Image Quality Of Optical System Research Articles

Design method for lens desensitization adapted to refractive index error

The design of optical systems not only considers the imaging performance but also the manufacturing difficulty and feasibility of the system. In practice, errors in the manufacturing process of glass materials and deviations in glass material parameters introduced in complex environments can both lead to degradation in the imaging quality of optical systems. Optical systems that are sensitive to glass material errors face increased manufacturing difficulty and reduced stability. This paper, based on geometrical optics theory, establishes an evaluation function for refractive index error sensitivity and analyzes its relationship with optical parameters and glass materials. It proposes a design method to reduce the refractive index sensitivity of optical systems. Through simulation verification and analysis using examples, the validity of the desensitization design method is confirmed.

Anti-noise computational ghost imaging based on wavelet threshold denoising

Noise can inevitably affect imaging quality of optical imaging system. In this paper, a method of computational ghost imaging (CGI) with better anti-noise performance is proposed by using wavelet threshold denoising (WTD). The simulation and experimental results show that this method exhibits better robustness against both the light source noise and the path noise. To explain this phenomenon, the decline rate of the correlation coefficients between speckle patterns (CCSP) under different noise levels are analyzed. As a post-processing method, our method is simple to implement and is applicable to both random speckle CGI and orthogonal modulated CGI, potentially broadening application prospects in practical applications of ghost imaging.

Lightweight super-resolution multimode fiber imaging with regularized linear regression

Super-resolution multimode fiber imaging provides the means to image samples quickly with compact and flexible setups finding many applications from biology and medicine to material science and nanolithography. Typically, fiber-based imaging systems suffer from low spatial resolution and long measurement times. State-of-the-art computational approaches can achieve fast super-resolution imaging through a multimode fiber probe but currently rely on either per-sample optimised priors or large data sets with subsequent long training and image reconstruction times. This unfortunately hinders any real-time imaging applications. Here we present an ultimately fast non-iterative algorithm for compressive image reconstruction through a multimode fiber. The proposed approach helps to avoid many constraints by determining the prior of the target distribution from a simulated set and solving the under-determined inverse matrix problem with a mathematical closed-form solution. We have demonstrated theoretical and experimental evidence for enhanced image quality and sub-diffraction spatial resolution of the multimode fiber optical system.

Оптическая система для малогабаритного космического аппарата дистанционного зондирования Земли формата CubeSat

The paper considers relevance of creating the small-sized high-resolution optical systems for the small spacecraft. It describes the current state of domestic and foreign systems engaged in the Earth remote sensing of the CubeSat format that confirmed the need to develop domestic multi-component satellite constellations. Unlike the large-sized spacecraft, the CubeSat standard implies introduction of the micro-format satellites. In order to reduce overall dimensions of the system and minimize the chromatic aberrations effect on the image quality in selecting the optical scheme components, mirrors are preferred, as a rule. Among all possible design schemes, the Ritchey --- Chretien optical scheme is the most promising due to its simplicity, small overall dimensions and high optical performance in a wide spectral range for the CubeSat satellites. Main optical and technical parameters, as well as the optical system characteristics for a small spacecraft are provided. For typical systems, the paper proposes a calculation technique; and a simulation model was created making it possible to assess the optical system image quality. The root-mean-square value of the point scatter spot radius in the image plane was taken as the criterion in evaluating the image quality. It is shown that the Ritchey --- Chretien optical scheme and its elements are characterized by its relative easiness in implementation due to using the studied technologies of the lens and mirror elements manufacture and ensuring high image quality and required overall dimensions, which makes it possible to use them in creating a multi-component satellite constellation

Combined finite-element and scalar diffraction simulation of light scattering on zone edges of diffractive intraocular lenses.

A method has been developed to simulate the effects of scattered light on the image quality of optical systems. The coherent model is based on geometrical optics to take account of wavefront aberrations caused by lenses, applies finite-element calculation to solve Maxwell's equations around small scattering structures such as edges of diffractive surface zones, and uses scalar diffraction for free-space light propagation. The implementation is discussed in detail, and the operation is demonstrated on diffractive intraocular lenses. Point spread and modulation transfer functions are evaluated for an axial object point, taking account of scattered light as a function of slant angle and round radius of diffractive zone edges. Results show that, at a distance of ±200 Airy radius (i.e.,±2.1∘) from the axis, scattered irradiance is about 5 times more than without considering edge effects. Optimum round radius was found to be 7% of the step height, which agrees with simple geometrical optical estimations.

