Resolution Of Optical System Research Articles

Advantages of Direct Laser Writing for Enhancing the Resolution of Diffractive Optical Element Fabrication Processes

A technology for direct laser writing of code sequences on modulation disks has been developed and implemented, ensuring high accuracy and reliability in the process of forming structural elements. The main advantages of applying direct laser writing compared to contact lithography for forming submicron-sized elements have been demonstrated. The proposed technology is characterized by high resolution and flexibility in configuring the parameters of the optical recording system, making it suitable for a wide range of applications in micro-optics. Direct optical writing is presented as a promising approach for enhancing the resolution of optical systems used in recording submicron-sized diffractive optical elements, as this technology enables the creation of complex optical structures. Additionally, a detailed classification of current approaches for further increasing the resolution of the optical recording system was conducted, including the application of a saturated absorber layer on the photosensitive surface, the use of a laser beam with intensity modeled by a Bessel function, and the synthesis of photosensitive materials with optimized exposure characteristics, ensuring high efficiency and accuracy in the process of direct laser writing.

Synthetic aperture optical image restoration based on multi-scale feature enhancement

With the wide applications of high-resolution imaging technology in topographic mapping, astronomical observation, and military reconnaissance and other fields, the requirements for imaging resolution of optical system are becoming higher and higher . According to the diffraction limit and Rayleigh criterion, the imaging resolution of the optical system is proportional to the size of the aperture of the system, but affected by the material and the processing of the optical component: the single aperture of the optical system cannot be infinitely enlarged. Therefore the synthetic aperture technology is proposed to replace the single large aperture optical system. Owing to the effect of sub-aperture arrangement and light scattering, the imaging of synthetic aperture optical system will be degraded because of insufficient light area and phase distortion. The traditional imaging restoration algorithm of synthetic aperture optical system is sensitive to noise, overly relies on degraded model, requires a lot of manually designed models, and has poor adaptability. To solve this problem, a multi-scale feature enhancement method of restoring the synthetic aperture optical image is proposed in this work. U-Net is used to obtain multi-scale feature, and self-attention in mixed domain is used to improve the ability of of the network to extract the features in space and channel. Multi-scale feature fusion module and feature enhancement module are constructed to fuse the information between features on different scales. The information interaction mode of the codec layer is optimized, the attention of the whole network to the real structure of the original image is enhanced, and the artifact interference caused by ringing is avoided in the process of restoration. The final experimental results are 1.51%, 4.42% and 5.22% higher than those from the advanced deep learning algorithms in the evaluation indexes of peak signal-to-noise ratio, structural similarity and perceived similarity, respectively. In addition, the method presented in this work has a good restoration effect on the degraded images to different degrees of synthetic aperture, and can effectively restore the degraded images and the images with abnormal light, so as to solve the problem of imaging degradation of synthetic aperture optical system. The feasibility of deep learning method in synthetic aperture optical image restoration is proved.

Full-angle high-reflection ultrathin composite film realizing high spatial resolution of scintillation crystal array

The performance of current nuclear medicine imaging systems is largely limited by the performance of detectors, and high spatial resolution detectors require high optical yield scintillator arrays. In this work, we simulated and designed for the first time a distributed Bragg reflector (multilayer dielectric film) that covers the entire lutetium yttrium oxyorthosilicate emission spectral band and consists of three 1/4 wavelength (λ/4) primary film systems centered at 420, 500, and 575 nm. In order to achieve ultrahigh reflectivity at the full incidence angle of the scintillator emitting surface, we propose a master optical configuration combining the dielectric film with a metal film/diffuse reflection adhesive. To explain this mechanism, we also simulated the change in reflectivity of the actual inner surface light collection. Experimental results show that a combination of a highly reflective reflector can achieve full-angle high reflectance at the total angle of incidence. We find that the dielectric film does not change the total reflection structure inside the crystal, while the light-blocking layer changes and increases the angular reflection of the dielectric film about the angle. These findings provide important insights into surface treatment as well as the design of scintillation crystal arrays, with far-reaching implications for high spatial resolution optical imaging systems.

