Annular Lens Research Articles

Sustained release of proteins from contact lenses with porous annulus.

Ophthalmic drugs are administered to the front of the eye by eyedrops. The bioavailability of drugs delivered via eye drops is low due to tear turnover. Contact lenses can address some deficiencies of eye drops by sustaining the delivery of drugs, but commercial contact lenses have small pore sizes that cannot load biologics, which are becoming more common for treating ophthalmic diseases. This study aims to investigate novel poly(hydroxyethyl methacrylate) (pHEMA) lenses with transparent center and porous annulus for sustained release of model proteins. A novel hydrogel polymerization process was used to fabricate concentric, porous layer pHEMA hydrogel rods. The hydrogels were lathe cut into contact lenses which were explored for the delivery of proteins and gold nanoparticles. Lenses were characterized by partition coefficient and diffusivity, which was estimated by fitting experimental data to an analytical model. Transmittance measurements were made to compare transparency of porous lens centers to commercial contact lenses. Porous pHEMA lenses consisting of a concentric, porous layer made from 55% water content in precursor were successfully lathe cut into lenses with transparent center and opaque porous annulus. The porous lenses could load large model proteins of bovine serum albumin and human γ-globulin and provide sustained release. The core annular pHEMA contact lenses consisting of an outer annulus of opaque, porous pHEMA and an inner, center layer of clear, nonporous pHEMA can provide sustained delivery of biologics.

Mathematical modeling and implementation of a panoramic zoom system without central blind area

The panoramic annular lens (PAL) is renowned for providing simultaneous vision of the panoramic space. However, its inherent central blind area is a significant drawback. In this study, we aim to harness the benefits of the PAL while mitigating its limitations by proposing a dual-channel panoramic zoom system without a central blind area. The introduction of a positive front lens group for secondary imaging is a critical aspect of our design, which is guided and substantiated by our mathematical imaging model. The results from our design affirm the practicality and effectiveness of the secondary imaging. This design can achieve a zoom ratio of 1.46× and a maximum field of view (FoV) range of 71°∼100°, enabling zooming from front to rear. Exemplifying compactness, our system measures just 60mm in total length, while providing a high-resolution output, as indicated by a modulation transfer function exceeding 0.3 at 200lp/mm. With an F−θ distortion of less than 3.3%, the system maintains low levels of distortion. The analysis is instructive and the design shows potential in situations that necessitate compliance with size and resolution requirements.

Real-time ghost image characterization for panoramic annular lenses.

As a common but troublesome branch of stray light, ghost images in catadioptric optical systems greatly limit the performances of such optics, including panoramic annular lenses (PAL). A versatile and robust real-time characterization algorithm for ghost images in PAL systems is proposed, with a new ray behavior quantifying index. It characterizes any kind of ghost image in the catadioptric unit with a high reliability, regardless of the actual existence of the ghost images. With newly extracted common feature and properly designed numerical methods specified to PAL systems locating representative rays, the evaluation runs almost instantly, allowing itself to be implemented in optical design process to perform real-time analyses on and to suppress ghost images. Multiple examples show the ability of the method on analyzing ghost image behaviors and achieving ghost-image-suppressed PAL designs. Along with further discussions, the potential of extending the method and its possible wider prospects can be reflected.

Extended-depth-of-field imaging with an ultra-thin folded lens

Optical systems with extended depth of field (EDOF) are crucial for observation and measurement applications, where achieving compactness and a substantial depth of field (DOF) presents a considerable challenge with conventional optical elements. In this paper, we propose an innovative solution for the miniaturization of EDOF imaging systems by introducing an ultra-thin annular folded lens (AFL). To validate the practical feasibility of the theory, we design an annular four-folded lens with an effective focal length of 80.91 mm and a total thickness of only 8.50 mm. Simulation results show that the proposed folded lens has a DOF of 380.55 m. We further developed an AFL-based test system exhibiting a resolution of 0.11 mrad across a wide wavelength range of 486–656 nm. Additionally, we present experimental results from a miniature compact prototype, which further highlights the promising potential of folded lenses for long-range EDOF imaging.

