular aperture constraint enables faster convergence in the method. Compared with the original binary amplitude modulation method, this constraint leads to higher convergence accuracy and speed in the iterative algorithm.
KEYWORDS: 3D image processing, 3D acquisition, Image processing, Microlens array, Cameras, Microlens, Imaging technologies, Imaging systems, 3D modeling, 3D applications
The traditional imaging method can only obtain the two-dimensional information of the object space in lateral resolution through a single exposure, but cannot obtain the longitudinal depth information. The depth information of the object space will be lost because the object cannot be reconstructed in three dimensions. The light field imaging technology enables reconstruction of three-dimensional objects by means of adding microlens arrays into a conventional camera system. The technology has a wide range of applications in medical, military, and entertainment. In this paper, a light field acquisition technology using microlens based on 3ds Max is proposed. A 3D object model was established using 3ds Max. By establishing a virtual microlens array, the crosstalk-free, high resolution and fast acquisition of the light field image by the microlens can be realized. Simulation study of the light field imaging technology can provide a highefficiency computational study. The acquired images are processed to reconstruct images from different perspectives. Finally, the light field imaging experiments based on microlens arrays is carried out to realize the image reconstruction in different perspective images. Reliability of the algorithm is verified.
Bionic compound eye optical element composed of multi-dimensional sub-eye microlenses plays an important role in miniaturizing the volume and weight of an imaging system. In this manuscript, we present a novel structure of the bionic compound eye with multiple focal lengths. By the division of the microlens into two concentric radial zones including the inner zone and the outer zone with independent radius, the sub-eye which is a multi-level micro-scale structure can be formed with multiple focal lengths. The imaging capability of the structure has been simulated. The results show that the optical information in different depths can be acquired by the structure. Meanwhile, the parameters including aperture and radius of the two zones, which have an influence on the imaging quality have been analyzed and discussed. With the increasing of the ratio of inner and outer aperture, the imaging quality of the inner zone is becoming better, and instead the outer zone will become worse. In addition, through controlling the radius of the inner and outer zone independently, the design of sub-eye with different focal lengths can be realized. With the difference between the radius of the inner and outer zone becoming larger, the imaging resolution of the sub-eye will decrease. Therefore, the optimization of the multifocal structure should be carried out according to the actual imaging quality demands. Meanwhile, this study can provide references for the further applications of multifocal microlens in bionic compound eye.
The high-precision fabrication of micro-/nano-structure is a challenge. In this paper, we proposed a new fabrication method of high-precision structure based on an etching resistance layer. The high-precision features were fabricated by photolithography technique, followed by the etching process to transfer the features to the substrate. During this process, the etching uniformity and error lead to the feature distortion. We introduced an etching resistance layer between feature layer and substrate. The etching process will stop when arriving at the resistance layer. Due to the high precision of the plating film, the high-precision structure depth was achieved. In our experiment, we introduced aluminum trioxide as the etching resistance layer. The structures with low depth error of less than 5% were fabricated.
According to the exposure pattern distortion in contact printing caused by the photoresist and sometimes has a rough surface with impurity particles on it, we propose a new flexible hybrid mask for contact printing. The mask consists of three layers: a flexible polymer buffer layer, a polymer structure layer of high Young's modulus, and a metal masking layer. Because the hybrid mask skillfully combines the characteristics of flexible polymer and high Young's modulus polymer, it has two advantages: high flexibility and high resolution. The flexible hybrid mask can attach closely with the photoresist under the condition of vacuum adsorption. So the fabrication of micro-nano structures with high precision and high resolution can be realized. In this paper, a new flexible hybrid mask with critical dimension of 2um was fabricated. The photoresist structure with high precision was manufactured using this mask by photolithography and it verified the feasibility of the mask for lithography.
With the advantages of small structure and high efficiency, the diffractive element is widely used in the construction of a structured light 3D measurement system. But the working wavelength of diffraction element is single, and the light field generated by the diffraction element is only one channel. We make the original single channel into three channels, so as to achieve from the serial algorithm to parallel algorithm to improve the measurement speed. Based on the lattice light field and the design method of multi wavelength diffraction elements, and in the premise of ensuring the number of points, the traditional lattice points of light field are divided into three channels. These channels are regarded as the target fields, and the diffraction element for generating color structure light field is designed.
This paper demonstrates an approach to fabricate nano-pillar based on thiol-ene via soft-lithography. The template is anodic aluminum oxygen (AAO) with ordered nano-holes with the diameter of 90nm.The nano-pillar consists of rigid thiol-ene features on an elastic poly(dimethylsiloxane) (PDMS) support. It is capable of patterning both flat and curved substrate. The thiol-ene is a new green UV-curable polymer material, including a number of advantages such as rapid UV-curing in the natural environment, low-cost, high resolution, and regulative performance characteristic. Here, we fabricated a two-layer structure, which included rigid thiol-ene nano-pillar with sub-100nm resolution and soft PDMS substrate. The experiment results show that this approach can be used to fabricate high-resolution features and the thiol-ene is an excellent imprint material. The fabrication technique in this paper is simple, low-cost, high-resolution and easy to high throughput, which has broad application prospects in the preparation of nanostructures.