Improving the image quality of optical systems with radially symmetrical phase mask

An optical system with a radially symmetrical phase mask allows to extend the depth of field. However, the contrast of the optical system is still lower than that of the diffraction pattern of the traditional optical system. In this paper, we introduce a new method for image enhancement of optical systems with radially symmetric phase masks. The optical system with a traditional radial symmetric phase mask would result in a dot point spread function. The optical system with an improved symmetric phase mask results in a dark center point spread function. The two images that will be obtained correspond to the optical system with two phase masks. On the basis of these two images, a mathematical relationship is proposed in order to obtain good quality images. The simulation results have demonstrated the proposed method to improve the image quality of the optical system with the radial symmetrical phase mask.

Analysis and Prediction of Effect of Turning Marks Diffraction on Image Quality of Optical System

Analysis and Prediction of Effect of Turning Marks Diffraction on Image Quality of Optical System

Fiber bundle optical system: imaging modeling and analysis

The fiber bundle (FB) optical system is widely used in many fields, such as medical imaging and military reconnaissance, owing to its advantages of high design freedom, small volume, and light weight. The traditional theory for the optical transfer function is not suitable for such a discrete sampling optical system. Researchers have developed numerical calculation methods to analyze the imaging quality of the discrete sampling optical system, in which the geometric model needs to be established and the coupling region needs to be determined. We have developed a simple and computationally efficient imaging theory that is suitable for various combinations of FB and CCD detectors. The coupling modulation transfer function (coupling-MTF) of discrete sampling optical systems of square-arrangement fiber bundles (SFBs) and hexagonal-arrangement fiber bundles (HFBs) are analyzed. Simulation results demonstrate that although SFB has a higher coupling-MTF than HFB, the latter is more convenient in coupling alignment operation. Our results have proven the effectiveness and universality of the proposed theory, and it can be used to guide the system design.

Structural Topology Optimization of Reflective Mirror Based on Objective of Wavefront Aberration

Due to the increasing requirements for the imaging quality of optical systems, the design method for optical–mechanical structures has become a research hotspot in recent decades. To improve the imaging performance of the reflective system, it is often necessary to increase the aperture of the mirror. To meet the imaging quality and lightweightedness requirements of the mirror, the topology optimization method aiming at the minimization of wavefront aberration is proposed. The optical–mechanical coupling relationship is established by ray tracing of the deformed mirror surface fitted by orthogonal bases. The topology optimization model is established by the solid isotropic material with penalization model (SIMP). Additionally, the adjoint method is used to analyze the sensitivity of the objective and the constraints. To illustrate the rationality and effectiveness of the method, the mirrors of the Cassegrain system have been optimized under the action of gravity with the objective of the weighted sum of squares of wavefront aberration coefficients under the constraints of the mass of the design domain, the rigid body displacement of the mirror surface, and the residual of deformation fitting. The results show that the proposed method can effectively improve imaging performance under the condition of satisfying the constraints. In addition, the optimization method with wavefront aberration as the objective is a concrete application of the idea of opto-mechanical integration, which can improve optical performance more directly and effectively.

An Inversion Method for Coupled Typical Error Sources based on Remote Sensing Image

According to the error sources and their error amounts obtained by the remote sensing imaging coupled typical error sources inversion method, we can improve the imaging quality of optical systems and make high-quality remote sensing images more useful in military and civilian fields. Based on the distorted remote sensing images, this paper proposes a remote sensing imaging coupled typical error sources inversion method, which can accurately invert the typical error sources of remote sensing imaging and their error amounts. Firstly, a set of coupled typical error decoupled equations are constructed according to the modulation transfer function model of typical error sources and the decoupled principle of the coupled error sources. The initial values of coupled typical error sources are subsequently determined based on the Deep Residual Shrinkage Network (DRSN). Finally, the Levenberg Marquardt-Particle Swarm Optimization (LM-PSO) hybrid optimization algorithm is used to solve the system of coupled typical error decoupled equations to invert the typical error sources and their error amounts of the remote sensing imaging system. The experimental results show that the relative error between the inverse value and the real value of the coupled typical error sources of the distorted remote sensing images by the method in this paper does not exceed 20% at most, and most of them are below 10%, which has excellent inversion performance.

Optical setup for evaluating image quality of thermal imaging lenses working in the spectral region of 8÷12 µm

In this paper, we demonstrate a homemade setup and an image processing algorithm to evaluate the image quality of optical systems working in the spectral region of 8-12 µm. The working principle of our approach relies on measuring the line spread function (LSF) and the modulation transfer function (MTF). All components in the setup are carefully designed and manufactured, and we strictly follow quality control to limit measurement errors. The setup can determine the LSF and MTF of a thermal imaging lens with a focal length of f' ≤ 500 mm and pupil diameter D ≤ 100 mm. A number of objective samples have been studied using our setup, and the experimental results indicate that our setup can work reliably with high accuracy.