Design, analysis, and manufacturing of a glass-plastic hybrid minimalist aspheric panoramic annular lens

We propose a high-performance glass-plastic hybrid minimalist aspheric panoramic annular lens (ASPAL) to solve several major limitations of the traditional panoramic annular lens (PAL), such as large size, high weight, and complex system. The field of view (FoV) of the ASPAL is 360° × (35° ∼ 110°) and the imaging quality is close to the diffraction limit. This large FoV ASPAL is composed of only 4 lenses. Moreover, we establish a physical structure model of PAL using the ray tracing method and study the influence of its physical parameters on compactness ratio. In addition, for the evaluation of local tolerances of annular surfaces, we propose a tolerance analysis method suitable for ASPAL. This analytical method can effectively analyze surface irregularities on annular surfaces and provide clear guidance on manufacturing tolerances for ASPAL. Benefiting from high-precision glass molding and injection molding aspheric lens manufacturing techniques, we finally manufactured 20 ASPALs in small batches. The weight of an ASPAL prototype is only 8.5 g. Our framework provides promising insights for the application of panoramic systems in space and weight-constrained environmental sensing scenarios such as intelligent security, micro-UAVs, and micro-robots.

PAL-SLAM2: Visual and visual–inertial monocular SLAM for panoramic annular lens

This paper presents PAL-SLAM2, a visual and visual–inertial monocular simultaneous localization and mapping (SLAM) system for a panoramic annular lens (PAL) with an ultra-hemispherical field of view (FoV), overcoming the limitations of traditional frameworks in handling fast turns, nighttime conditions and rapid lighting changes. The system incorporates modules for initialization, tracking, local mapping, loop and map merging. To fully exploit information from the negative space (z<0), keypoints are projected onto the unit sphere for visual initialization and tightly-coupled visual–inertial optimization. Leveraging a multimap strategy, the feature-based PAL-SLAM2 is capable of detecting unidirectional and bidirectional public areas using PAL images, thereby enhancing the performance of loop correction and map merging. Testing indicates that it achieves an average accuracy of 7.1 cm on the PALVIO indoor dataset, surpassing similar state-of-the-art frameworks. Furthermore, we have collected a large-scale dataset comprising over 120,000 images with corresponding inertial measurement unit (IMU) data, demonstrating PAL-SLAM2’s robustness under challenging outdoor conditions. Relying solely on visual and inertial inputs, our system is particularly suited for environments where Global Navigation Satellite System (GNSS) signals are frequently obstructed, such as indoor spaces or dense urban areas. The dataset can be accessed at: https://github.com/wwendy233/Plaza-Dataset.

A high resolution prism-grating panoramic imaging spectrometer based on occultation observations

Occultation observation is an important technique for shadow region detection and a significant complement to the illuminated region detection method. This technology will significantly reduce the impact of background light pollution and provide clearer occultation signals. In order to achieve high-resolution all-round detection in the shadow region, this paper introduces a proposal for a prism-grating panoramic imaging spectrometer based on occultation observations. It utilizes a panoramic annular lens to enable 360-degree occultation observations within the shadow region, combines a grating for spectral separation to obtain spectral information, and achieves an overall straight-line design for the system by adjusting the prism-grating surface's deflection angle. This paper, by analyzing the non-uniformity of light rays from different fields of view after dispersion by the grating, obtains the coordinate information of the spectrum on the image plane, significantly improving the accuracy of subsequent spectral calibration. The design results indicate that the optical system of this imaging spectrometer achieves a spectral resolution of 0.67 nm in the wavelength range of 365–770 nm. At a Nyquist frequency of 37.04lp/mm, the MTF across the entire bandwidth exceeds 0.6. The RMS of the point spread function is less than 9 μm across the full field of view, and aberration correction is excellent. This imaging spectrometer utilizes stellar occultations to achieve real-time 360-degree observations in the shadow region, and at the same time obtains total information on atmospheric components and contour information that varies with occultation height. This scheme offers a more comprehensive information for scientists in related fields.

Minimalist and High-Quality Panoramic Imaging With PSF-Aware Transformers.

