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.
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.
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.
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.
A method of realizing a compact Fourier transform spectrometer is proposed in this work, which is based on the polarization interference in a single layer of birefringent liquid crystal (BLC). The continuous interference between the ordinary light and the extraordinary light is driven by a continuously adjusted electric field. Benefiting from the single-layer configuration with no moving parts, the spectrometer is easily miniaturized. The method to realize the spectrometer is theoretically analyzed and experimentally demonstrated by a layer of nematic BLC with a 100-μm thickness.
Polymer optical elements have widely been investigated because of their low cost and simple fabrication. Currently, UV-curable epoxy resins have been become general polymer materials for optical elements. However, they are still limited by their intrinsic properties, such as a relatively low rate of polymerization and high formulation viscosity. This paper proposed and demonstrated a rapid UV-curable process for polymer optical elements fabrication based on a UV-curable and low-viscosity thiol-ene composition. Several optical elements, including one-dimensional gratings with a 10-um period, Dammann Gratings and microlens arrays (100μm lens diameter), were fabricated by the UV-curable thiol-ene composition and their optical properties were examined in detail.
High performance infrared polarizer with broad band is required for various infrared applications. The conventional infrared polarizer, based on the birefringence effect of natural crystal, is cost-consuming in fabrication and can hardly be integrated into micro-optical systems due to its large bulk. In this paper, an infrared polarizer is proposed in the spectrum from 3 to 19 μm based on sub-wavelength metal wire grid. The dependence of the performance on some key parameters, including metal materials, geometrical parameters, has been deeply investigated by using the Finite-Difference Time-Domain (FDTD) method. The results show that Au wire-grids have a higher transmittance for the Transverse Magnetic(TM) mode light than that of other metal materials, and both the grid period and the grid thickness have important impact on the performance. Based on these observations, a polarizer has been designed by choosing the optimal value of related parameters. Numerical simulation suggests that the designed infrared wire grid polarizer have advantages of broad band, high TM polarization transmission efficiencies and high extinction ratios. The transmission efficiencies of TM polarization are larger than 59.3%, and the extinction ratios range from 28.6 to 44.6 dB in that range of the spectrum.
Biological inspiration has produced some successful solutions for different imaging systems. Inspired by the compound eye of insects, this paper presents some image process techniques used in the spherical compound eye imaging system. By analyzing the relationship between the system with large field of view (FOV) and each lens, an imaging system based on compound eyes has been designed, where 37 lenses pointing in different directions are arranged on a spherical substrate. By researching the relationship between the lens position and the corresponding image geometrical shape to realize a large FOV detection, the image process technique is proposed. To verify the technique, experiments are carried out based on the designed compound eye imaging system. The results show that an image with FOV over 166° can be acquired while keeping excellent image process quality.
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).
With the rapid development of science and technology, optical imaging system has been widely used, and the
performance requirements are getting higher and higher such as lighter weight, smaller size, larger field of view and
more sensitive to the moving targets. With the advantages of large field of view, high agility and multi-channels,
compound eye is more and more concerned by academia and industry. In this work, an artificial spherical compound eye
imaging system is proposed, which is formed by several mini cameras to get a large field of view. By analyzing the
relationship of the view field between every single camera and the whole system, the geometric arrangement of cameras
is studied and the compound eye structure is designed. By using the precision machining technology, the system can be
manufactured. To verify the performance of this system, experiments were carried out, where the compound eye was
formed by seven mini cameras which were placed centripetally along a spherical surface so that each camera points in a
different direction. Pictures taken by these cameras were mosaiced into a complete image with large field of view. The
results of the experiments prove the validity of the design method and the fabrication technology. By increasing the
number of the cameras, larger view field even panoramic imaging can be realized by using this artificial compound eye.
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.
An axicon structured lens is designed and its properties of long focal depth is demonstrated. The phase function of the axicon structured lens is constructed according to the properties of nondiffractive Bessel beam with uniform-intensity. Based on the relationship of the side length of the square hole and the phase retardation, the required phase distribution of the axicon structured lens with a long focal depth in a metallic film can be determined. To verify the feasibility of the method, an axicon structured lens with focal length 1000 mm, a focal depth larger than 20 mm was designed and the intensity distribution of far field was calculated. The results show that the focal depth is 25 mm which is nearly 7 times extended with nearly diffraction-limited image quality.
A frequency tunable electromagnetic metamaterial is proposed based on mechanical movement method. Two rings are
etched against each other on two separate substrates and the two substrates can be adjusted to move relatively. Thus, the
resonant frequency can be modulated due to the changed coupling capacitance between the rings according to equivalent
circuit theory. Simulation results show that the transmissions (S21) can be continuously adjusted, and the retrieved
effective parameters based on simulated scattering parameters reveal that the negative permittivity is available and the
negative permittivity frequency region can be tuned downward or upward by slipping the rings either along or
perpendicular to the gap's directions. By combining frequency modulations in the two directions, resonant frequency can
be shifted from 6.2 GHz to 8.7 GHz, which has realized an efficient modulation in a broad frequency range. The
proposed tunable metamaterial has potential applications to design dual band, multi-band antennas and frequency
reconfigurable antennas.
The detection limit of surface plasmon resonance imaging (SPRI) biosensor is constrained in part by the SPR biochip
and in part by the resolution of the optical intensity of detecting instruments. In this paper, silicon photodiode is
proposed as the optical intensity detecting element instead of the traditionally used charge coupled device (CCD),
combining with high resolution analog/digital converter, this method can efficiently reduce the cost and increase the
sensitivity of the SPRI system while keeping its virtue of multiple channels real time detecting. Based on this method,
An SPRI experimental system with two channels is designed and the optical intensity of each channel is detected by a
photodiode. By carrying out testing experiments using sucrose solution with different concentrations (corresponding to
different refractive index), the system sensitivity of 10-6 refractive index unit (RIU) is obtained.