Depth-resolved XPS analysis of classically manufactured glass surfaces: suggesting the impact of polishing-induced modifications on the performance of optical systems

During classical polishing, glass surfaces are inevitably chemically modified. Against this background, the composition of conventionally manufactured crown and flint glass surfaces was analyzed via depth-resolved X-ray photoelectron spectroscopy in this work. It is shown that essential glass-forming elements are reduced up to a depth of a few tens of nanometers, depending on the glass type. This indicates the inderdiffsuion of elements between the glass material and the aqueous polishing suspension. Moreover, contaminants from the suspension were detected at the glass surface. The results also suggest a gradient-like growth of a hydrated silica layer. Hence, the index of refraction of the glass surfaces is notably decreased by polishing as verified via ellipsometry. Ray tracing simulations show that this might lead to a decrease in imaging quality of optical systems.

Desensitization Design Method for Freeform TMA Optical Systems Based on Initial Structure Screening

Achieving aberration correction can improve the imaging quality of an optical system, and reducing the error sensitivity of system can improve the realizability of the system. In order to obtain an off-axis three-mirror optical system with high image quality and low error sensitivity, a design method is proposed which obtains the initial structure of the three-mirror anastigmatic (TMA) optical system with low error sensitivity through a nondominated sorting genetic algorithm II (NSGA-II). Combining the comprehensive evaluation function of image quality and error sensitivity, this method iteratively selects multiple freeform surface types to determine the combination with the lowest error sensitivity and obtains the freeform TMA optical system with optimal overall performance. A freeform TMA optical system is designed by the method proposed in this paper, and the error sensitivity of the optical system is analyzed. The results show that the image quality of the freeform optical system is effectively improved and the error sensitivity is effectively reduced with the same error applied, which verifies the correctness and practicality of the method.

Computational Imaging in Dual-Band Infrared Hybrid Optical System with Wide Temperature Range.

The special dispersion and temperature characteristics of diffractive optical element (DOE) make them widely used in optical systems that require both athermalization and achromatic aberrations designs. The multi-layer DOE (MLDOE) can improve the diffraction efficiency of the overall broad waveband, but its diffraction efficiency decreases with changes in ambient temperature. When the ambient temperature changes, the micro-structure heights of MLDOE and the refractive index of the substrate materials change, ultimately affecting its diffraction efficiency, and, further, the optical transform function (OTF). In this paper, the influence of ambient temperature on the diffraction efficiency of MLDOE in a dual-infrared waveband is proposed and discussed, the diffraction efficiency of MLDOE caused by ambient temperature is derived, and a computational imaging method that combines optical design and image restoration is proposed. Finally, a dual-infrared waveband infrared optical system with athermalization and achromatic aberrations corrected based on computational imaging method is designed. Results show that this method can effectively reduce the diffraction efficiency of MLDOE by ambient temperature and improve the imaging quality of hybrid optical systems.

Two-component compensators of field aberrations of optical systems

Subject of study. Two-component optical schemes of compensators of field aberrations of optical systems calculated based on the third-order aberration theory and modular method of optical system design [Izv. Vyssh. Uchebn. Zaved., Priborostr.57, 57 (2014)] are proposed. These compensators enable correction of two aberrations: Petzval field curvature and astigmatism or longitudinal chromatic aberration and lateral color or transverse chromatic aberration. Method. A modular method for the design of optical systems based on the third-order aberration theory was used in the calculation. This method consists of synthesis of the systems using optical elements (modules) with known correcting properties [Izv. Vyssh. Uchebn. Zaved., Priborostr.57, 57 (2014)]. Aplanatic menisci with different linear magnifications and a hyperchromatic lens were used as optical modules. The aplanatic menisci were used to calculate the compensator of Petzval field curvature and astigmatism, whereas the hyperchromatic lens was used to calculate the compensator of longitudinal and transverse chromatic aberrations. Main results. The use of two-component compensators of field aberrations enables significant enhancements in the aberrational properties of the objectives, improves the image quality of optical systems, and increases their optical parameters, particularly the angular field of doublet objectives (fivefold) using the correcting properties of optical modules (menisci and hyperchromatic lens). Practical significance. The introduction of a compensator composed of two aplanatic menisci positioned at a significant distance from each other into the optical system makes it possible to correct such aberrations as field curvature and astigmatism regardless of the number of lenses in the objective and increase the angular field. The introduction of a compensator of chromatic aberrations into an optical scheme of a high-aperture microscope objective with 100×1.25 oil immersion corrects the longitudinal and transverse chromatic aberrations. This makes it possible to cease the use of compensating eyepieces with a complex optical scheme and replace them with standard eyepieces as well as to use a microscope where the optical radiation is detected by a charge-coupled device array or complementary metal oxide semiconductor detector instead of the human eye.