High-quality panoramic images with a Field of View (FoV) of 360° are essential for contemporary panoramic computer vision tasks. However, conventional imaging systems come with sophisticated lens designs and heavy optical components. This disqualifies their usage in many mobile and wearable applications where thin and portable, minimalist imaging systems are desired. In this paper, we propose a Panoramic Computational Imaging Engine (PCIE) to achieve minimalist and high-quality panoramic imaging. With less than three spherical lenses, a Minimalist Panoramic Imaging Prototype (MPIP) is constructed based on the design of the Panoramic Annular Lens (PAL), but with low-quality imaging results due to aberrations and small image plane size. We propose two pipelines, i.e. Aberration Correction (AC) and Super-Resolution and Aberration Correction (SR&AC), to solve the image quality problems of MPIP, with imaging sensors of small and large pixel size, respectively. To leverage the prior information of the optical system, we propose a Point Spread Function (PSF) representation method to produce a PSF map as an additional modality. A PSF-aware Aberration-image Recovery Transformer (PART) is designed as a universal network for the two pipelines, in which the self-attention calculation and feature extraction are guided by the PSF map. We train PART on synthetic image pairs from simulation and put forward the PALHQ dataset to fill the gap of real-world high-quality PAL images for low-level vision. A comprehensive variety of experiments on synthetic and real-world benchmarks demonstrates the impressive imaging results of PCIE and the effectiveness of the PSF representation. We further deliver heuristic experimental findings for minimalist and high-quality panoramic imaging, in terms of the choices of prototype and pipeline, network architecture, training strategies, and dataset construction. Our dataset and code will be available at https://github.com/zju-jiangqi/PCIE-PART.

Athermal panoramic annular lens design with a thermal analysis method

An athermal 360∘×(30∘−100∘) and F/3.5 panoramic annular lens (PAL) system is designed. Through the optical mechanical thermal analysis results based on finite element analysis (FEA), it is expected that the system will have excellent performance under extreme temperature fluctuations. Simulation shows that the system is thermally insensitive in the temperature range from −40∘C to 60°C, consistently providing great imaging capability with the modulation transfer function (MTF) value at 133 lp/mm greater than 0.3. The proposed design and analysis workflow contains an evaluation of thermal optical performance with a higher accuracy, thus having significance in future athermal optical design. We expect the designed PAL system to have a broad application prospect in the field of outdoor applications, including automatic navigation of vehicles and all-weather surveillance systems.

General design algorithm for stray light suppression of a panoramic annular system.

In this work, a universal algorithm for designing a panoramic annular lens (PAL) system free from stray light is proposed. The impact of a given stray light path to the optical system could be estimated without running a full stray light analysis process, which allows designers to eliminate troublesome stray light paths by optimizing lens parameters at an early stage of optical design. A 360° ×(40°-100°) PAL system is designed and implemented to verify the proposed method. Simulation shows that the point source transmittance (PST) decreases by 2 orders of magnitude at a specific field-of-view (FoV) range after optimizing the system. Experimental results show perfect consistency with the simulation predictions, which indicate that two types of stray light are totally eliminated in the demonstrated system. This stray light analysis and suppression method provides a promising approach for the research and development of ultra-wide angle high performance optical systems.

Design of a panoramic annular lens system with an ultra-wide angle via an annular Gaussian radial basis function freeform surface.

The panoramic annular lens (PAL) system can capture plentiful scene information in real time. The locally described freeform surface can provide more degrees of freedom for the optical system design than the globally described one. In this paper, we propose a locally described annular Gaussian radial basis function freeform surface that enables a high-performance yet compact PAL system. The designed PAL system achieves an ultra-wide field of view (FOV) of (30∘∼125∘)×360∘. The F-theta distortion of the system is less than 3%, and the modulation transfer function across the whole FOV is greater than 0.5 at 100lp/mm. The proposed system can be implemented for various applications such as video conferencing or robotic navigation.

Design of a compact triple-channel panoramic stereo imaging system.