Depth-dependent dispersion compensation for the micron resolution optical coherence tomography with a time-frequency analysis method

In the noninvasive imaging of the samples such as biological tissues with various forms of OCT, the dispersion effect would seriously influence the image contrast and resolution. Compared with the invariant dispersion, the sample-induced dispersion is much more difficult to be compensated because it is depth-dependent. In this work, we proposed a time-frequency analysis method to compensate for the depth-dependent dispersion without the pre-knowledge of the dispersive property of the tissue. With the Radon-Ambiguity transform and the fractional Fourier transform the dispersion amount corresponding to the specific depth could be calculated and compensated. The validity of this algorithm was first demonstrated by the simulation of the compensation of the water-induced dispersion at the micron resolution. Furthermore, the TiO2 phantoms and the fingertip of a healthy human volunteer were measured with the common-path micron resolution optical coherence tomography system. The experimental results revealed that the image resolution acquired by the method proposed could be improved by a factor of 2–3. This work can be helpful for dispersion compensation in other optical fields.

Impact of Optical System Resolution on Digital Image Correlation Measurement Results

Impact of Optical System Resolution on Digital Image Correlation Measurement Results

Polarization-conversion microscopy for imaging the vectorial polarization distribution in focused light

Polarization is a significant factor in a great variety of optical phenomena, playing an important role in determining the focusing properties of lenses, in the resolution of optical systems, and in the performance during laser processing. Knowing the polarization distribution in focused light is critical to understanding and designing relevant optical devices and systems. However, it remains challenging to characterize the vectorial polarization distribution in optical fields. We develop a polarization-conversion-based optical microscope for directly acquiring the distribution of three orthogonal polarizations in focused light and theoretically prove and experimentally demonstrate its validity by characterizing super-resolution focused light with different incident polarizations.

Design and analysis of segmented-mirror primary mirror system

with the development of space exploration, the resolution of optical system is required to be higher and higher. According to the Rayleigh criterion, the resolution of the optical system is directly proportional to the aperture. However, due to the influence of processing capacity and size of the rocket fairing, it is difficult to achieve one single large aperture. Therefore, the scheme of using small size segmented-mirror to achieve one large aperture becomes an effective form. Because location difference between the deployment and the ideal position, the imaging quality will be affected, and cannot be imaged in serious case. For the analysis of influence of the position error on the imaging quality, the traditional method is to analyze on the optical transfer function and Strehl ratio in theory, ignoring the influence of various aberrations that cannot be corrected by the optical system itself. In this paper, the segmented-mirror primary mirror system model is established to analyze the influence of the position error and the real influence of the various aberrations of the system, so as to complete the analysis of the influence more comprehensively. Through the analysis of different position errors, we can get the final wave-front aberration and Strehl ratio of the system under the influence of position error, which can be used as a reference for the analysis of position error influence of segmented-mirror primary mirror form and sparse aperture form of large aperture optical system in the future.

Transient dynamical-thermal-optical system modeling and simulation

In modern high resolution optical systems like astronomical telescopes or lithographic objectives, performance degradations can be caused by various disturbances. Holistic optical system simulation is required to predict the performance or the high precision systems. In this paper a method for transient dynamical-thermal-optical system modeling and simulation is introduced. Thereby, elastic deformation, rigid body motion, and mechanical stresses due to dynamical excitation are calculated using elastic multibody system simulation and temperature changes are determined using thermal finite element analysis. The deformation, the motion, and the mechanically and thermally induced stress index changes are then considered in a gradient-index ray tracing. Finally, the presented method is applied in a dynamical-thermal single lens system.