Research on the Coupled Modulation Transfer Function of the Discrete Sampling System with Hexagonal Fiber-Optic Imaging Bundles

In this study, we developed a numerical model of the coupled modulation transfer function (coupled-MTF) based on the discrete sampling system from the perspective of optical system imaging quality evaluation for coupled two-dimensional discrete sampling characteristics of the hexagonally aligned fiber-optic imaging bundles and CCD image elements. The results show that when the spatial frequency of the input target signal deviates from the Nyquist frequency by 1%, an increase in the number of fibers leads to a faster convergence of the oscillation of the coupled-MTF, and the coupled-MTF converges to a stable value when the number of fibers reaches 1000 × 1000. The deviation of the spatial frequency of the input target signal from the Nyquist frequency is within 1%, and the oscillatory convergence of the coupled-MTF accelerates with increasing deviation. The coupled-MTF oscillates with the deviation period of the wave peak of the input target signal from the initial position of the fiber center, and the theoretical oscillation spatial period is twice the fiber diameter. This study produces important guidelines for the selection of the number of fibers, input spatial frequency, and initial position deviation of the hexagonally arranged fiber imaging bundles.

The Effect of Temperature and Salinity on Imaging Quality of Optical System in Underwater Turbulence

The Effect of Temperature and Salinity on Imaging Quality of Optical System in Underwater Turbulence

Optimal design of multilayer diffractive optical element in wide angle of incidence

We propose a method for designing the multilayer diffractive optical elements (MLDOEs) to improve the polychromatic integral diffraction efficiency (PIDE) in wide angle of incidence. By comparing and analyzing the characteristic angle weighted PIDE (CAW-PIDE) in the whole angles of incidence, the optimal microstructure height combination of the MLDOE can be obtained. The optimization process and simulation examples for the single-band and multi-band MLDOE are given. Compared to the conventional method, the PIDE is obviously improved in wide angle of incidence by our method. This optimization method can be applied to different working wavebands, and the image quality of the hybrid optical system with the MLDOE can be improved in wide angle of incidence.

RestoreNet-Plus: Image restoration via deep learning in optical synthetic aperture imaging system

The synthetic aperture technology can improve the resolution effectively in the optical imaging system. In fact, the imaging blur, turbulence aberration and noise can affect the imaging quality of optical synthetic aperture imaging system seriously. Several non-blind methods are applied generally to recover the degraded maps with the prior information. However, the restoration effect is not stable enough and satisfactory. As a data-driven approach, the deep learning framework possesses advantages in solving this problem. In this paper we propose an improved network, RestoreNet-Plus, for the image restoration of optical synthetic aperture imaging system. After the proofs of numerical simulation and experiment results, RestoreNet-Plus is a better alternative compared with other methods, owing to its better restoration ability, strong denoising ability and capacity for turbulence correction error.

Freeform imaging systems: Fermat\u2019s principle unlocks \u201cfirst time right\u201d design

For more than 150 years, scientists have advanced aberration theory to describe, analyze and eliminate imperfections that disturb the imaging quality of optical components and systems. Simultaneously, they have developed optical design methods for and manufacturing techniques of imaging systems with ever-increasing complexity and performance up to the point where they are now including optical elements that are unrestricted in their surface shape. These so-called optical freeform elements offer degrees of freedom that can greatly extend the functionalities and further boost the specifications of state-of-the-art imaging systems. However, the drastically increased number of surface coefficients of these freeform surfaces poses severe challenges for the optical design process, such that the deployment of freeform optics remained limited until today. In this paper, we present a deterministic direct optical design method for freeform imaging systems based on differential equations derived from Fermat’s principle and solved using power series. The method allows calculating the optical surface coefficients that ensure minimal image blurring for each individual order of aberrations. We demonstrate the systematic, deterministic, scalable, and holistic character of our method with catoptric and catadioptric design examples. As such we introduce a disruptive methodology to design optical imaging systems from scratch, we largely reduce the “trial-and-error” approach in present-day optical design, and we pave the way to a fast-track uptake of freeform elements to create the next-generation high-end optics. We include a user application that allows users to experience this unique design method hands-on.