In this paper, a quite effective method is proposed for designing the diffractive optical element (DOE) to generate a pattern with large diffraction angle. Through analyze the difference between the non-paraxial Rayleigh Sommerfeld integral and the paraxial Fraunhofer diffraction integral, we modify the desired output intensity distribution with coordinate transformation and intensity adjustment. Then the paraxial Fraunhofer diffraction integral can be used to design the DOE, which adopts the fast-Fourier-transform (FFT) algorithm to accelerate the computation. To verify our method, the simulation and the experiments are taken. And the result shows that our method can effectively rectify the pillow distortion and can achieve the exact diffraction angle.
In this paper, a novel thin film was proposed for optical super-resolution imaging, which contains a layer of closely-arranged barium titanate glass microsphere with diameter about 30-100μm embedded in a transparent polydimethylsiloxane soft mold. Then the imaging mechanism was analyzed by the finite-difference time-domain (FDTD) simulation and spectrum analysis method. Finally, the thin film was prepared and used to image the sample with sub-wavelength feature to confirm the capability of super-resolution imaging. The experimental result shows that an irresolvable Blu-ray DVD disk with feature size of 300nm can be resolved by placing a thin-film on its surface and then look through it with a conventional microscope. The thin film presented here is flexible, lightweight, easy to carry and can be used in the nanophotonics, nanoplasmonics, and biomedical imaging areas.
This paper presents an approach used to fabricate resonant subwavelength grating based on thiol-ene material. First of all, polydimethylsiloxane soft imprint stamp with opposite structure of the subwavelength grating master mold is made by casting. Then, the desired subwavelength grating with UV-curable thiol-ene material grating structure is fabricated using the polydimethylsioxane soft stamp by UV-curable soft-lithography. Here, we fabricate a subwavelength grating with period of 300nm using the approach, which could reflect blue light with wavelength ranging from 448nm to 482nm at a specific angle and presents the excellent resonant characteristic. The experimental results are consistent with the simulation results, demonstrating that the approach proposed in this paper could effectively fabricate the thiol-ene material resonant subwavelength grating structure. The thiol-ene material is a new green UV-curable polymer material, including a number of advantages such as rapid UV-curing in the natural environment, low-cost, high resolution, and regulative performance characteristic. The fabrication technique in this paper is simple, low-cost, and easy to high throughput, which has broad application prospects in the preparation of micro and nano structures.
KEYWORDS: Microlens array, 3D image processing, Integral imaging, Imaging arrays, Imaging systems, 3D displays, Positron emission tomography, 3D image reconstruction, Lithography, 3D modeling
Integral imaging system with soft substrate is proposed and fabricated by lithographic method. The integral imaging
system consists of microlens array and micro-image array. Based on the optical design theory, the geometrical
parameters of the microlens array and micro-image array is calculated and simulated by the software Tracepro.
Furthermore, some experiments are carried out. The microlens array and micro-image array is fabricated on
Polyethylene Terephthalate substrate by lithographic method. After the alignment between the microlens array and the
micro-image array, three dimensional image can be formed over the microlens array. The imaging system is easy to
curve and can be used on some static displays, such as three dimensional display, three dimensional picture and so on.
The deflection of light of a single optical surface is limited by the Fresnel reflection loss and it is usually not enough to
meet the requirements in large road width, tilt lighting LED lens design. This paper presents a method which greatly
increases the light deflection angle of LED lens by combining a tilting aspherical surface with a freeform surface. Using
this design method, a road lighting LED lens for length L= 30m, road width W=12m and tilt angle θ = 15 ° is designed and manufactured. The experimental results show that the overall road luminance uniformity is as high as 0.7. This design method greatly expand the light distributing capacity of the free-form surface LED lens, and it can be widely used in the design of LED road lighting lens and other illumination applications where large light deflection angle is needed.
In this paper, quite effective method for the design of phase-only and quantized diffractive optical element (DOE) for beam splitting with simulated annealing algorithm (SA) is presented. For this method employs the character that periodic DOE could generate periodic point array, design time and number of sampling point of DOE could be greatly reduced. Besides, the relation of the DOE parameters including the sampling size, number of sampling point and divergence angle are analyzed. The cause and elimination of the high diffraction orders is also investigated. Design result shows that our method is quite effective and can keep the higher diffraction efficiency and lower uniformity error compared to the Gerchberg-Saxton algorithm (GS).
Novel antireflective surfaces with silica particles arranged regularly and tightly are proposed and fabricated by self
assemble silica nanoparticle through electrostatic attraction between charged colloidal particles and charged
polyelectrolyte multilayer. Due to regularly arrangement of the particles, the nanoparticle coatings, as homogeneous
porous layers with uniform distribution, show high-quality and uniform antireflective capability in each region on the
substrate. It has been sufficiently demonstrated in our experiments. Furthermore, the relations among the antireflective
capability, average size of nanoparticles, and incident angle of the irradiated light are calculated by finite-difference
time-domain method. It is demonstrated that the nanostructure coatings with particles of 100 nm size possess the
excellently suitable performance for reflection/transmission with respect to visible-light region. From the results, the
fabricated anti-reflective nanostructures have great potential to improve the efficiency of optoelectronic devices such as a
photo-detector and solar cells.
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