We propose a compact form of the triple-channel panoramic annular lens (PAL) with a stereo field and no central blind area based on polarization technology, which solves the problem that the traditional stereo panoramic system always has a large and complex mirror in front to reflect light. Based on the traditional dual-channel structure, we apply polarization technology to the first reflective surface to create a third channel for the stereovision. The field of view (FoV) of the front channel is 360° × (0° - 40°), the FoV of the side channel is 360° × (40° - 105°) and the stereo FoV is 360° × (20° - 50°). The Airy radii of the front channel, the side channel, and the stereo channel are 3.374 µm, 3.372 µm, and 3.360 µm, respectively. The modulation transfer function at 147 lp/mm is greater than 0.13 in the front and stereo channels and greater than 0.42 in the side channel. The F - θ distortion of all FoVs is less than 10%. This system shows a promising way to achieve stereovision without adding complex structures on the original basis.

Panoramic annular image restoration algorithm by prediction based on the lens design characteristics.

A panoramic annular lens optical system is important in circumferential detection. However, a panoramic annular image (PAI) has severe tangential and radial distortion. This study proposes a 3σ guideline-based method, which determines the unwrapping center point of the PAI, and a prediction method based on the lens design characteristics according to the intrinsic distortion of the PAL to correct, respectively, the tangential distortion and the radial distortion. The proposed methods can ensure the restoration ability and simplify the dependence on experimental conditions. The experimental results confirm the effectiveness of the proposed method, thus enabling future panoramic optical image detection.

Wideband High-Gain Omnidirectional Biconical Antenna for Millimeter-Wave Applications

A novel omnidirectional biconical antenna for millimeter-wave (mm-wave) wireless communications is investigated. It is loaded by an annular metal lens that consists of rotationally symmetric annular metal plates (MPs). A nearly uniform <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> -field distribution can be obtained at the radiating aperture across a wide frequency range, giving a wideband high-gain omnidirectional antenna. The operating principle and design flowchart of the lens are given. To validate the idea, a Ka-band vertically polarized prototype was fabricated. Both its measured −10 dB impedance and 3 dB gain bandwidths are 43.9% (25.6–40.0 GHz), with the maximum measured gain given by 9.2 dBi. As compared with the conventional biconical antenna, our antenna can obtain a higher gain by ~4 dB across the entire impedance passband.

Spin-Coating-Based Facile Annular Photodynamic Intraocular Lens Fabrication for Efficient and Safer Posterior Capsular Opacification Prevention.

Posterior capsular opacification (PCO) is the most common complication after cataract surgery, which is primarily caused by the proliferation of the residual lens epithelial cells (LECs) in the lens capsule. Previous studies have demonstrated that a drug-eluting intraocular lens (IOL), aimed to in situ eliminate LECs, are an effective and promising way to prevent PCO. However, because of the potential toxicities of the antiproliferative drugs to the adjacent tissues, the safety of such drug-eluting IOLs is still a highly important issue to be solved. In this investigation, a facile photodynamic coating-modified IOL was developed for effective and safer PCO prevention. An annular poly(lactide-co-glycolic acid) (PLGA) coating loaded with photosensitizer chlorin e6 (Ce6) was prepared by a spin-coating technique. The optical property investigations showed that the Ce6@PLGA coating was particularly suitable for the IOL surface modification. The in vitro cell culture investigation showed that Ce6@PLGA coating-modified IOLs effectively eliminated LECs when treated with light illumination, whereas it appeared to have good cytocompatibility without irradiation. The investigation of the cell elimination mechanism showed that the apoptosis of HLECs may be associated with the cytomembrane disruption induced by ROS, which is generated by the photodynamic coating during light illumination. The in vivo implantation experiments confirmed the desired PCO prevention effect, as well as the safety to and biocompatibility with the surrounding tissues. Thus, the facile Ce6@PLGA coating will provide an effective yet safe alternative of IOL surface modification for PCO prevention.

High-performance compact athermal panoramic annular lens design with separated radial optical power.