Optimization of Thickness Uniformity Distribution on a Large-Aperture Concave Reflective Mirror and Shadow Mask Design in a Planetary Rotation System

Improving the spatial resolution of remote sensing satellites has long been a challenge in the field of optical designing. Although the use of large-aperture reflective mirrors significantly improves the resolution of optical systems, controlling the film thickness uniformity remains an issue. The planetary rotation system (PRS) has received significant attention owing to the excellent uniformity of the coating applied to the large-aperture reflective mirror. However, the development of the PRS remains hindered by a lack of research on its properties and the design method of the shadow mask. To address this, we performed a theoretical analysis of the distribution of film thickness and uniformity in the PRS, which is impacted by parameters of geometric configuration in the vacuum chamber. We present a film thickness expression based on Knudsen’s law and the geometric configuration of the vacuum chamber that incorporates an additional shading function. Moreover, the variation of uniformity in the standard and counter PRSs was elucidated by changing the location of the evaporation source. Finally, a fixed-position shadow mask, which was obtained by theoretical design, allows the nonuniformity of the concave reflective mirror (with a 700 mm aperture) to reduce from 2.43% to 0.7%, highlighting the importance of initial shape design.

Optical design of InGaN/GaN nanoLED arrays on a chip: toward: highly resolved illumination

The physical laws of diffraction limit the spatial resolution of optical systems. In contrary to most superresolution microscopy approaches used today, in our novel idea we are aiming to overcome this limit by developing a spatially resolved illumination source based on semiconductor nanoscale light emitting diode (nanoLED) arrays with individual pixel control. We present and discuss the results of optical simulations performed for such nanoLED emitter arrays and analyze the theoretical limits of this approach. As possible designs we study arrays of GaN nanofins and nanorods (obtained by etching nanofin arrays), with InGaN/GaN multi quantum wells embedded as active regions. We find that a suitable choice of the array dimensions leads to a reasonably directed light output and concentration of the optical power in the near field around an activated pixel. As a consequence, the spatial resolution for this type of microscopy should only be limited by the pixel pitch, and no longer by the optical diffraction. Realization of optimized nanoLED arrays has a potential to open new field of chip based superresolution microscopy, making super-high spatial resolution ubiquitously available.

Direct measurements of the properties of Thick-GEM reflective photocathodes

In the context of the development of novel Thick GEM based detectors of single photons, the high spatial resolution optical system, nicknamed Leopard, providing a detailed surface scanning of these electron multipliers, has been used for a set of systematic measurements of their key properties. In particular, gain uniformity and photoelectron extraction dependence on geometry and electric field configuration have been studied. These results are reported and discussed. They improve the understanding of the Thick GEM properties by novel measurements and confirmation of previous indirect measurements and they answer to relevant questions related to their use as photocathode substrates in novel gaseous photon detectors.

The optimal design of a binaural sparse-aperture system

Optical sparse-aperture (OSA) can greatly improve the spatial resolution of optical system. However, its optical designs are complex. This paper proposes a binaural sparse-aperture system with a simple and symmetrical structure, which is composed of three apertures. Apertures are rotated to obtain rich frequency information. The scheme of rotating apertures is analyzed by taking the ratios of sub-apertures and the number of rotations as variables. The image artifacts are suppressed through processing in the frequency domain. Simulation results analyze the effects on OTFs and imaging quality with different rotation numbers and ratios of sub-apertures. Experimental results show that this system can reach almost the same cut-off frequency as what the equivalent multi-aperture system can reach.

The effect of preservative free hydrocortisone 0.335% eye drops on tear film thickness in patients with moderate to severe dry eye disease