The correction of the human eye's higher-order wave aberrations by a phase plate has been studied. The phase plate was made by using a single-mask-moving technique. The imaging quality has been analyzed in terms of several metrics. The results show that the fabrication error is 0.05 µm, which is close to /14 at the medium value of the wavelength of white light, and the performance of the eye can be improved by the phase plate, indicating that the single-mask-moving technique has potential applications in clinically correcting ocular aberrations.
Phase modulation characteristics of subwavelength metallic square holes are investigated for 2D imaging purpose. Based
on Maxwell equations, the transmission model of three-dimension subwavelength metallic holes is founded by a mode
expansion technique. The relationship between the widths of the holes and the phase from -π to π is established when the
thickness of metallic film is given. Then the influences of coupling electromagnetic (EM) fields as well as the incident
angle on phase retardation are investigated and calculated through varying the center distance between double holes. A
slab lens is demonstrated by using hole-array formed on a metallic film, which verifies the theoretic analysis.
A biochemistry nanosensor based on hybrid metallic nanostructure array was put forward in this paper. The hybrid
metallic nanostructure array consists of two types Ag nanostuctures, spherical and pyramidal structures with the same
period. A biochemistry sensor experiment is demonstrated by detecting the transmittance spectra of hybrid metallic
nanostructure using Sciencetech spectrophotometer. The wave peaks of transmittance spectra have shifts when the
metallic periods and the refractive index of Ag nanostuctures are different.
A laboratory turbulence simulation based on irregular micro-optical structures has been studied. The phase distributions are derived from Kolmogorov spectra with different Fried parameters r0 by using the fast Fourier transform technique. A mask-shifting method has been invented for generating the designed irregular phase on a quartz substrate. The fabricated element is rotated by a motor to construct a turbulence generator. The dynamic phase produced by the generator is measured in real time with Shack-Hartmann sensor. The resulting power spectrum and the Fried parameter agree with the expected ones. Some issues associated with the simulation of turbulence are discussed.
To collimate effectively the beam emitted from the stacked laser diode in which the lasing surfaces of the diode bars are not located in a plane, a new type of fast-axis collimator, refractive cylindrical microlens array with tunable focal lengths, is presented in this paper. Each lens of the array has the same diameter of 300μm but different focal lengths, ranged from 430μm to 540μm. By means of the mask moving lithography and replication technology, the microlens array was successfully fabricated. The measured fast-axis divergence of the stacked laser diode beam after the collimator was 25mrad, about half of the one (40mrad) for the microlens array with common focal lengths of 400μm.
A profile formation and control approach has been developed for manufacturing micro-optical elements with continuous profile and deep relief depth. Based on Dill's exposure model, an effective expression for determining the exposure dose function is established by using a supposition of equivalent exposure threshold inside a resist layer. An analytical simplified formula is further deduced by taking absorbance as constant B, and the approximate condition is discussed. For evaluating the simplified formula, the profile error was calculated and analyzed by simulation. With the exposure dose function, the binary mask for manipulating the light distribution by means of a moving-mask lithographic method can be designed. Experimental results are given and show the comparative performance to the required profile and relief depth. A series of refractive microlens arrays with aspherical profiles, a wide range of numerical apertures (0.005 to 0.6), and high fill factors were accomplished in the lab and may be applied to many systems.
In order to form the proper aspherical microlens array profile with larger NA on photosensitive materials, a method is developed based on the characteristics of resist and processing parameters during development, for designing the exposure distribution, an experience formula has been proposed in the paper. Using the moving mask method, the exposure energy distribution function related to the photolithographic mask function can be determined by the experience formula. The profile control procedure is formed especially for the deeper relief profiles, after the binary mask data are slightly modified, the micro-structure with aspherical lens profile can be fabricated on the selected thicker resist, the micro relief profile error can be controlled in a certain range. The micro-profile is farther transferred to fused silica by ICP etching system. By our method, the fast microlens array elements with good fidelity and reasonable roughness have been fabricated and applied to the laser diode collimating system.
A new method for microlens profile design was developed based on the analysis to the main parameters of microlens array, including micro profile formation, the numerical aperture ( NA ), the maximum sag depth for the refractive lens and the minimum zones width for the diffractive lens. With the relationships among the parameters, the microlens array in different profile can be determined effectively. The moving mask method[1] is used to realize the required profiles, an unique photolithography system have been built for implementing the mask moving exposure in both X and Y directions for the creation of microlens array. By modifying the binary moving mask, optimizing the photosensitive materials and the processing technique, the microlens profile error can be controlled in the range of 0.4µm~3µm depending on effective reliefdepth of the microlens. In our method, both diffractive and refractive microlens array with larger NA and higher fill factor can be fabricated for satisfying a plenty of purposes.
Performances of diffractive and refractive microlens array have been studied and compared. Besides the diffractive microlens array which can be fabricated by means of the microfabrication technologies, method for manufacturing continuous profile refractive microlens array with larger sag depth has been developed for solving the unique problems like diode laser alignment. Both diffractive and refractive microlens array with different numerical aperture and other parameters are fabricated according to the application requirements, experimental results are given.
In this paper, a method for improving the performance of unit infrared detector has been proposed. An experiment was carried out by putting micro-concentrator in front of the tested detector, micro-concentrators are diffractive microlens with different numerical aperture (N.A.) which were obtained by special design and fabrication. The performance has been evaluated for the coupled detector and compared with the simulation.
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