A panoramic annular lens can provide abundant spatial information in real time with its compact and scalable structure. To deal with extreme temperature environments and to improve the utilization of an image plane, we propose a high-performance compact athermal panoramic annular lens with separated radial optical power. By introducing multiple free-form surfaces, the system achieves a field of view of (40∘∼100∘)×360∘, an f-number of 2.2, and a total length of 40 mm. The modulation transfer function of the system's full fields of view is greater than 0.5 at 200 lp/mm, and the distortion is less than 2.5%. It can work stably in the range of -30∘C to 70°C. The proposed system is compact, athermal, and high-performing and has broad application prospects in the fields of visual positioning and biomedicine.

Compact and lightweight panoramic annular lens for computer vision tasks.

We propose a focal power distribution theory for the design of a compact panoramic annular lens (PAL) system based on Petzval sum correction. The system has a large field of view (FoV) of 360° ×(25°-100°). Its total length is 29.2 mm and weight is only 20 g. The proposed compact PAL system achieves large FoV and loose tolerances while maintaining small volume and low cost. It solves the shortcomings of traditional PAL systems that cannot be mounted on miniaturized portable devices due to their large volume and weight. We equip the compact PAL system with a novel and customized image enhancement model: PAL-Restormer to achieve better imaging quality. The produced images are further evaluated in various panoramic environment perception tasks. Extensive experiments show the promising potential of our proposed compact PAL system for the applications in wearable devices and mobile robots.

Design of stereo imaging system with a panoramic annular lens and a convex mirror.

Panoramic stereo imaging system can not only provide panoramic images to obtain more information, but also obtain the depth information of the target object, and it has broad application prospects in robot navigation, road planning, and obstacle avoidance. A new panoramic stereo imaging system combined with a panoramic annular lens (PAL) and a convex mirror is proposed. It provides a large panoramic vision up to 360°× (30°∼150°) and, to the best of our knowledge, the entire FOV is the largest in the existing literature. Meanwhile, the stereo field of view is 35°.

Size reduction of a conical horn antenna loaded by multi‐layer metamaterial lens

In this paper, a conical horn antenna in the presence of a metamaterial lens in the X-band is introduced and fabricated. The annular metamaterial lens is located at the aperture of a shortened horn antenna, whose length is half the length of the corresponding optimum horn. The phase velocity in the metamaterial lens is more than the phase velocity along the axis of the antenna for the same propagation distance, so the phase distribution at the aperture of the antenna is uniform and the gain of the shortened horn antenna increases. Metamaterial cells are designed in the form of a printed circuit board that have easy to build and suitable cost. The design process is based on how the waves incident on the proposed metamaterial cell, and finally, by using the particle swarm optimisation (PSO) algorithm proper radiation characteristics in the desired frequency range can be achieved. The radiation characteristics of an antenna with a metamaterial lens are similar to that of an antenna with optimum length in the desired frequency band. The difference is that the weight and volume of these antennas are reduced, so they have better performance in satellite and radar systems.

Wideband Omnidirectional Circularly Polarized Antenna for Millimeter-Wave Applications Using Conformal Artificial Anisotropic Polarizer

A wideband omnidirectional circularly polarized (CP) antenna using a conformal artificial anisotropic polarizer is proposed for millimeter-wave applications. The antenna consists of three parts: an omnidirectional linearly polarized (LP) radiator, an annular hyperbolic lens, and a conformal anisotropic polarizer. The annular hyperbolic lens regulates the spherical wavefront from the LP radiator into a cylindrical shape prior to propagating into the conformal artificial anisotropic polarizer. Each curved slab of the polarizer is conformally tilted 45° to the incident electric field. Therefore, the conformal polarizer is the three-dimensionalization of the 2-D planar artificial anisotropic polarizer. The polarizer designing methodology is the first of its kind to generate wideband CP wave omnidirectionally. The hyperbolic lens and the conformal polarizer are fabricated together using stereolithography (SLA) 3-D printing technology. The measurement results show that the antenna has a wide operating bandwidth of 45% (from 24 to 38 GHz), which completely covers potential 5G 28 GHz spectra. The proposed design has a low fabrication complexity and brings possibilities for high-speed wireless communications using circular polarization.