AbstractPurposeDry Eye Disease (DED) has been found to be associated with reduced pre‐corneal tear film thickness (TFT). Previous studies have shown that topical lubricants have the potential to increase TFT in patients with DED. In the present study, we investigated whether anti‐inflammatory therapy with topical low dose preservative free (PF) soft steroid, hydrocortisone 0.335% eye drops also has an effect on TFT in patients with moderate to severe DED.MethodsA total of 60 patients with moderate to severe DED were included. Patients were randomized to receive either hydrocortisone 0.335% for 12 days 4 times daily followed by 2 days twice daily instillation (intense treatment group) or 8 days 3 times daily followed by 3 days twice daily treatment (recommended treatment group). TFT was assessed using a custom‐built ultra‐high resolution optical coherence tomography system at baseline, at day 14 and day 28. Measurement of intraocular pressure (IOP) and standard clinical tests to assess signs and symptoms of DED, such as the Ocular Surface Disease Index (OSDI), were performed.ResultsFour weeks after treatment start, a significant increase in TFT was observed in both groups (5.3 ± 8.9%, p = 0.03 vs. baseline in the intense and 5.6 ± 13.1%, p = 0.04 vs. baseline in the recommended treatment group) with no difference between the two groups (p = 0.94). IOP did not change at the end of the treatment period in neither of the two treatment groups (p = 0.38, from 14.1 ± 1.8 to 13.9 ± 2.0 mmHg in the intense and from 12.8 ± 1.9 to 13.3 ± 2.1 mmHg in the standard treatment group). OSDI significantly decreased from baseline during the study period in both study groups (p < 0.001, by 19.5 ± 39.1% and 24.1 ± 33.9%, respectively) after PF hydrocortisone treatment.ConclusionsThe present data show that low dose hydrocortisone PF eye drops have the potential to restore TFT in patients with moderate to severe DED. This indicates that this anti‐inflammatory therapy option acts directly in the disease process.

The resolution of optical image edge detection based on Brewster effect

In the present work, we study the influence of the Brewster effect on the resolution of optical system for optical edge detection. The estimation of resolution for initial and transformed images of optical objects is performed both theoretically and experimentally. Our research demonstrates that the image edge detection based on the transformation by the Brewster effect improves the resolution of the optical system approximately by the factor of 1.6.

Optical phase retrieval with the image of intensity in the focal plane based on the convolutional neural networks

One of the most important factors for improving the resolution of optical systems is to compensate for the aberrations (distortions) of the wave front. As a rule, whether special measuring devices (wavefront sensors) are used for such compensation or adaptive mirrors that perform iterative correction of the wavefront. However, often (for reasons of compactness or weight reduction), it is not possible to use the special equipment for measuring aberrations. To obtain certain information on the wave front, one can use the measured point spread function (PSF) or the intensity pattern in the focal plane. Methods of processing two PSFs (focal and nonfocal) with the help of neural networks are known. In this paper, we investigate the possibility of recognizing the wave front from a single intensity pattern in the focal plane. The technology of deep machine learning - convolutional neural network is chosen as the way for implementation. The idea of this technology lies in the alternation of convolutional and subsampling layers, for the purpose of efficient image recognition. Such approach will allow to optimize the process of compensation of optical system aberrations and to reduce the amount of required input data.

Analysis of the possibility of upscaling based on apodization for partially coherent optical systems in the presence of aberrations

The degree of coherence of radiation is an important characteristic on which the interference properties of light fields and, as a consequence, the resolution of optical systems depend. When propagating over long distances even in free space, initially completely coherent or incoherent radiation becomes partially coherent. This fact should be taken into account in the formation of optical images along with the influence of wave front aberrations. In this paper, we investigate the change in the resolution of the system for two near-point light sources depending on the degree of spatial coherence in the presence of different aberrations. The possibility of improving the resolution in the considered situations on the basis of the amplitude apodization of the optical system is also investigated.

High spatial resolution cold neutron imaging with new Tb3+/Ce3+ co-doped Gd2O3 scintillation glass fiber arrays

Abstract The fiber-array-structured scintillation detectors can achieve both high detection efficiency and high spatial resolution for cold neutron radiography. Three novel Tb 3 + /Ce 3 + co-doped Gd 2 O 3 scintillation glass fiber arrays with different thicknesses (0.3 , 0.4 , 0.5 mm) have been fabricated and tested. These arrays were composed of 10 µm diameter Tb 3 + /Ce 3 + co-doped Gd 2 O 3 glass fibers, cladding glass, and extra-mural absorption (EMA) glass. The spatial resolution and the cold neutron absorption efficiency of the imaging system made of 0.4 mm thick fiber array and an optical readout system were measured to be 10 lp/mm (line pairs per millimeter) and 93.4 % for cold neutrons, respectively. The optical readout system consists of a cooled Andor iKon-LDZ936 charge-coupled device, a mirror, and a Nikon Nikkor 135 mm lens. The spatial resolution of the cold neutron imaging system is mainly limited by the low resolution of the optical readout system. To further characterize the spatial resolution of these arrays, a higher resolution optical readout system is desired.

Probing polaritons in the mid- to far-infrared

The long free-space wavelengths associated with the mid- to far-infrared spectral range impose significant limitations on the form factor of associated optic and electro-optic components. Specifically, current commercial optical sources, waveguides, optical components (lenses and waveplates), and detector elements are larger than the corresponding diffraction limit, resulting in reduced image resolution and bulky optical systems, with deleterious effects for a number of imaging and sensing applications of interest to commercial, medical, and defense related arenas. The field of nanophotonics, where the ultimate objective is to confine and manipulate light at deeply subwavelength, nanometer length scales, offers significant opportunities to overcome these limitations. The demonstration of nanoscale optics in the infrared can be achieved by leveraging polaritons, quasiparticles comprised of oscillating charges within a material coupled to electromagnetic excitations. However, the predominant polaritonic materials and the characterization techniques and methods implemented for measuring these quasiparticles in the mid- to far-IR require a different approach with respect to similar efforts in the ultraviolet, visible, and near-IR. The purpose of this tutorial is to offer an overview of the basic materials, tools, and techniques for exciting, manipulating, and probing polaritons in the mid- to far-infrared wavelength range, providing a general guide to subwavelength and nanoscale optics for those entering this exciting and burgeoning research field.

Simulation of detecting piston error between segmented mirrors by Fizaeu interference technique on ZEMAX

The main method to improve the resolution of optical system is enlarging the pupil of optical system, and by using several segmented mirrors to get an equivalent large diameter primary mirror is a common way. After the deployment on orbit, there will be deviation between deployment position and the designed position, which is position error. The error determines the imaging quality of the optical system. So the precision of the position of segmented mirror is needed to be analyzed to make sure the error will not destroy the image quality. This paper uses Fizaeu interference technique to detect the piston error between segmented mirrors, and analyses the detect theory of it. Build model in the ZEMAX and simulate the change of stripe’s position and brightness information. In the end, we get the same result of MATLAB, which testifies Fizaeu is of feasibility to detect the piston error.

Imaging performance of fractal structuresparse aperture arrays

The angular resolution of optical system is limited by the ratio of the wavelength to the aperture of the entrance pupil, indicating that the optical system with large aperture has a high spatial resolution. Sparse aperture imaging is one of the effective solutions to the problem that the telescope is bulky, heavy and difficult to manufacture. According to the self-similarity and multi-scale characteristics of fractal configuration, we propose a sparse aperture array and analyze its performance for synthetic aperture imaging system. In the array Golay-3 is used as a structural unit to expand a multi-layered fractal configuration in a self-similar manner. Given the analytical expression of the pupil function which is reduced by dimensionless parameters, we calculate the modulation transfer functions (MTFs), the practical cut-off frequencies and the middle spatial frequency characteristics of the fractal configuration under different fill factors and different outer layer rotational angles. We analyze both the MTF values and the performance parameters of the fractal structure for the cases of <i>N</i> = 3, 9, and 18, respectively. The results show that the decrease of fill factor does not significantly change the MTF curve nor the practical cutoff frequency in a range of fill factor between 0.0952 and 0.2246. The outer layer rotational angle has a periodicity, and the change in the angle has no large influence on the practical cutoff frequency. When the reduced aperture parameter is <inline-formula><tex-math id="M3">\begin{document}$ {d_0} = 1$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20190818_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20190818_M3.png"/></alternatives></inline-formula> and the fill factor is 22.46%, the middle spatial frequency of <i>N</i> = 18 array is more stable and the practical cut-off frequency is higher. Using the fractal self-similarity, the aperture of the system can be expanded effectively while maintaining the middle spatial frequency characteristics. The computing results are of scale invariance due to the adoption of the reduced aperture parameter.